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Friday, April 27, 2012
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Bellave Shivaram
[Host: Brad Cox]
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4:00 PM, Room 204
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University of Virginia |
| Physics Building |
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“101 Years of Superconductivity - My Contributions Therein” |
ABSTRACT:
| Starting from a brief history of its initial discovery I will trace the development/study of various classes of superconducting materials.
I will cover the phenomenology in these different classes with references to microscopic theory where appropriate, and also present a concurrent description of my own experimental contributions. |
Special Colloquium: Hoxton Lecture
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Thursday, April 12, 2012
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Edward Moses
[Host: Brad Cox]
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7:00 PM, Room 402
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National Ignition Facility |
| Chemistry Building |
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“The National Ignition Facility: Pathway to Energy Security and Physics of the Cosmos” |
ABSTRACT:
| The National Ignition Facility (NIF), at Lawrence Livermore National Laboratory in
Livermore, California, is the world’s most energetic laser system. NIF is capable of
producing over 1.8 MJ and 500 TW of ultraviolet light, 100 times more than any other
operating laser. Completed in March 2009, it is maturing rapidly and transitioning into
the world’s premier high-energy-density science experimental facility, while supporting
its strategic security, fundamental science, and energy security missions.
By concentrating intense laser energy into target only millimeters in length, NIF can, for
the first time, produce conditions emulating those found in planetary interiors and stellar
environments and creating fusion energy to power our future. The extreme conditions of
energy density, pressure, and temperature will enable scientists to pursue fundamental
science experiments designed to address a range of scientific questions, from observing
new states of matter to exploring the origin of ultrahigh-energy cosmic rays. Early
experiments have been successfully completed in support of materials equations of state,
materials strength, and radiation transport in extreme temperature and pressure
conditions.
The National Ignition Campaign, an international effort pursued on the NIF, aims to
demonstrate fusion burn and generate more energy output than the laser energy delivered
to the target. Achieving this ignition goal will validate the viability of inertial fusion
energy (IFE) as a clean source of energy. A laser-based IFE power plant will require
advances in high-repetition-rate lasers, large-scale target fabrication, target injection and
tracking, and other supporting technologies. These capabilities could lead to an
operational prototype IFE power plant in 10 to 15 years. LLNL, in partnership with
academia, national laboratories, and industry, is developing a Laser Inertial Fusion
Energy (LIFE) baseline design concept and examining technology choices for developing
a LIFE prototype power plant.
This talk will describe the unprecedented experimental capabilities of the NIF, its role in
strategic security and fundamental science, and the pathway to achieving fusion ignition
to create a clean and secure energy future. |
ABSTRACT:
| Understanding the structure of matter in terms of its underlying constituents has a long tradition in science. A key question is how we can understand the properties of the proton, such as its mass, charge, and spin (intrinsic angular momentum) in terms of its underlying constituents: nearly massless quarks (building blocks) and massless gluons (force carriers). The strong force that confines quarks inside the proton leads to the creation of abundant gluons and quark-antiquark pairs (QCD sea). These ‘silent partners’ make the dominant contribution to the mass of the proton. Various polarized deep-inelastic scattering measurements have shown that the spins of all quarks and antiquarks combined account for only 25% of the proton spin. New experimental techniques are required to deepen our understanding on the role of gluons and the QCD sea to the proton spin. High energy polarized proton-proton (p + p) collisions at RHIC at Brookhaven National Laboratory provide a new and unique way to probe the proton spin structure using very well established processes in high-energy physics, both experimentally and theoretically. A major new tool has been established for the first time using parity-violating W boson production in polarized p + p collisions at √s = 500 GeV demonstrating directly the different polarization patterns of different quark flavors, paving the path to study the polarization of the QCD sea. Various results in polarized p + p collisions at √s = 200 GeV constrain the degree to which gluons are polarized suggesting that the contribution of the gluons to the spin of the proton is rather small, in striking contrast to their role in making up the mass of the proton. |
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Friday, March 23, 2012
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Sir David King
[Host: John T. Yates, Jr., Ian Harrison, & Brad Cox]
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4:00 PM, Room 203
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Smith School at Oxford |
| Physics Building |
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“A Scientific Analysis of 21st Century Environmental and Economic Challenges” |
ABSTRACT:
| Unprecedented improvements in human wellbeing over the nineteenth and twentieth centuries have been driven largely by developments flowing from advances in engineering, medicine, agriculture and technology, and by political and economic developments coupled to consumerism. But a necessary consequence of these successes has been an equally unprecedented growth in the global population. The twenty first century will be dominated by the challenges posed by a mid-century population of around 9 billion people, all seeking a high standard of living. Ecosystem services, an essential element of our continued wellbeing as a species, are already under threat as our need for food production, fresh water, energy sources, minerals etc. grows exponentially to meet unfettered demand. Climate change, driven by fossil fuel usage and by deforestation, provides the biggest challenge of all, since it requires a collective response of the global population, to mitigate the effect and to manage the growing impacts upon our societies.
Well designed technological solutions are desirable and can be compatible with the continued growth of human wellbeing. The socio-political challenges in directing such a collective response are beyond anything previously managed. This may well lead to a mid-century slide into conflict caused by environmental and resource-driven challenges on a scale not previously experienced. The thesis presented here is that meeting these challenges will require a global cultural and technological transformation on much the same scale as the European Renaissance or the Industrial Revolution itself, and a clear understanding by all societies of the need to adapt and strengthen global governance procedures. Decision making at all levels will require significantly enhanced knowledge and understanding. |
Special Colloquium: Institute of Nuclear and Particle Physics Annual Lecture
ABSTRACT:
| The "Minimal" Standard Model of particle physics is almost complete. Interesting hints of a standard Higgs Boson are starting to appear at CERN and one can ask, Is it all that remains to be discovered? Dark matter observations suggest that an invisible universe of massive particles may exist all around us, but coupled to normal matter primarily by gravity. Can we detect dark particles and study their properties at accelerators? In this talk, I will discuss the implications of a Higgs Boson discovery and speculate on its possible connection to "dark" matter physics. In particular, properties of the "dark" photon, a hypothetical "dark" force carrier,
along with ongoing and proposed experimental efforts to discover, it will be described. |
ABSTRACT:
| There are today over 440 commercial nuclear power reactors operating in 30 countries. They provide about 14% of the world's electricity in the form of economic, environmentally sound and reliable base-load power. In addition, 63 new nuclear reactors are currently under construction in 14 countries. But much has changed in the design of nuclear reactors since the first commercial nuclear power stations started operating in the 1950s. Modern nuclear reactors, those that will be built in the short term, achieve improvements over existing designs through small to moderate modifications, with a strong emphasis on maintaining design provenness and building upon the lessons learnt from 40 years of successful operation, to minimize technological and investment risks. At the same time, nuclear designers are already working on a new generation of nuclear reactor concepts incorporating radical conceptual changes in design approaches or system configuration in comparison with existing practice. Substantial research and development efforts, feasibility tests, as well as a prototype or demonstration plant are probably required prior to the commercial deployment of these innovative designs. This talk will provide an overview of the most recent developments in nuclear reactor design, including those using alternative fuel cycles, such as Thorium. |
Special Colloquium
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Thursday, February 23, 2012
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Xiang Cheng
[Host: Seunghun Lee]
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3:30 PM, Room 204
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Cornell University |
| Physics Building |
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“Imaging the microscopic structure of shear thinning and thickening colloidal suspensions” |
ABSTRACT:
| While a simple Newtonian fluid such as water flows with a constant viscosity, many structured fluids ranging from polymer melts to surfactant solutions exhibit fascinating non-Newtonian flow behaviors including shear thinning and shear thickening. One typical example is a colloidal suspension, where its viscosity can vary by orders of magnitude depending on how quickly it is sheared. Although these non-Newtonian behaviors are believed to arise from the arrangement of suspended particles and their mutual interactions, microscopic particle dynamics in such suspensions are difficult to measure directly. Here, by combining fast confocal microscopy with simultaneous force measurements, we systematically investigate a suspension's structure as it transitions through regimes of different flow signatures. Our measurements of the microscopic single-particle dynamics unambiguously show that shear thinning results from the decreased relative contribution of entropic forces and that shear thickening arises from particle clustering induced by inter-particle hydrodynamic lubrication forces. Furthermore, we explore out-of-equilibrium structures of sheared colloidal suspensions and report a novel string phase, where particles link into log-rolling strings normal to the plane of shear. Our techniques illustrate an approach that complements current methods for determining the microscopic origins of non-Newtonian flow behavior in complex fluids. |
Special Colloquium
ABSTRACT:
| In geometrically frustrated magnets (GFMs), the incompatibility between the interactions of the magnetic degrees of freedom in a lattice and the underling crystal geometry leads to the frustration. The massive level of degeneracy introduced by this frustration can persist to low temperatures to enhance the spin fluctuations and suppress the magnetic ordering, therefore resulting exotic spin ground states with abnormal thermo-dynamics. In this talk, two GFMs will be introduced: (i) Spin ice with pyrochlore structure, in which the ground state is a short range ordering of the “two spin in two spin out” configurations on tetrahedrons following the “ice rule”; (ii) Quantum spin liquid (QSL), in which the strong quantum fluctuations of the spins with small number (S = 1/2 and 1) destroy the magnetic ordering and lead to a spin-liquid like ground state. Following the introduction, we present our recently studies on new pyrochlore materials Pr2Sn2O7 and Dy2Ge2O7, and new QSL materials Ba3CuSb2O9 and Ba3NiSb2O9 with a triangular lattice of S = 1/2 and S = 1, respectively. |
Special Colloquium
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Thursday, February 16, 2012
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Cheng Cen
[Host: Seunghun Lee]
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3:30 PM, Room 204
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IBM |
| Physics Building |
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“Oxide Nanoelectronics on Demand” |
ABSTRACT:
| Complex oxides and their heterostructures have exhibited a great collection of novel functionalities and are considered one of the most promising candidate for next generation technological materials. At the interface formed between LaAlO3 and SrTiO3, by scanning a biased conducting atomic force microscope (AFM) tip along a programmed trajectory at room temperature, we can reversibly control in nanoscale the metal-insulator transition. With this technique, a variety of rewritable nanoscale devices and structures have been studied. These nanostructures, which are mainly assembled from basic elements including conductive wires and dots with characteristic dimensions just a few nanometers, show great performance as field effect transistors, nanodiodes and photodetectors. At low temperatures, a variety of electronic, spintronic and superconducting properties are observed, with enormous potential for exploitation in quantum devices. |
Special Colloquium
ABSTRACT:
| In strongly-correlated materials, such as high-temperature superconductors and heavy fermion compounds, electrons form many-body states with properties different from those of non-interacting electrons. A simpler and better understood example of electron correlations is the Kondo effect, which describes how spins of conduction electrons screen the spin of a localized electron that has degenerate spin states (spin-up and spin-down in the case of a localized spin-1/2 electron). This screening generates spin correlations. Electrical transport measurements of a single quantum dot can probe Kondo physics; however, to directly access the spin correlations one needs spin-resolved measurements. We address this challenge by using the orbital states of a double quantum dot as pseudo-spin states: an electron on the left/right dot is associated with pseudo-spin up/down. When the energies of these pseudo-spin states are degenerate, Kondo screening occurs. We establish a correspondence between spin Kondo in a single dot and pseudo-spin Kondo in double dots. We use this to show that our pseudo-spin resolved spectroscopy measurements of the Kondo state in a double dot correspond to predictions for spin-resolved spectroscopy of spin Kondo. Finally, we explore the interplay between orbital and spin degeneracy in this double dot system. |
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Friday, February 10, 2012
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Robert W. Michaels
[Host: Xiaochao Zheng]
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4:00 PM, Room 204
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Thomas Jefferson National Accelerator Facility |
| Physics Building |
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“The Lead Radius Experiment PREX” |
ABSTRACT:
| The Lead Radius Experiment PREX ran in the Spring of 2010 in Hall A at the Thomas Jefferson
National Accelerator Facility (JLab). The experiment measures the parity-violating asymmetry in the elastic scattering of longitudinally polarized electrons from a 208Pb nucleus at an energy of 1.06 GeV and a scattering angle of 5◦. The Z boson that mediates the weak neutral interaction couples mainly to neutrons and provides a clean, model-independent measurement of the RMS radius Rn of the neutron distribution in the nucleus. This measurement is a fundamental test of nuclear structure theory, and our result establishes the existence of the neutron skin, i.e. that Rn > Rp. A precise measurement of Rn pins down the density-dependence of the symmetry energy of neutronrich
nuclear matter, which has impacts on neutron star structure, heavy ion collisions, and atomic
parity violation experiments. The experiment involves all aspects of the JLab accelerator, from
the polarized source to the detector, and capitalizes on JLab’s unique strengths for carrying out high-precision parity experiments. In addition to the 2010 data, several technical challenges will be described, as well as prospects for future measurements at JLab from 208Pb and other nuclei such as 48Ca. |
Special Colloquium
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Thursday, February 9, 2012
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Kenjiro Gomes
[Host: Seunghun Lee]
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3:30 PM, Room 204
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Stanford University |
| Physics Building |
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“Tailoring Dirac Fermions in Molecular Graphene” |
ABSTRACT:
| The dynamics of electrons in solids is tied to the band structure created by a periodic atomic potential. The design of artificial lattices, assembled through atomic manipulation, opens the door to engineer electronic band structure and to create novel quantum states. We present scanning tunneling spectroscopic measurements of a nanoassembled honeycomb lattice displaying a Dirac fermion band structure. The artificial lattice is created by atomic manipulation of single CO molecules with the scanning tunneling microscope on the surface of Cu(111). The periodic potential generated by the assembled CO molecules reshapes the band structure of the two-dimensional electron gas, present as a surface state of Cu(111), into a "molecular graphene" system. We characterize the band structure through Fourier transform analysis of impurity scattering maps. We tailor this new tunable class of graphene to reveal signature topological properties: an emergent mass and energy gap created by breaking the pseudospin symmetry with a Kekule bond distortion; gauge fields generated by applying atomically engineered strains; and the condensation of electrons into quantum Hall-like states and topologically confined phases. |
ABSTRACT:
The polaron is a mathematical model for a “dressed”
particle consisting of an electron together with its entourage of
local excitations of a quantized phonon field. We will give a brief
historical review of the polaron, including the analysis of its ground
state by a Brownian motion functional integral and by a related
variational expression.
For the case of two or more electrons,
the interaction of the electrons with the phonon field gives rise to
an effective attraction between electrons that causes the particles to
bind together. For N electrons, N → ∞, the
systems are unstable in the sense that the binding energy grows faster
than linearly in N. We will discuss recent work with Frank,
Lieb, and Seiringer which shows that sufficiently strong Coulomb
repulsion between electrons can compensate for this binding and
provide stability for polaron systems for large N. |
Special Colloquium
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Thursday, January 26, 2012
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Utpal Chatterjee
[Host: Seunghun Lee]
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3:30 PM, Room 204
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Argonne National Laboratory |
| Physics Building |
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“Characterizing phase diagram of High Temperature Superconductors via Angle Resolved Photoemission Spectroscopy” |
ABSTRACT:
| High Temperature Superconductors (HTSCs) were discovered more than 25 years ago.
However, a microscopic theory of them is yet to be realized. In order to identify the
mechanism behind superconductivity in these systems, we must understand the normal
state from which superconductivity emerges. From our detailed Angle Resolved
Photoemission Spectroscopy (ARPES) measurements on Bi2Sr2CaCu2O8+δ (BISCO 2212) HTSCs we have found that unlike conventional superconductors, where there is a single temperature scale Tc separating the normal from the superconducting state, HTSCs
are associated with two additional temperature scales. One is the so-called pseudogap
scale T*, below which electronic states are partially gapped, while the second one is the
coherence scale Tcoh, characterizing the onset of a significant enhancement in electronic
lifetime. We have observed that both T* and Tcoh change strongly with carrier
concentration and they cross each other near optimal doping, i.e. the carrier concentration
at which an HTSC attains its maximum Tc. Furthermore, there is an unusual phase in the
normal state where the electronic excitations are gapped as well as coherent. Quite
remarkably, this is the phase from which the superconductivity with maximum Tc
emerges. Our experimental finding that T* and Tcoh intersect is not compatible with the
theories invoking “single quantum critical” point near optimal doping, rather it is more
naturally consistent with the theories of superconductivity for doped Mott insulators. |
ABSTRACT:
| Supersymmetry is a theory build under the hypothesis that there is a relation between bosons and fermions. The particle physics community finds it very compelling because it provides a solution to the mass hierarchy problem, allows a percent level unification of gauge couplings, and predicts a particle candidate for dark matter. The Large Hadron Collider (LHC) at CERN is the best instrument with count with at the moment to search for supersymmetric particles. It has delivered proton-proton collisions at a center of mass energy of 7 TeV since 2010. The CMS and ATLAS experiments at the LHC are expected to collect 4-5 fb-1 of data before the end of 2011 and explore a very significant fraction of the phase space associated with the most simple supersymmetric models. This talk will go over the experimental strategy for SUSY searches at the LHC, explain the techniques to evaluate the main backgrounds to potential SUSY signals, and review the most recent results. |
Special Colloquium
ABSTRACT:
| I will give an overview of applications of atomic calculations for atomic physics tests of fundamental physics, including the study of parity violation, search for EDM, and search for variation of fundamental constants. The goals of high-precision atomic parity violation (APV) studies are to search for new physics beyond the standard model of the electroweak interaction by accurate determination of the weak charge and to probe parity violation in the nucleus. I will discuss the current status and future prospects of atomic parity violation studies and the implications for searches for physics beyond the standard model. The recent advances in theoretical methodology that allowed to reduce theoretical uncertainty in the analysis of the cesium experiment are briefly outlined. I will also discuss recent accurate calculation of the nuclear spin-dependent parity-violating amplitude. New result still leads to the discrepancy between constraints on weak nucleon-nucleon coupling obtained from the cesium anapole moment and those obtained from other nuclear PV measurements. |
ABSTRACT:
| A dimensionless measure of fluidity is the ratio of shear viscosity to entropy density. In this talk we will argue that fluidity is a sensitive probe of the strength of correlations in a fluid. We will also discuss evidence that the two most perfect fluids ever observed are also the coldest and the hottest fluid ever created in the laboratory. The two fluids are cold atomic gases (~10^(-6) K) that can be probed in optical traps, and the quark gluon plasma (~10^{12} K) created in heavy ion collisions at RHIC (Relativistic Heavy Ion Collider at Brookhaven National Laboratory). Remarkably, both fluids come close to a bound on the shear viscosity that was first proposed based on calculations in string theory, involving non-equilibrium evolution of back holes in 5 (and more) dimensions. |
Special Colloquium
Special Colloquium
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Friday, October 28, 2011
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Di Xiao
[Host: Joe Poon]
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4:00 PM, Room 204
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Oak Ridge National Lab |
| Physics Building |
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“Topological Insulators: From Fundamentals to Applications” |
ABSTRACT:
| Topological insulators are materials that have a bulk band gap like an ordinary insulator but support protected conducting states on their edge or surface. These edge/surface states are predicted to have special properties that could be useful for applications ranging from spintronics to quantum computing. In this talk, I will explain the nontrivial band topology of these materials using the Berry phase concept, review current progress on material prediction and realization, and discuss some of the applications in surface catalysis and electronics. |
Special Colloquium
ABSTRACT:
| All fields of scientific research have experienced an explosion of data. It is a formidable computational challenge to analyze this data to extract unexpected patterns. Meeting this challenge will require new, advanced methods of analysis. Dynamic Quantum Clustering is such a tool. The algorithm, invented by David Horn (Tel Aviv University) and myself, provides a highly visual and interactive tool that allows one to explore complicated data that has unknown structure. My talk will provide a brief introduction to the distinction between supervised and unsupervised methods in data mining (clustering in particular). Then, I will, very briefly, discuss the theory of DQC. The bulk of my talk will be devoted to showing results on a data set coming from the Stanford Synchrotron Radiation Laboratory and some results from data on earthquakes in the Middle East. These examples show the power of DQC applied to data sets on which the currently most favored unsupervised data mining techniques fail to obtain any interesting results. The message will be that large, complex, data sets typically exhibit extended structures that are significant and that cannot be seen by other methods. |
Special Colloquium
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Friday, October 14, 2011
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Francis Robicheaux
[Host: Bob Jones]
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4:00 PM, Room 204
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Auburn University |
| Physics Building |
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“Antihydrogen Trapped” |
ABSTRACT:
| Atoms made of a particle and an antiparticle are unstable, usually surviving less than a microsecond. Antihydrogen, the bound state of an antiproton and a positron, is made entirely of antiparticles and is believed to be stable. It is this longevity that holds the promise of precision studies of matter-antimatter symmetry. Low energy (Kelvin scale) antihydrogen has been produced at CERN since 2002. I will describe the experiment which has recently succeeded in trapping antihydrogen in a cryogenic Penning trap for times up to approximately 15 minutes. |
Colloquium: Kickoff Event for The Optical Society of America at UVA
ABSTRACT:
| Nonlinear optics, which governs the interaction of light with various media, offers a whole raft of useful applications in photonics, including multiphoton microscopy and multiphoton lithography. It also provides the physicist with a remarkable range of opportunities for generating light with interesting, novel, and potentially useful properties. As a particular example, entangled-photon beams generated via spontaneous optical parametric down-conversion exhibit unique quantum-correlation features and coherence properties that are of interest in a number of contexts, including imaging. Photons are emitted in pairs in an entangled quantum state, forming twin beams. Such light has found use, for example, in quantum optical coherence tomography, a quantum imaging technique that permits an object to be examined in section. Quantum entanglement endows this approach with a remarkable property: it is insensitive to the even-order dispersion inherent in the object, thereby increasing the resolution and section depth that can be attained. We discuss the advantages and disadvantages of a number of techniques in multiphoton and entangled-photon imaging and lithography. |
ABSTRACT:
| The Los Alamos and Lawrence Livermore National Laboratories are the two largest employers of physicists in the country. Their primary mission is nuclear weapons science. Based on over two decades studying the culture of nuclear weapons scientists as an anthropologist, the speaker discusses the values of nuclear weapons physicists, the reasons young physicists have for choosing a career in nuclear weapons design, the ethical challenges they confront, and the degree of job satisfaction they report. |
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Friday, September 16, 2011
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John Delos
[Host: Tom Gallagher]
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4:00 PM, Room 204
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College of William and Mary |
| Physics Building |
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“Electronic Detection and Diagnosis of Health and Illness of Premature Infants” |
ABSTRACT:
| The pacemaking system of the heart is complex; a healthy heart constantly integrates and responds to extracardiac signals, resulting in highly complex heart rate patterns with a great deal of variability. In the laboratory and in some pathological or age related states, however, dynamics can show reduced complexity that is more readily described and modeled. Reduced heart rate complexity has both clinical and dynamical significance - it may provide warning of impending illness or clues about the dynamics of the heart's pacemaking system. Here we describe simple and interesting heart rate dynamics that we have observed in premature human infants - reversible transitions to large- amplitude periodic oscillations - and we show that they give early warning of bacterial infections in premature infants, and we show that the appearance and disappearance of these periodic oscillations can be described by a simple mathematical model, a Hopf bifurcation. |
ABSTRACT:
| Atoms at ultralow temperatures are fascinating quantum objects, which can tunnel through barriers, repel or attract each other, and interfere like electromagnetic waves. This wavy behavior of ultracold atoms evidently illustrates the particle-wave duality as discussed in modern physics.
By loading repulsively interacting atoms into a regular array of tiny optical cells (called optical lattices), we show that the wavy nature of the atoms can be completely destroyed. At the same time, the gaseous sample develops an interesting multi-layer structure with quantize density plateaus, resembling a multi-tier wedding cake.
Our observation of the cake structure in ultracold gases of atoms [1] raises new prospects to investigate the dynamics and transport across a phase boundary [2] and to identify universal critical behavior in the transition regime [3]. Surprising findings along these directions will be reported. |
ABSTRACT:
| The physical length of one copy of the human genome is a little over 1 meter. It is packaged into a nucleus, which is on the order of micrometers in diameter. This is achieved by wrapping the DNA around histones. In the last decade, many breakthroughs have lead to the understanding that these histones control subsets of genes that are turned on or off depending on chemical modifications on their tails. They accomplish this by controlling the accessibility of proteins—responsible for turning genes on—to DNA. This accessibility can be characterized by two
states: open and closed. Remarkably, over 60 different locations on these tails are subject to at least one of eight types of chemical modifications.
Recently, it has been shown that many of these modifications work together to robustly turn genes on or off; however, we are at the beginning of uncovering this complex control network. To shed light on this network, we apply computational methods, which identify statistically significant combinations, to genome wide maps of histone modifications. We indeed find that crosstalk among these modifications is extensive and predict novel combinations, which strongly synergize in our models, for further biochemical study.
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National Physics Day Show
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Wednesday, April 27, 2011
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A Family-Oriented Event
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7:00 PM, Room 203
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| Physics Building |
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“Physics professors Bob Jones, Olivier Pfister, Cass Sackett, and Steve Thornton will delight the crowd with strange and mystifying events.” |
ABSTRACT:
| See rockets shooting around the auditorium, balls suspended in air, curve balls flying overhead, Van de Graaff generators, skaters spinning around. You will see you a bunch of fascinating things you should never do at home. We might even put someone on a bed of nails and crush a cement block on top of them. As usual, there will be plenty of surprises in store. These demonstrations will intrigue and excite both young and old and from novice to expert. Bring your family and friends, but come on time. For more information about this free public event call 924-3781.
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Friday, April 22, 2011
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Sylvester J. Gates
[Host: Diana Vaman]
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4:00 PM, Room 204
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University of Maryland |
| Physics Building |
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“The Quincunx Point” |
ABSTRACT:
| Sometimes theoretical physics problems resist resolution for decades. Endeavoring to solve such problems can lead to a new and unexpected viewpoint. Prof. Gates will describe such a problem and describe how trying to solve it has possibly led to a quincunx point at the five-fold overlap of art, mathematics, music, science, and perhaps... |
ABSTRACT:
| Historically, two paradigms competed to explain superconductivity (i) Bose Einstein Condensation of weakly interacting Charge 2e pairs (Schafroth),
and (ii) Pairing instability of the Fermi liquid (BCS). BCS theory was the unquestionable winner until the late 80's.
BCS approximations however, have suffered major setbacks in the advent of high temperature, short coherence length superconductors, such as cuprates, pnictides, and granular superconducting films.
A third paradigm has offered itself: Hard Core lattice Bosons (HCB), which are experimentally realized in cold atoms on optical lattices.
HCB behave less like weakly interacting bosons or fermions, but (strangely) more like quantum spins. Their static correlations are very well understood by theories of quantum antiferromagnets.
Recent calculations of the conductivity of Hard Core Bosons suggests a new route to understanding linear in temperature resistivity and other strange metallic properties above the transition temperature.
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Hoxton Lecture
ABSTRACT:
| Professor Richter is the co-winner of the 1976 Nobel Prize in physics for the discovery of the J/Ψ particle which was the first observation of a particle containing a fourth quark named the charm quark and was a central part of the so-called November revolution of particle physics. He has accumulated many other honors in his career including a long tenure as the director of Stanford Linear Acceleratory Laboratory from 1984 to 1999. He has also been the recipient of the E.O. Lawrence Medal, has served as president of the American Physical Society, and is a member of the National Academy of Sciences. He presently serves on the board of directors of Scientists and Engineers for America, an organization focused on promoting sound science in American government and is a Senior Fellow by Courtesy of the Center for Environmental Science and Policy at Stanford Institute for International Studies. In the past several years Professor Richter has turned his attention to the central problem of the 21st century, the effect of human activity on the global climate. He has written a book with the same title as his lecture. |
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Friday, April 1, 2011
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Grad Poster Competition
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4:00 PM, Room 204
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| Physics Building |
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Friday, February 18, 2011
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Peter Lu
[Host: Peter Arnold]
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4:00 PM, Room 204
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Harvard University |
| Physics Building |
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“Modern math in medieval islamic architecture” |
ABSTRACT:
| The conventional view holds that girih (geometric star-and-polygon) patterns in medieval Islamic architecture were conceived by their designers as a network of zigzagging lines, and drafted directly with a straightedge and a compass. I will describe recent findings that, by 1200 C.E., a conceptual breakthrough occurred in which girih patterns were reconceived as tessellations of a special set of equilateral polygons (girih tiles) decorated with lines. These girih tiles enabled the creation of increasingly complex periodic girih patterns, and by the 15th century, the tessellation approach was combined with self-similar transformations to construct nearly-perfect quasicrystalline patterns. Quasicrystal patterns have remarkable properties: they do not repeat periodically, and have special symmetry---and were not understood in the West until the 1970s. I will discuss some of the properties of Islamic quasicrystalline tilings, and their relation to the Penrose tiling, perhaps the best known quasicrystal pattern.
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ABSTRACT:
| The first galaxies were small condensations of baryonic matter that fell into the gravitational potentials of dark-matter halos, and larger galaxies are still being assembled from smaller ones by heirarchical merging. Black holes quickly formed and grew in their centers, and energy feedback from these supermassive black holes
(SMBHs) dominated the subsequent growth and stellar composition of large galaxies, making them "red, dead, and elliptical" today. To constrain the role of SMBHs in galaxy evolution we recently measured accurate nuclear masses of six Seyfert galaxies using the Keplerian rotation curves of circumnuclear water masers observed with 0.0003 arcsec resolution. The nuclear mass densities are so high that they are consistent only with supermassive black holes, not dense star clusters. Because nearly all galaxies contain SMBHs, recently merged galaxies should contain inspiraling binary SMBHs that may merge and emit very energetic and anisotropic bursts of gravitational radiation.
We recently began the first systematic search for inspiraling, binary, or recoiling SMBHs in hundreds of nearby massive galaxies.
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Special Colloquium
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Tuesday, February 8, 2011
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Chris Neu
[Host: Joe Poon]
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3:30 PM, Room 204
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University of Virginia |
| Physics Building |
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“Top Quarks at the Large Hadron Collider: In Pursuit of Truth and its Consequences” |
ABSTRACT:
| The top quark is a unique member of the collection of known fundamental particles. Its mass is exceedingly large -- nearly that of a single atom of gold -- which is remarkable given that the top quark is considered to be a point particle with no substructure.
Further, the top quark decays rapidly, long before having the chance to form a bound state with other quarks. Hence, the study of top-quark decays affords a direct glimpse at the properties of the parent quark itself, allowing measurements of its mass, spin, charge and other properties. Finally, several signatures of new phenomena accessible at particle colliders either suffer from top-quark production as a significant background or contain top quarks themselves. With the advent of the operational era of the Large Hadron Collider (LHC), the Compact Muon Solenoid (CMS) experiment has the opportunity to perform precision measurements of top-quark production and decay for the first time away from Fermilab's Tevatron collider, whose experiments produced the discovery of the top quark in 1994. In this talk I will present some of the first results of the CMS top-quark physics program, results in which members of the University of Virginia CMS group made significant contributions.
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Friday, February 4, 2011
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Israel Klich
[Host: Joe Poon]
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4:00 PM, Room 204
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University of Virginia |
| Physics Building |
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“Entanglement and Entropy in many body systems” |
ABSTRACT:
| As physical systems are cooled down, their properties may no longer be described in classical terms, and we enter a quantum regime. Perhaps the most fascinating quantum property is entanglement. Recently, with understanding of entanglement between a few particles, many-body entanglement has received great interest in such varied fields as condensed matter, cosmology and quantum information. Indeed, the scaling of entanglement in large systems is a sensitive measure of the nature of interactions and phases. In contrast with typical thermodynamical behavior, the entanglement entropy of a sub region in a physical system often grows as it's boundary area, and not as its volume. In this talk, I will describe such “area laws”, their appearance and relation to quantum phase transitions. I will also discuss a yet more detailed analysis of such entanglement, known as entanglement spectrum. Finally, I will exhibit a universal relation between entanglement and statistics of current flowing through a quantum point contact, which provides a way to experimentally measure entanglement entropy. |
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Friday, January 28, 2011
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Stephen Martin
[Host: Brad Cox]
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4:00 PM, Room 204
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Northern Illinois University |
| Physics Building |
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“Supersymmetry” |
ABSTRACT:
| Supersymmetry is a proposed symmetry of particle physics that relates fermions and bosons to each other. It makes the exciting prediction that for every known elementary particle there is a heavier "superpartner" particle waiting to be discovered. One of these superpartners may be the dark matter required by astrophysical and cosmological observations. I will explain the motivations behind supersymmetry, the predicted properties of the superpartner particles, and review indirect evidence suggesting that at least some of them are likely to be discovered at the Large Hadron Collider within the next few years. Several of the most likely possibilities for the discovery signature for superpartners will be discussed. |
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Friday, January 21, 2011
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Stan Williams
[Host: Stu Wolf]
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4:00 PM, Room 204
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HP |
| Physics Building |
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“Memristance and Negative Differential Resistance in Transition Metal Oxides” |
ABSTRACT:
| Memristive devices are nonlinear dynamical systems that exhibit continuous, reversible and
nonvolatile resistance changes that depend on the polarity, magnitude and duration of an applied
electric field. The memristive properties of metal/metal oxide/metal (MOM) materials
systems were discovered in the 1960s and studied without reaching a consensus on the physical
mechanism, while the theoretical foundation of memristance was derived by Chua in 1971
without realizing there were physical examples of this circuit property. Recent studies on the
mechanism revealed that memristive switching is caused by electric field-driven motion of
charged dopants that define the interface position between conducting and semiconducting regions
of the film. There have also been multiple reports of current-controlled negative differential
resistance (CC-NDR) in electroformed MOM devices since the early 1960s (e.g. oxides
of V, Nb, Ta, Ti and Fe), and there have been a variety of proposals for the physical mechanism.
Current work presents persuasive evidence that CC-NDR in these materials is due to a
Joule-heating induced metal-insulator transition (MIT). We have found that both memristance
and CC-NDR coexist in many transition metal oxides, and the fact that both effects have been
called "switching" has caused a great deal of confusion in the literature and prevented
comprehensive understanding of these systems. I will explain the origin of both effects in
titanium oxides and show some potential applications of combining the two effects in a
single nanoscale device. |
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Friday, December 3, 2010
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John Brenkus
[Host: Lou Bloomfield]
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4:00 PM, Room 204
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ESPN |
| Physics Building |
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“Sport Science and the Perfection Point” |
ABSTRACT:
| UVA alum John Brenkus will talk about the science of sport, drawing upon his vast experience as the creator, executive producer, and host of the Emmy Award-winning show “Sport Science” on ESPN. He will also discuss his recent book "The Perfection Point," which debuted at #1 on BarnesAndNoble.com when it was released on September 1.
On “Sport Science,” Brenkus has the top athletes on the planet into his state-of-the-art laboratory to uncover sports’ biggest myths and mysteries by using cutting-edge technology to measure momentum, friction and the laws of gravity (Sport Science website). Brenkus often wires himself up and steps in the line of fire against pro athletes to see how a “normal” guy stacks up against the pros (human crash-test dummy video).
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Friday, November 19, 2010
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Tomasz Skwarnicki
[Host: Brad Cox]
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4:00 PM, Room 204
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Syracuse University |
| Physics Building |
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“Status of LHCb Experiment” |
ABSTRACT:
| LHCb experiment is dedicated to searches for new forces in decays of heavy flavors. I will give an introduction to its physics program. I will discuss the detector performance as measured on the first data, present first results and make projections to near and further future. |
Joint Chemistry-Physics Colloquium
ABSTRACT:
| CaF is as “not-atom” as a diatomic molecule can be. The core-penetrating and core-nonpenetrating Rydberg states of CaF are observed by two-color Resonance Enhanced Ionization spectroscopy. The observed rovibronic energy levels are input to an energy- and internuclear distance-dependent Multichannel Quantum Defect Theory fit model. The fitted quantum defect matrix, μ(E,R), accounts for nearly all spectra and dynamics of CaF. A “zone of death” is observed, where selection-rule-shattering “indirect” interactions of all Rydberg states with each other, is caused by one repulsive electronic potential curve. A STIRAP-like, multiphoton, chirped pulse, millimeter wave scheme for “jumping over” this zone of death is being developed. Progress toward “pure electronic spectroscopy” and magnetic resonance-like manipulation of molecular Rydberg states requires taking a step that Arthur Schawlow would have liked, back from CaF, with its one atom too many, to the Ca atom. 5 kilo-Debye Rydberg-Rydberg transitions in Ca are directly detected by Free Induction Decay signals, rather than indirectly, via ions or UV fluorescence, in a pulsed supersonic jet. |
ABSTRACT:
The world faces serious energy issues, and while nuclear energy could in principle address base-line needs, current methods intrinsically link it to proliferation, waste, high-construction cost, and safety issues.
Advances (as confirmed in the 2010 Department of Energy study) in accelerator technology (e.g. SRF at JLab) now allow neutrons to be reliably generated at low-enough cost that a reactor core with a critical mass of fissile material is no longer required. The combination obviates the historical incremental approach to nuclear energy being pursued in this country.
The GEM*STAR approach to such an Accelerator Driven System (ADS) thus intrinsically breaks the links to issues which have crippled the
nuclear energy option. It does this by requiring: no enrichment,
no reprocessing, no critical-mass on site; and providing far deeper burning with orders-of-magnitude less releasable radioactivity in its core and resulting in far less final waste. The project will demonstrate electricity cheaper than coal, and could beneficially utilize today's LWR spent fuel producing no additional waste.
Results from the recent workshop on ADS (hosted by VT and JLab) along with the new report from the DOE will be presented. GEM*STAR is a project of ADNA Corp. and the Virginia GEM*STAR Consortium (VCU, VT, JLab, UVA).
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ABSTRACT:
Quantum computing has attracted much attention over the past sesquidecade because it makes integer-factoring easy, even though that has been a historically (if not provably) hard mathematical problem [1]. Another major interest is the exponential speedup of quantum simulations [2]. The physical implementation of nontrivial quantum computing is an exciting, if daunting, experimental challenge, epitomized by the issues of decoherence and scalability of the quantum registers and processors. In this talk, I will present a novel scheme for realizing a scalable quantum register of potentially very large size, entangled in a "cluster" state, in a remarkably compact physical system: the optical frequency comb (OFC) defined by the eigenmodes of a single optical resonator. The classical OFC is well known as implemented by the femtosecond, carrier-envelope-phase- and mode-locked lasers which have redefined time/frequency metrology and ultraprecise measurements in recent years [3,4]. The quantum version of the OFC is then a set of harmonic oscillators, or "Qmodes," whose amplitude and phase are analogues of the position and momentum mechanical observables. The quantum manipulation of these continuous variables for one or two Qmodes is a mature field. Recently, we have shown theoretically that the nonlinear optical medium of a single optical parametric oscillator (OPO) can be engineered, in a sophisticated but already demonstrated manner, so as to entangle, in constant time, the OPO's OFC into a cluster state of arbitrary size, suitable for one-way quantum computing over continuous variables [5,6]. I will describe the mathematical proof of this result and report on our progress towards its experimental implementation at the University of Virginia.
[1] P. W. Shor, “Algorithms for quantum computation: discrete logarithms and factoring,” in Proceedings, 35th Annual Symposium on Foundations of Computer Science, S. Goldwasser, ed., pp. 124–134 (IEEE Press, Los Alamitos, CA, Santa Fe, NM, 1994).
[2] R. P. Feynman, “Simulating Physics With Computers,” Int. J. Theor. Phys. 21, 467 (1982).
[3] J. L. Hall, “Nobel Lecture: Defining and measuring optical frequencies,” Rev. Mod. Phys. 78, 1279 (2006)
[4] T. W. Hänsch, “Nobel Lecture: Passion for precision,” Rev. Mod. Phys. 78, 1297 (2006).
[5] N. C. Menicucci, S. T. Flammia, and O. Pfister, “One-way quantum computing in the optical frequency comb,” Phys. Rev. Lett. 101, 130501 (2008).
[6] S. T. Flammia, N. C. Menicucci, and O. Pfister, “The optical frequency comb as a one-way quantum computer,” J. Phys. B, 42, 114009 (2009).
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Friday, October 15, 2010
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Brian Winer
[Host: Chris Neu ]
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4:00 PM, Room 204
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Ohio State University |
| Physics Building |
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“Exploring the Universe with Gamma-Rays” |
ABSTRACT:
| The most energetic phenomena in the cosmos are often revealed through their gamma-ray emissions. Observing gamma-rays up to ~100 GeV requires a space-born observatory. The Fermi Gamma-Ray Space Telescope
(FGST) was launched in June 2008 and is beginning its third year of observation of a mission that will last at least 5 years. The primary instrument on FGST is the Large Area Telescope (LAT), which is sensitive to gamma rays from ~20 MeV to over 300 GeV. The current status of the Fermi mission will be discussed along with results from a variety of astrophysical topics including the search for indirect evidence of dark matter.
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Friday, October 8, 2010
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Despina Louca
[Host: Joe Poon]
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4:00 PM, Room 204
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University of Virginia |
| Physics Building |
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“Materials world under scrutiny: the view using a very powerful probe” |
ABSTRACT:
| The emergence of unique physical properties in solids is a manifestation of the coexistence and competition of several degrees of freedom. They are probed by neutrons which provide details on the structure and dynamics. Examples of systems that will be discussed include the magnetoresistive perovskite oxides, bulk metallic alloys, and the new class of superconductors. Understanding the macroscopic functionality of these systems can be potentially very useful for industrial applications. |
ABSTRACT:
| J.J. Suh, a political scientist, and S.-H. Lee, a physicist, have been working together to find out what really happened to the South Korean (SK) Navy corvette, the Cheonan, that sank on March 26, 2010 in the Yellow Sea near the sea border with North Korea. On May 20 after almost two months of investigation, the SK-appointed Joint Investigation Group concluded that the Cheonan had been destroyed by a North Korean torpedo. Our close examination of the JIG's evidence, however, shows that its conclusion is scientifically untenable and that the integrity of some of its scientific data has been compromised.
This episode clearly illustrates the need of interaction and collaboration between social science and natural science experts when science gets entangled with politics, as it often does in this technologically ever-developing world.
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Friday, September 24, 2010
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Sebastian Kuhn
[Host: Don Crabb]
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4:00 PM, Room 204
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Old Dominion University |
| Physics Building |
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“The Jefferson Lab Program on Inclusive and Semi-Inclusive Deep Inelastic Scattering” |
ABSTRACT:
| Nucleons (protons and neutrons) play a dual role as the building blocks of atomic nuclei (which constitute nearly all of the mass visible around us) and as stable systems bound by the fundamental strong force of Quantum ChromoDynamics (QCD). When studied with the most powerful microscopes (accelerators) on Earth, nucleons appear as a chaotic jumble of a nearly infinite number of “partons” (quarks, antiquarks and gluons). However, at the more moderate resolution available at Jefferson Lab, a simpler picture emerges: the quantum numbers of the nucleon are due to just three “valence” quarks which carry a large fraction of its energy-momentum, plus a few quark-antiquark pairs and gluons. One of the main research programs at Jefferson Lab is a detailed study of the distribution in space and momentum space of these partons, and their intrinsic spins. Deep inelastic scattering (DIS), where a relatively large momentum and energy is transferred from a scattered electron to the struck nucleon, is a primary tool to unravel this “medium resolution” structure of the nucleon. Additional information becomes available when one detects part of the final-state debris as well as the scattered electron (semi-inclusive DIS). In my talk, I will give some examples of experiments at Jefferson Lab that employ these tools, and explain what we can learn from them. |
ABSTRACT:
| Over the course of the last two decades, neutron reflectometry has become established as an important
structural probe of thin films and multilayered composites, most notably of hydrogenous and magnetic
materials. As an introduction, the basic principles and typical applications of neutron reflectometry are
briefly reviewed. Examples of neutron reflectometry studies of thin film systems of interest in
condensed matter physics, chemical physics, and biophysics are presented. In particular, the scattering
length density (SLD) depth profile along the surface normal, averaged over in plane, can be deduced
from specular neutron reflectivity measurements (wavevector transfer Q normal to the surface). The
SLD profile, in turn, is directly related to the corresponding material composition distribution. Under
favorable conditions, specular neutron reflectometry can resolve variations in the compositional depth
profile on a length scale of the order of a nanometer for a thin film having a single unit repeat, whereas
for a periodic multilayered system, the spatial resolution can approach an Angstrom.
For specular neutron reflection, the complex reflection amplitude or phase associated with an
"unknown" segment of a composite film structure can be determined exactly, using reference segments,
and a subsequent direct inversion can be performed, thereby ensuring, in principle, a unique result [1].
Thus, the phasesensitive
neutron reflection / inversion process results in a realspace
picture without
fitting or any adjustable parameters. We will discuss how, because of the onetoone
correspondence
between the complex reflection amplitude and the SLD, phasesensitive
NR can be viewed, in effect, as
being equivalent to a realspace
imaging process one
in which the inversion computation plays an
analogous role to that of the brain, for instance, in interpreting the optical image of an object focused on
the retina of the eye [2].
In performing phasesensitive
reflectivity measurements in practice, what ultimately limits the accuracy
and spatial resolution of the depth profile are the maximum range of Q attainable and the statistical
uncertainty in the measured reflected intensities. These effects can be analyzed quantitatively [3] and
we will consider the spatial resolution currently possible as well as what can be reasonably expected in
the future with more advanced neutron sources and instrumentation (e.g., employing polychromatic
beams at continuous sources).
Finally, we will critically examine a possible alternative approach to performing neutron reflectivity
measurements, which involves the quantum phenomenon of "Interaction Free Measurement" (IFM) of
the type first proposed by Dicke [4] and realized in rudimentary fashion by Kwiat et al. with visible
light [5]. The scheme utilized by Kwiat et al. purportedly optimizes the efficiency for performing an
IFM of the reflectivity (or transmission) by application of the quantum Zeno effect (which requires
polarized photons or neutrons) within an interferometer. |
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Friday, April 30, 2010
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Gerald Dunne
[Host: Israel Klich]
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4:00 PM, Room 204
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University of Connecticut |
| Physics Building |
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“The Search for the Heisenberg-Schwinger Effect: Nonperturbative Pair Production from Vacuum” |
ABSTRACT:
| The Heisenberg-Schwinger effect is the non-perturbative production of
electron-positron pairs when an external electric field is applied to
the quantum electrodynamical (QED) vacuum. The inherent instability of the quantum vacuum in an electric field was one of the first non- trivial predictions of QED, but the effect is so weak that it has not yet been directly observed. However, new developments in ultra-high intensity lasers come tantalizingly close to opening a new window on this unexplored extreme ultra-relativistic regime. This necessitates a fresh look at both experimental and theoretical aspects of the Heisenberg-Schwinger effect. I review the basic physics of the problem and describe some recent theoretical ideas aimed at making this elusive effect observable, by careful shaping of laser pulses. This is an example of an emerging new field using ultra-intense lasers to probe fundamental problems in particle physics, gravity and quantum field theory.
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Friday, April 16, 2010
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Paul Chesler
[Host: Peter Arnold]
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4:00 PM, Room 204
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M.I.T. |
| Physics Building |
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“Applied string theory -- from gravitational collapse to quark-gluon liquids” |
ABSTRACT:
| A remarkable result from heavy ion collisions at the Relativistic Heavy Ion Collider is that shortly after a collision, the medium produced behaves as a nearly ideal liquid. The system is very dynamic and evolves from a state of two colliding nuclei to a liquid in a time roughly equivalent to the time it takes light to cross a proton. Understanding the mechanisms behind the rapid approach to a liquid state is a challenging task. In recent years string theory has emerged as a powerful tool to study non-equilibrium phenomena, mapping the (challenging) dynamics of quantum systems onto the dynamics of classical gravitational systems. The creation of a liquid in a quantum theory maps onto the classical process of gravitational collapse and black hole formation. I will describe how one can use techniques borrowed from numerical relativity in astrophysics to study processes which mimic the dynamics of heavy ion collisions.
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ABSTRACT:
| The Casimir self-energy of a boundary is ultraviolet-divergent. In many cases the divergences can be eliminated by methods such as zeta- function regularization or through physical arguments (ultraviolet transparency of the boundary would provide a cutoff). Using the example of a massless scalar field theory with a Dirichlet boundary we explore the relationship between such approaches, with the goal of better understanding the origin of the divergences. We are guided by the insight due to Dowker and Kennedy (1978) and Deutsch and Candelas (1979), that the divergences represent measurable effects that can be interpreted with the aid of the theory of the asymptotic distribution of eigenvalues of the Laplacian first discussed by Weyl. In many cases the Casimir self-energy is the sum of cutoff-dependent (Weyl) terms having geometrical origin, and an "intrinsic" term that is independent of the cutoff. The Weyl terms make a measurable contribution to the physical situation even when regularization methods succeed in isolating the intrinsic part. Regularization methods fail when the Weyl terms and intrinsic parts of the Casimir effect cannot be clearly separated. Specifically, we demonstrate that the Casimir self-energy of a smooth boundary in two dimensions is a sum of two Weyl terms (exhibiting quadratic and logarithmic cutoff dependence), a geometrical term that is independent of cutoff, and a non-geometrical intrinsic term. As by-products we resolve the puzzle of the divergent Casimir force on a ring and correct the sign of the coefficient of linear tension of the Dirichlet line predicted in earlier treatments.
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ABSTRACT:
| There has never been a more exciting time in Particle Physics. The Tevatron scientists are currently mining huge data samples and expect to double the sample yet again before the current run is through.
Meanwhile, the intensity frontier effort is ramping up as Fermilab readies itself for life beyond the energy frontier. In my talk, I will discuss some of the exciting physics results that are currently coming out of the Tevatron program and discuss the future plans of the lab
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ABSTRACT:
| I will begin by motivating the Higgs boson as an important piece of the Standard Model of particle physics that has yet to be experimentally verified. I will then give a short review of high energy colliders and particle detectors and will describe the challenges of discovering a Higgs boson with these machines. I will summarize the status at the Tevatron Collider at Fermilab and the Large Hadron Collider at CERN and portray the excitement at these two labs as the race to discover the Higgs boson tightens up. |
Special Colloquium
ABSTRACT:
| Rare event searches will have a profound impact on the search for physics beyond the Standard Model in the coming years. This is particularly true in searches for neutrinoless double-beta decay and dark matter, and we will discuss one experiment of each type. The MAJORANA experiment will search for neutrinoless double-beta decay in 76Ge by constructing an array of HPGe detectors in ultra-clean electro-formed copper cryostats deep underground. Recent advances in HPGe detector technology, particularly the development of P-type Point Contact (PPC) detectors present excellent new opportunities in identifying and reducing backgrounds to the double-beta decay signal.
The CLEAN/DEAP collaboration is fielding MiniCLEAN, a 400-kg, single-phase detector capable of being filled with either liquid neon or argon. MiniCLEAN uses a spherical geometry to maximize light yield and pulse shape analysis techniques to identify nuclear recoil signals and reject electron recoil backgrounds. Careful attention is being paid to reducing the contamination of detector surfaces by environmental radon gas. We will present an overview and highlight recent R&D progress of both experimental programs.
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Friday, February 26, 2010
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Rocky Kolb
[Host: Peter Arnold]
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4:00 PM, Room 204
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University of Chicago |
| Physics Building |
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“Dark Energy: Taking Sides” |
ABSTRACT:
| Dark energy appears to be the dominant component of the present mass-density of the Universe, yet there is no persuasive theoretical explanation for its existence or magnitude. While the simplest explanation might be Einstein's cosmological constant, there are other possibilities, including dynamical dark energy, modification of general relativity, or back reactions of inhomogeneities.
After framing the dark-energy problem, I will discuss possible theoretical solutions, as well as an observational program to study the properties of dark energy.
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Special Colloquium
ABSTRACT:
| The Standard Model of Particle and Nuclear physics makes thousands of successful predictions, based on roughly 20 experimentally determined input parameters. Studies on the Electroweak frontier in particular require extremely precise values for a subset of those parameters, including the Fermi Constant. I will describe the MuLan experiment, which has measured the muon lifetime with unprecedented part per million accuracy, improving our knowledge of the Fermi Constant by a factor of 20.
I will describe the physics motivation for the measurement, emphasize the subtle design and analysis challenges of a measurement on the precision frontier, and discuss both our published results and current progress towards our ultimate physics goals.
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Special Colloquium
ABSTRACT:
| The discovery just over a decade ago that neutrinos can change identities by oscillating between flavors was a revolutionary change to the Standard Model description of particle physics. This discovery implies that neutrinos are not massless, and that they could play a crucial role in answering some of the most fundamental questions in particle physics, such as whether the observed matter-antimatter asymmetry in the universe can be attributed to CP violating neutrino interactions. Many experiments are currently attempting to solve the remaining mysteries of neutrino behavior, but this is a challenging task due to the elusive nature of these particles. Liquid Argon Time Projection Chambers (LAr TPCs) are ideally suited for the study of neutrino interactions thanks to their precision detection capabilities that make them the modern day equivalent of bubble chambers. In
this talk I will motivate the compelling questions in neutrino physics and introduce the LAr TPC technique, highlighting recent work in the
development of this technology, including discussion of the ArgoNeuT (Argon Neutrino Test) test-beam project and the MicroBooNE experiment.
Finally, I will discuss preliminary ideas for the ultimate experiment that could be conducted at the Deep Underground Science and Engineering Laboratory (DUSEL) in South Dakota as part of a world-class U.S. neutrino program that is currently being planned. |
Special Colloquium
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Wednesday, February 17, 2010
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Jennifer Pursley
[Host: Craig Dukes]
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3:30 PM, Room 204
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University of Wisconsin |
| Physics Building |
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“Searches for a Standard Model Higgs Boson at the Collider Detector at Fermilab” |
ABSTRACT:
| In the standard model of particle physics, the Higgs mechanism is theorized to explain the broken symmetry of the electromagnetic and weak forces by giving mass to the W and Z gauge bosons. One consequence of this theory is the existence of another massive elementary particle, called the Higgs boson.
While this theory of electroweak symmetry breaking was first introduced in the 1960's, the Higgs boson has yet to be observed experimentally and the theory remains unproven. Finding the Higgs boson is currently one of the primary goals of the Fermilab Tevatron collider and the Large Hadron Collider at CERN.
In this colloquium I will start with a brief overview of the standard model of particle physics, the role played by the Higgs mechanism, and previous searches for a Higgs boson. Then I will introduce the Fermilab particle accelerator complex and the Collider Detector at Fermilab experiment, and discuss my own research searching for this elusive piece of the standard model. My focus is on the search for a high-mass Higgs boson, which primarily decays to two W bosons.
Although we have not yet discovered a Higgs boson, at the Tevatron we are narrowing the possibilities. Within a few years we should know whether the standard model Higgs boson exists, or if we need a new solution.
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Friday, January 29, 2010
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Diana Vaman
[Host: Dinko Pocanic]
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4:00 PM, Room 204
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University of Virginia |
| Physics Building |
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“Strings and QCD” |
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Wednesday, January 27, 2010
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Chris Dawson
[Host: Dinko Pocanic]
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3:30 PM, Room 204
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University of Virginia |
| Physics Building |
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“QCD in five dimensions” |
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Friday, January 22, 2010
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Stefan Baessler
[Host: Dinko Pocanic]
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4:00 PM, Room 204
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University of Virginia |
| Physics Building |
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“Why does the (free) neutron decay (?)” |
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Friday, December 4, 2009
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Kambiz Safinya
[Host: Tom Gallagher]
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4:00 PM, Room 204
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Schlumberger Research |
| Physics Building |
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“Meeting Future Energy Demand Through Unconventional Technology ” |
ABSTRACT:
| Crude oil production forecasts point to a drop of 40 M b/d of conventional oil by 2030. Although the financial and economic crisis has driven global energy lower in 2009 for the first time since 1981 on any significant scale, demand will resume its long-term upward trend once the economic recovery gathers pace. By 2030, world primary energy demand is forecast to be around 45% higher than today – this is like adding two more United States to world consumption. There is therefore a drive to develop alternative energy sources as well as unconventional hydrocarbon reserves to replace the lost production from conventional reservoirs. Given that conservative estimates of Heavy Oil reserves approach 6 trillion barrels, and that heavy oil production today is approaching 10% of world production, it is reasonable to suppose that a significant percentage of the production shortfall would be filled through the production of heavy oil. These facts and the significant increase in average crude oil price since the turn of the century have led to an increased level of interest in these types of reservoirs. It is also true that due to the nature of heavy oil, while the reserves are significant, the recoverable reserves are around 5%-7%. The challenge is therefore to develop technologies that can significantly increase the recovery factors of heavy oil reservoirs in an environmentally acceptable manner. This talk will focus on the current approach adopted by industry and the technologies which will be required to address the challenges stated here. |
ABSTRACT:
| As first pointed out by Schrodinger, it is possible to make a "classical"
atom, one in which the electron moves in an orbit around the nucleus, by creating superpositions of stationary quantum eigenstates. In quantum terms the probability has a moving spatial maximum. The idea lay dormant until the mode locked laser allowed the creation of atomic (and molecular) wavepackets. Such wavepackets usually disperse, that is, they lose their spatial localization after a few orbits. Dispersion can be prevented by applying an weak microwave field at the orbital frequency. The microwave field phase locks the electron's orbital motion, and by altering the microwave field it is possible to alter the electron's orbit. For example, increasing or decreasing the microwave frequency increases the orbital frequency, and changing the microwave polarization from linear to circular produces a circular orbit.
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ABSTRACT:
| The first millisecond pulsar was discovered in 1982. Since that time their use as highly-accurate celestial clocks has improved continually, so that they are now regularly used to measure a variety of general relativistic effects and probe a variety of topics in basic physics, such as the equation of state of matter at supra-nuclear densities. One of their most exciting uses though, is the current North American (NANOGrav) and international (the International Pulsar Timing Array) efforts to directly detect nanohertz frequency gravitational waves, most likely originating from the ensemble of supermassive black hole binaries scattered throughout the universe.
In this talk I'll describe how we are using an ensemble of pulsars to try to make such a measurement, how we could make a detection within the next 5-10 years, and how we get a wide variety of very interesting secondary science from the pulsars in the meantime.
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ABSTRACT:
| While entropy was introduced in thermodynamics to describe heat engines, its applications have spread to widely different areas. I will talk about recent research on two such problems. The first is a problem in information theory: how much information can we send over a noisy communication channel, given that the world is described by quantum mechanics? I will explain the so-called "additivity conjecture", which was a proposed way to calculate the communication capacity of such a channel, and I will explain my recent result disproving this conjecture, showing that we can use entanglement to boost communication capacity. The second problem is in quantum systems far from equilbrium. Here I will describe how entropy can arise from quantum entanglement, and I will discuss novel simulation algorithms and future experiments probing the relaxation back to local thermal equilibrium. |
ABSTRACT:
| Mankind has had a long obsession with the quest for limitless or virtually limitless sources of energy. This quest did not stop with the advent of modern physics, but much of it moved out of the realm of science and into the realm of pseudo-science. Today, "free energy" is a thriving, multi-million dollar business. It involves a colorful cast of characters that range from the sincerely self-deluded to outright charlatans. The fact their claims are given greeted with such credulity by both the public and the news media has profound implications about the general state of scientific understanding in our society. |
ABSTRACT:
| Dark energy dominates the expansion of the universe and will determine
its ultimate fate. The best complement to cosmic microwave background
data for constraining the nature of dark energy is an accurate
measurement of the current expansion rate (Hubble constant). The goal
of the Megamaser Cosmology Project is to measure the Hubble constant
by using the Green Bank Telescope and the Very Long Baseline Array to
discover and image 22 GHz water masers orbiting the nuclei of Seyfert
galaxies. We can show that these compact nuclei contain supermassive
black holes, not just dense clusters of stars, and determine their
masses. In the past year we improved our measurement of the
angular-size distance to the galaxy UGC 3789, imaged four more masing
galaxies, and derived a preliminary estimate for the Hubble constant. |
ABSTRACT:
| Thomas Jefferson National Accelerator Facility (Jefferson Lab) is one of the premier facilities for nuclear and hadronic physics in the world. With high luminosity and high polarization continuous wave electron beams, the 6 GeV physics program has produced exciting results during the past decade. Currently the laboratory is executing an upgrade of the accelerator from 6 GeV to 12 GeV: this project was recommended as the top priority in the most recent US nuclear physics long-range plan. The upgrade, which also includes changes to the experimental facilities, will open new avenues of investigation. Beyond this upgrade Jefferson Lab is preparing the case for a future Electron Ion Collider. |
ABSTRACT:
| The profound discovery of Einstein a century ago, that particles can both be
made from energy and disappear back into energy, inspires the experiments
that provide our knowledge of the smallest building blocks of matter. The
experiments, done at enormous energy and intensity frontier accelerators,
have led to a consistent theory of the origins of our world up to a certain
point. However, at an energy scale not far above what we can attain at
existing accelerators, this picture is predicted to break down. Moreover,
the theory of the very small is intimately connected to cosmology -- the
ultimate cause and structure of our universe. Cosmological observations
again point to the need for a new theory in this energy range. In this
colloquium, I will trace out the path from where we are and what we need to
do to take the next step towards understanding the nature of space and time.
The discovery of new particles or new laws at energy and intensity frontier
accelerators will open up windows on this world.
|
|
Friday, May 1, 2009
|
|
Zlatko Tesanovic
[Host: Seunghun Lee]
|
|
4:00 PM, Room 204
|
|
Johns Hopkins University |
| Physics Building |
|
“Superconductivity at the Dawn of the Iron Age” |
ABSTRACT:
| Recent discovery of iron-based high temperature superconductors hints at a new pathway to the room temperature superconductivity. The new materials feature FeAs layers instead of the signature CuO2 planes of much-studied cuprate superconductors. The antiferromagnetism also appears to be involved, although the d-electrons in FeAs seem considerably more mobile than their cuprate cousins. This high mobility, facilitated by a large overlap between atomic orbitals of Fe and As, plays a crucial role in warding off Hund's rule and the large local moment magnetism of Fe ions, the archrival of superconductivity. I will present a pedagogical review of the current status of the field, highlighting similarities and differences between iron pnictides and cuprates, and emphasizing the importance of the multiband nature of magnetism and superconductivity in these new materials.
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|
Friday, April 24, 2009
|
|
George Gollin
[Host: Craig Dukes ]
|
|
4:00 PM, Room 204
|
|
University of Illinois |
| Physics Building |
|
“Academic Fraud and a Calculus of Death” |
ABSTRACT:
| For a price, it is possible to acquire unearned academic degrees from non-existent universities that market diplomas over the internet. The most sophisticated of these diploma mill cartels, based in Spokane, Washington, used the turmoil in Western Africa to foster the illusion of recognition and accreditation by the Republic of Liberia. But these credentials were obtained through payments to government officials, and were no more legitimate than the supporting web of fake diplomatic missions, schools, accreditors, and credential evaluators created by the "Saint Regis University"
group. Their operation spanned at least eighteen states and twenty-two countries, and their stable of degree mills included over seventy non-existent schools selling degrees in medicine, nursing, nuclear and aeronautical engineering, addiction counseling, and special education, among other fields.
Falsely identifying herself as a Liberian official, the principal owner of St. Regis wrote to the University of Illinois in 2003 threatening legal action over information I had posted to a university web page. The resulting brawl led to a multi-agency federal criminal investigation: prosecutors indicted the owners and staff of St. Regis for mail fraud, wire fraud, money laundering, and bribery of foreign officials in late 2005.
All eight defendants pled guilty; five began serving prison terms in late 2008.
This is a serious issue. The investigation revealed an alarming mix of consumer protection, public safety, and national security issues raised by the activities of the Saint Regis group. In addition, the delay in Liberia's recovery from two decades of civil war, due to the corrupting influences of the St. Regis organization, convolves with Liberia's infant mortality rate in a ghastly calculus of death. And we now see a next-generation diploma mill, having learned from St.
Regis' mistakes, attacking the higher education systems in the two African nations immediately to the west of Darfur.
We are beginning to make progress. New federal legislation intended to begin the long process of obliterating the diploma mill industry is a direct result of the St. Regis case. Several states have also drafted new laws, or otherwise tightened their oversight of degree providers. But it is an international problem of great complexity, and we are slow to respond.
I will tell you stories, all of which are true.
|
ABSTRACT:
| Quantum mechanics plays a crucial, albeit often overlooked, role in our understanding of the Earth's climate. In this talk three well known aspects of quantum mechanics are invoked to present a simple physical picture of what may happen as the concentrations of greenhouse gases such as carbon dioxide continue to increase.
Historical and paleoclimatic records are interpreted with some basic astronomy, fluid mechanics, and the use of fundamental laws of physics such as the conservation of angular momentum. I conclude by discussing some possible ways that theoretical physics might be able to contribute to a deeper understanding of climate change.
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Friday, April 10, 2009
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|
Kirill Shtengel
[Host: Israel Klich]
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|
4:00 PM, Room 204
|
|
UC Riverside |
| Physics Building |
|
“Non-Abelian anyons: New particles for less than a billion” |
ABSTRACT:
| The notion of quantum topological order has been a subject of much interest recently, in part because it falls outside of the well-established Landau paradigm whereby states of matter are classified according to their broken symmetries. Topologically ordered phases cannot be described by any local order parameter, yet they have many peculiar properties clearly distinguishing them from the conventionally disordered phases. For example, in two dimensions, they may support anyonic excitations - the quasiparticles that are neither bosons nor fermions. Moreover, anyons with *non-Abelian* braiding statistics are expected to occur, particularly in the fractional quantum Hall regime.
Interesting in their own right, such systems may also provide a platform for topological quantum computation.
Interferometric experiments are likely to play a crucial role in both determining the non-Abelian nature of these states and in their potential applications for quantum computing. I will discuss solid state interferometers designed to detect such non-Abelian quasiparticle statistics. Should these experiments succeed, such interferometers could also become key elements in a topological quantum computer.
|
ABSTRACT:
| The field of high temperature cuprate superconductivity remains as controversial as ever. Although certain matters have been settled, for instance the symmetry of the order parameter, there is no accepted
microscopic framework for describing these materials. This might seem surprising given their relatively simple electronic structure, but the issues involved touch some of the most fundamental ones facing physics - in particular the problem of how to properly treat strong correlations between electrons. In this talk, I will discuss the progress that has been made, but also the many issues that will have to be resolved before we can say that we have "solved" the cuprate problem.
|
ABSTRACT:
| Interactions between pairs of Rydberg atoms can be so strong that the energy level structure of one atom is dramatically altered by the presence of a second atom 10 microns away. This "Rydberg blockade"
is predicted to allow conditional quantum manipulation of individual atoms based on the quantum state of a distant neighboring atom. When successful, the resulting entanglement process occurs without the atoms experiencing any significant interatomic forces. I will describe experiments at the University of Wisconsin that demonstrate blockade-conditioned coherent evolution of a single Rb atom based on the quantum state of a second atom 11 microns away. Extensions of these ideas to deterministic single atom and single photon sources with atomic ensembles will be presented.
|
ABSTRACT:
| Although there is great excitement in particle physics these days, with the advent of the Large Hadron Collider upon us and the great discoveries we hope it will bring, for the first time in some seventy years there are no plans for any new accelerators to take us to the next energy regime. So we will need to look for tiny indirect signs such as rare particle decays in order to find out what may be lurking beyond what we can directly produce in collisions at particle accelerators. There is a long history of such searches for new physics, a history that predates particle physics itself. I will show how such searches will probe mass scales unobtainable by any conceivable particle accelerator and describe the types of accelerators and experiments that are being planned, in particular a very high-sensitivity search for lepton flavor violation in muon decays. |
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Thursday, March 12, 2009
|
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Nathan Guisinger
[Host: Keith Williams]
|
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2:00 PM, Room 205
|
|
Argonne |
| MEC |
|
“Graphene-Based Electronics” |
|
Friday, February 20, 2009
|
|
Richard York
[Host: Blaine Norum]
|
|
4:00 PM, Room 204
|
|
MSU |
| Physics Building |
|
“FRIB: A New Accelerator Facility for the Production of Radioactive Beams” |
ABSTRACT:
| The 2007 Long Range Plan for Nuclear Science had as one of its highest recommendations the “construction of a Facility for Rare Isotope Beams (FRIB) a world-leading facility for the study of nuclear structure, reactions, and astrophysics. Experiments with the new isotopes produced at FRIB will lead to a comprehensive description of nuclei, elucidate the origin of the elements in the cosmos, provide an understanding of matter in the crust of neutron stars, and establish the scientific foundation for innovative applications of nuclear science to society.” A heavy-ion driver driver linear accelerator (linac) will be used to provide stable beams of >200 MeV/u at beam powers up to 400 kW that will be used to produce rare isotopes. Experiments can be done with rare isotope beams at velocities similar to the linac beam, at near zero velocities after stopping in a gas cell, or at intermediate (0.3 to 10 MeV/u) velocities through reacceleration. An overview of the science and the design proposed for implementation on the campus of Michigan State University leveraging the existing infrastructure will be presented. |
ABSTRACT:
| I will present two research topics of Jefferson Lab: The first topic is focused on a planned precision measurement of the parity violating asymmetry in e-2H deep inelastic scattering (PVDIS). This asymmetry is sensitive to the electroweak neutral coupling $C_{2q}$ of the Standard Model. The experiment (E08-011) has been approved to run from November to December 2009. I will present the progress in the preparation of E08-011, in particular the development of a new fast-counting DAQ system.
The second topic is on the extraction of double and single-target spin asymmetries of pion electro-production using JLab Hall B(CLAS)/EG4 data.
We expect to extract these asymmetries in the very low $Q^2$ region
Q^2<0.1 (GeV/c)^2. These data will provide important inputs to global analyses of the nucleon resonance structure. Preliminary results using a 3 GeV beam and a NH$_3$ target will be presented.
|
ABSTRACT:
| A topological insulator is a material with a bulk excitation gap generated by the spin orbit interaction, which is topologically distinct from an ordinary insulator. This distinction - characterized by a topological invariant - necessitates the existence of gapless metallic states on the sample boundary, which have important implications for electronic
transport. In two
dimensions, the topological insulator is a quantum spin Hall insulator, which
is a close cousin of the integer quantum Hall state. In this talk we
will
outline our theoretical discovery of this phase and describe two recent experiments in which the signatures of this effect have been observed. (1) Transport experiments on HgTe/HgCdTe quantum wells have demonstrated the existence of the edge states predicted for the quantum spin Hall insulator.
(2) Photoemission experiments on the semiconducting alloy Bi_{1-x} Sb_x have observed the signature of the gapless surface states predicted for a three dimensional topological insulator. We will close by arguing that the proximity effect between an ordinary superconductor and a 3D topological insulator leads to a novel two dimensional interface state which may provide a new venue for realizing proposals for topological quantum computation.
|
ABSTRACT:
| I will discuss the discovery and characterization of gravitational bound neutron states. In the previous experiments, the lowest neutron quantum states in the gravitational potential were distinguished and characterized by a measurement of their spatial extent. The future detection of resonant transitions between these neutron quantum states with the help of the GRANIT spectrometer (under construction) promises to give further and more precise information. Here, transitions between different quantum states induced by RF pulses shall be observed. These measurements are not only demonstrations of standard quantum mechanics.
I will discuss applications of these measurements in the search for spin-dependent short-range interactions.
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Friday, November 21, 2008
|
|
Pierre Meystre
[Host: Tom Gallagher]
|
|
4:00 PM, Room 204
|
|
University of Arizona |
| Physics Building |
|
“Cavity optomechanics” |
ABSTRACT:
| Recent experimental advances in laser cooling have brought macroscopic oscillators closer than ever before to operating in the quantum regime.
Fundamental interest in this frontier lies in the fact that quantum mechanics has never been tested at such a macroscopic scale, particularly with respect to counter-intuitive effects such as superposition and entanglement. From a more practical point of view, mechanical oscillators operating in the quantum offer considerable promise as sensors whose precision is fundamentally restricted by quantum mechanics. The talk will present a broad review of the basic principles of the laser cooling of opto-mechanical cantilevers, and then turn to a discussion of some possible applications in the coherent control of atomic and molecular systems.
|
ABSTRACT:
| Quantum information science has changed our view of quantum mechanics. Originally viewed as a nag, whose uncertainty principles restrict what we can do, quantum mechanics mechanics is now seen as a liberator, allowing us to do things, such as secure key distribution and efficient computations, that could not be done in the realistic world of classical physics. Yet there is one area, that of quantum limits on high-precision measurements, where the two faces of quantum mechanics remain locked in battle. Using my own career as a convenient backdrop, I will trace the history of quantum-limited measurements, from the use of nonclassical light to improve the phase sensitivity of an interferometer, to the modern perspective on how quantum entanglement can be used to improve measurement precision, and finally to how to do quantum metrology without entanglement.
|
ABSTRACT:
| I will describe results of recent experiments at UVa which have revealed that hydrogen storage upto 14 wt.% can be achieved. This is a world record for hydrogen uptake. I will also review the significant scientific challenges that remain and discuss possible solutions. Related work in other laboratories will be discussed as well.
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Thursday, October 30, 2008
|
|
Seunghun Lee
[Host: Dinko Pocanic]
|
|
4:00 PM, Room 204
|
|
University of Virginia |
| Physics Building |
|
“Magnetic field-induced phase transition in a quantum gapped system: is the Bose-Einstein condensation concept useful?” |
|
Friday, October 24, 2008
|
|
Mark Adams
[Host: Bascom Deaver]
|
|
4:00 PM, Room 204
|
|
Vice President, ITT Corporation |
| Physics Building |
|
“Physics –Fundamentals for Business” |
ABSTRACT:
| Mr. Adams discusses a number of poignant experiences as an undergraduate Physics major at UVA and traces how these lessons have been foundational in his approach to building businesses throughout his career. The technical and operational challenges of remaking a failed $7B company with annual losses exceeding $1B are described from the perspective of a closet physicist. Mr. Adams relates his physics inspired approaches – ranging from the futile to the fruitful – to creating an organization that supports over 300,000 subscribers in over 100 countries worldwide. He also discusses the physics behind his second business startup, which has grown to over a hundred professionals with locations in three states. |
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Friday, October 3, 2008
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Eun-Suk Seo
[Host: Seunghun Lee]
|
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4:00 PM, Room 204
|
|
University of Maryland |
| Physics Building |
|
“Detecting Cosmic Messengers with Antarctic Balloon Flights ” |
ABSTRACT:
| Cosmic rays bring us information about physical processes that accelerate particles to relativistic energies, the effects of those particles in driving dynamical processes in our Galaxy, and the distribution of matter and fields in interstellar space. These cosmic messengers can far exceed the energies produced by man-made particle accelerators on Earth. Balloon-borne instruments configured with particle detectors are flown in Antarctica to study cosmic-ray origin, acceleration and propagation. They are also used to explore a possible supernova acceleration limit and to search for exotic sources such as dark matter and antimatter. Our on-going efforts with balloon-borne experiments will be presented and challenges of extending precision measurements to highest energy practical will be discussed. |
ABSTRACT:
| The past decade has been marked by some remarkable discoveries in the neutrino physics: the particles once believed to be massless have turned out to be massive and have shown evidence of lepton family number violation, as well as other interesting phenomena. While this is exciting, the future may hold even more dramatic discoveries, the hints for which begin to appear in astrophysics and cosmology. The observed neutrino masses imply the existence of some yet undiscovered "right-handed" states, which can be very massive and unreachable, but which can also be light enough to constitute the cosmological dark matter and to account for a number of astrophysical phenomena, from supernova asymmetries and the pulsar kicks to the peculiarities in the reionization and formation of the first stars.
I will review the recent progress in neutrino physics, as well as the clues that may lead to future discoveries.
|
ABSTRACT:
| We often use the term “photon” in reference to individual quantum objects, or particles of light, rather than as excitations of the electromagnetic field. Yet, quantum mechanics textbooks contain no satisfactory wave equation for the photon wave function. I review the analog of the Dirac equation for a photon, which completely describes the evolution of the photon’s quantum wave function in coordinate space. Single photons carry orbital angular momentum as well as spin angular momentum. When a single photon travels in a multimode optical fiber, its spin and orbital angular momenta interact, modifying the shape of the photon wave function as it travels. Close analogy of this behavior can be found with that of an electron in a cylindrical potential, in spite of the fact that a photon has no magnetic moment.
We are carrying out related experiments to illustrate the usefulness of the photon wave function concept.
|
ABSTRACT:
| Over the past decade, molecular magnets or single-molecule magnets
have drawn considerable attention due to observed magnetic quantum
tunneling and interference and a possibility of using them for
information storage or devices. There have been so far significant
efforts to build and characterize thin films or monolayers of
single-molecule magnets on surfaces or single-molecule magnets bridged
between electrodes. However, there is need to understand changes of
the properties of single-molecule magnets in those environments using
atomic-scale simulations. In this regard, we simulate, within
density-functional theory, a nanostructure in which prototype Mn12
molecules are adsorbed via a thiol group onto a gold surface.
Based on a supercell calculation, we investigate how much charge and
spin are transferred between a Mn12 molecule and the metal surface.
In addition, we compare the electronic structure and magnetic
properties of the nanostructure with those of an isolated Mn12 molecule
in the absence and presence of spin-orbit interaction.
|
Joint Astronomy-Physics-NRAO Colloquium
ABSTRACT:
| This question can now be asked because of two results obtained using data recorded at the Pierre Auger Observatory. It has been established, at the 6-sigma level, that the flux of the highest energy cosmic rays is suppressed at energies beyond 5 x 10 19 eV and that above this energy an anisotropy in the arrival directions of the particles is apparent. The arrival directions appear to be associated with sources within the GZK horizon (z ~ 0.018 or 75 Mpc). From these observations it seems probable that we have observed the long-sought Greisen-Zatsepin-Kuzmin effect, demonstrating that ultra-high energy cosmic rays are of extragalactic origin. It is also probable that these particles are protons, thus offering the possibility of insights into features of particle physics at centre-of-mass energies 30 times greater than will be reached at the LHC. Preliminary conclusions from studies of detailed features of extensive air showers suggest that extrapolations from Tevatron energies may not be what have been anticipated hitherto. Much further work remains to be done. |
Hoxton Lecture
|
Thursday, April 17, 2008
|
|
Alan Watson
[Host: Physics Department]
|
|
7:30 PM, Room Chemistry Building, Room 402
|
|
University of Leeds, United Kingdom |
| Physics Building |
|
“The Birth of Cosmic Ray Astronomy on the Argentine Pampas” |
Special Colloquium
|
Tuesday, April 15, 2008
|
|
Daniel Eisenstein
[Host: Dinko Pocanic]
|
|
4:00 PM, Room 204
|
|
University of Arizona |
| Physics Building |
|
“Dark Energy and Cosmic Sound” |
ABSTRACT:
| I present galaxy clustering results from the Sloan Digital Sky Survey that reveal the signature of acoustic oscillations of the photon-baryon fluid in the first million years of the Universe. The
scale of this feature can be computed and hence the detection in the galaxy clustering serves as a standard ruler, giving a geometric distance to a redshift of 0.35. I will discuss the implications of this measurement for the composition of the universe, including dark energy and spatial curvature. I will close with a more general discussion of SDSS-III, a new collaborative project that will feature a large redshift survey
aimed at refining the acoustic oscillation distance scale to 1% as well as surveys for extrasolar planets and the structure of the Milky Way.
|
|
Friday, April 11, 2008
|
|
John Arrington
[Host: Nilanga Liyanage]
|
|
4:00 PM, Room 204
|
|
Argonne National Lab |
| Physics Building |
|
“Nucleon Form Factors...50 Years Later” |
ABSTRACT:
| The structure of the proton and neutron can be expressed in terms of the electric and magnetic form factors which can be measured from elastic electron-proton scattering. Fifty years ago, the first electron scattering measurements of the proton form factors started the process of mapping out the distribution of charge and magnetization of the proton. Four decades of measurements gave us a simple picture of the nucleon, but our understanding was severely limited by the experimental techniques and theoretical understanding. The last ten years as provided several new experimental and theoretical techniques, giving us a much clearer picture of nucleon structure, and providing a few surprises along the way. |
Special Colloquium
|
Monday, April 7, 2008
|
|
Ned Seeman
[Host: Keith Williams]
|
|
4:00 PM, Room Atrium
|
|
NYU |
| Wilsdorf Hall |
|
“Nanoscale Assembly with DNA” |
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Friday, March 28, 2008
|
|
Seonho Choi
[Host: Nilanga Liyanage]
|
|
4:00 PM, Room 204
|
|
Seoul National University |
| Physics Building |
|
“Probing Nucleons Inside Nucleus” |
ABSTRACT:
| The interior world of the nucleus is still a mystery in nuclear physics. While it is well known that the nucleus is made of nucleons, their properties inside the nucleus are still a big puzzle. There has been a series of experiments to probe the nucleons inside the nucleus. However, the results are still controversial. One main remaining question is regarding the Coulomb Sum Rule (CSR). The colloquium will cover the basic concept of probing microscopic world with high energy electron beams, the key issues of the CSR problem and the recent, new experiment at Jefferson Lab to study the CSR problem. |
ABSTRACT:
| One of the most important mysteries in our
understanding of the universe is how elementary particles acquire mass. Our best explanation for this requires the existence of a particle called the Higgs boson, which has not yet been directly observed. Particle physicists at Fermilab, near Chicago, are currently capable of producing and detecting Higgs bosons from collisions of matter and antimatter at very high energies.
I will explain what exactly these physicists are looking for, and present the experimental challenges involved in a few particular methods for differentiating Higgs bosons from other background processes. Finally, I will discuss future prospects for Higgs boson discovery at Fermilab, as well as the discovery potential of future experiments.
|
ABSTRACT:
| Particle physics is at the threshold of an exciting new era. A crucial experimental pursuit is the search for and observation of the Higgs boson, a prominent missing piece in the widely successful standard model of the fundamental world. Searches at the Tevatron proton-antiproton collider in Illinois are closing in on the Higgs, while experiments at the new Large Hadron Collider in Switzerland are scheduled to begin operations later this year. One of the main signatures for the Higgs contains a W boson and one or more b quarks.
However, this signature is shared by more common electroweak and strong processes that have not been determined precisely by experiment until now. Herein I will present a new measurement by CDF of W boson and b quark production. This measurement will contribute to improvements in the theoretical models, and I will discuss how this result can be used to sharpen searches for the Higgs and for physics beyond the standard model at both the Tevatron and the Large Hadron Collider.
|
|
Tuesday, February 19, 2008
|
|
Sabine Lammers
[Host: Brad Cox]
|
|
3:30 PM, Room 204
|
|
Columbia University |
| Physics Building |
|
“The Quest for the SM Higgs” |
ABSTRACT:
| The Standard Model predicts the existence of one final particle, the Higgs Boson, which is the physical manifestation of spontaneous symmetry breaking as a mechanism for electroweak symmetry breaking, and is responsible for the masses of the known gauge bosons. Without the Higgs, the Standard Model is certainly incorrect or at least incomplete. We are at a precipice in the study of particle physics today because the answer to the question of the existence of the Higgs is about to be revealed.
Constraints from precision LEP electroweak data indicate that the Higgs is light, making it within reach of observation by modern high energy particle colliders. I will discuss the state-of-the-art searches for the Standard Model Higgs Boson at the Tevatron and the plans for searches at the LHC. In particular, I will highlight the search techniques that are relevant at each collider and how Higgs searches at the LHC can benefit from knowledge gained at the Tevatron.
|
ABSTRACT:
| Although there has been tremendous progress over the past decade, many basic properties of neutrinos are still unknown and the possibility of future surprises remains strong.
Recent neutrino experiments have conclusively observed that neutrinos have non-zero masses and that neutrinos change from one flavor to another.
The MiniBooNE experiment at Fermilab
recently presented its first neutrino oscillation results, where no significant excess of events was observed at higher energies, but a sizeable excess of events was observed at lower energies. The lack of a significant excess at higher energies allowed MiniBooNE to rule out simple 2-neutrino oscillations as an explanation of the LSND signal; however, the excess at lower energies is presently unexplained. Other data sets, including the NuMI, antineutrino, and SciBooNE data, should allow the collaboration to determine whether the lower-energy excess is due to background or to new physics.
|
ABSTRACT:
| One of the largest remaining questions in particle physics is the
mechanism by which the W and Z bosons gain their mass. In the
Standard Model of Particle Physics, this electroweak symmetry breaking
occurs via the Higgs mechanism, though this remains experimentally
unverified. I will overview this question and then concentrate on how
diboson production and kinematics can give us information about this
symmetry breaking. Experimental studies of boson pairs produced at
the Tevatron and observed at the D0 experiment will be presented,
ending with prospects for further study at the LHC. |
ABSTRACT:
| Living systems are the epitome of self-organized complexity. The self-organization occurs on all scales, from the molecular up to the organismal level. The machines responsible for maintaining organization are protein molecules that receive energy and convert it to work. However, protein molecules themselves must self-organize into highly specific shapes. The folding of proteins is a self-organizing process in which a long chain heteropolymer in a disorganized configuration spontaneously changes its shape to a highly organized structure in milliseconds. I explain how the energy and entropy landscape of protein chains is shaped to allow self-organization. I also show how these principles can be used in molecular level investigations of protein-protein interactions that lead to both beneficial dimerization or disastrous, disease producing and potentially fatal protein aggregation. |
ABSTRACT:
| It is already 21 years since high-temperature superconductivity (HTSC) in the cuprate was discovered by Müller and Bednorz. At the beginning many theoreticians, including several Nobel Laureates, claimed they knew the answer. Even today, they keep claiming so, while they acknowledge that they actually do not know how to solve the problem theoretically. In the mean time experimentalists succeeded in making impressive improvements of their capabilities, and we now know the remarkable details of the cuprates physics and the HTSC phenomena. What emerged from the vast amounts of experimental results is the realization that while the existing theories can describe parts of the observed phenomena, something fundamental appears to be lacking from the theory. The puzzle may be deeper than people prefer to admit. In my view one of the most fundamental problems is that the transition from the Mott-Hubbard insulator due to strong electron-electron interaction to the Fermi-liquid state is an abrupt one, while any mean-field approximation makes it falsely continuous. In this talk I discuss evidences from neutron scattering experiments that this transition involves nano-scale phase separation, reflecting the discontinuity in transition, and how this conflict could contribute to the HTSC phenomena. |
ABSTRACT:
| Advances in experimental technique now allow application of pulsed unidirectional electric fields, termed half-cycle pulses (HCPs), to Rydberg atoms whose characteristic times are much less than the classical electron orbital period. In this limit each HCP simply delivers an impulsive momentum transfer or "kick" to the excited electron. A number of protocols for controlling and manipulating Rydberg atom wavepackets using carefully tailored sequences of HCPs will be described with emphasis on the production of quasi one-dimensional and near circular Rydberg states, on navigating electron wavepackets in phase space, and on studying reversible and irreversible dephasing using electric dipole echoes. Insights provided by this work into classical-quantum correspondence, physics in the ultra-fast ultra-intense regime, and decoherence in mesoscopic quantum systems will be discussed. |
|
Friday, November 9, 2007
|
|
Gabriel Aeppli
[Host: Seung-Hun Lee]
|
|
4:00 PM, Room 204
|
|
University College, London |
| Physics Building |
|
“Entanglement in real magnets” |
ABSTRACT:
| Quantum entanglement is well-known to have consequences for optics and atomic physics, but is less recognized as impacting the properties of solids. Three examples - a dilute rare earth fluoride(Nature 425, 48), a transition metal oxide chain (Science 317, 1049), and a layered organometallic compound (PNAS 104, 15264), where entanglement matters for three real magnets are described. |
|
Friday, November 2, 2007
|
|
Reinhard Schwienhorst
[Host: Bob Hirosky ]
|
|
4:00 PM, Room 204
|
|
MSU |
| Physics Building |
|
“Physics with top quarks” |
ABSTRACT:
| Experimental particle physics has reached a threshold that promises new
and exciting insight into the fundamental structure of matter and the
origin of particle masses in coming years. Due to its large mass, the
top quark plays a key role in this quest for a deeper understanding of
nature. We are currently learning a lot about the top quark through
measurements at the Fermilab Tevatron. At the LHC at Cern, which starts
in 2008, the top quark will become a probe for new physics and a tool
for understanding mass generation. I will present our current
understanding of the top quark and discuss its role in finding the new
physics at the Tevatron and the LHC. |
ABSTRACT:
| The π 0 lifetime has been measured with significantly improved
accuracy at Jefferson Lab using the Primakoff effect. This was
achieved by careful control of all of the experimental parameters and
included auxiliary measurements of the Compton effect and pair
production. This measurement is a test of a prediction based on the
QCD axial anomaly plus few percent chiral corrections which are
proportional to the mass difference of the up and down quarks. The
basic physics, and a comparison of theory and experiment, will be
presented in the context of spontaneous chiral symmetry breaking in
QCD, some of its physical consequences, and other experimental tests.
|
ABSTRACT:
| It has now been seven years since a new era in relativistic heavy ion
research began with the first beams at the Relativistic Heavy Ion Collider
(RHIC). The primary goal of this effort was to heat a small volume of
space so high that normal matter, comprised of protons and neutrons,
dissolves into their constituent parts, the quarks and gluons, thus
possibly creating a quark gluon plasma and perhaps even providing a window
into how the universe may have looked in the first micro-seconds of its
birth. In this talk, I will review the motivation and foundations for
this endeavor, discuss several discoveries since RHIC began, explore a few
of the more recent measurements, and look forward to what the very
exciting and promising future will bring, especially in light of the
startup of the new Large Hadron Collider in CERN. |
|
Friday, October 5, 2007
|
|
Alex Meshik
[Host: Keith Williams]
|
|
4:00 PM, Room 204
|
|
Washington University, St. Louis |
| Physics Building |
|
“Natural Nuclear Reactor in Oklo” |
ABSTRACT:
| Natural nuclear reactors were probably abundant on Earth about 2 billion years ago, but so far only 17 have been found in Equatorial Africa, just a few miles apart from each other. We will talk about how these natural reactors were predicted, searched for and discovered, and how the major characteristics of these reactors have been determined. Then we will show how isotope analyses of fission xenon led to realization of the operational mode of natural reactors and understanding of why the reactors did not explode just after they reached criticality.Finally, we will consider some physical, environmental and geochemical implications of this fascinating natural phenomenon.
|
ABSTRACT:
| The discovery of the metal-insulator transition (MIT) in two-dimensional electron systems challenged the veracity of one of the most influential conjectures in the physics of disordered electrons, which states that "in two dimensions, there are no true metals"; no matter how weak the disorder, electrons would be trapped and unable to conduct a current. However, that theory did not account for electron-electron interactions. Recently, we have investigated the interplay between interactions and disorder near the MIT using simultaneous measurements of electrical resistivity and magnetoconductance. It turns out that both the resistance and interaction amplitude exhibit a fan-like spread as the MIT is crossed. From these data we have constructed a resistance-interaction flow diagram of the MIT that clearly reveals a quantum critical point that separates the metallic state, stabilized by interactions, from the insulating state, where disorder prevails. The metallic side of this diagram is quantitatively described by the recent renormalization group theory (Punnoose and Finkelstein, Science 310, 289 (2005)) without any fitting parameters. |
|
Friday, September 21, 2007
|
|
Ganapati Myneni
[Host: Bellave Shivaram]
|
|
4:00 PM, Room 204
|
|
JLab |
| Physics Building |
|
“JLab Scientific and Technological Advances with Commonwealth of Virginia Universities” |
ABSTRACT:
| The Continuous Electron Bean Accelerator Facility (CEBAF) at Jefferson Lab in Newport News was established by the Department of Energy as a result of the initiatives from the faculty of Physics at the University of Virginia. Initially the design called for room temperature copper accelerator structures. However, the first director of CEBAF chose Superconducting Radio Frequency (SRF) Technology for the acceleration of the high quality electron beams. This led to many world class scientific and technological advances at JLab including the core SRF and 2 K refrigeration systems. In this presentation I would like to narrate the development of single crystal large grain niobium technology for the benefit of SRF accelerator cavities including the Ganni 2 K refrigeration cycle for the efficient cooling of these accelerator structures. Further recent innovations and evolution of 10 - 50 MeV beam test facility, efficient design of cryomodules and compact THz sources are also discussed. In addition the plans of bringing all these scientific and technological advances for the benefit of the commonwealth of Virginia Universities under the umbrella of UVa are also explained. |
ABSTRACT:
| The fascinating history of photography actually extends back more than one millennium, with pre-modern chemical photography finally catching hold around the 1820s through the pioneering work of Niépce and his subsequent collaboration with Daguerre. Viable silver emulsions were developed shortly thereafter by Talbot and others, but it was not until the 1880's that Eastman introduced prototype, flexible films familiar to modern photographers.
At the turn of the last century, Eastman's silver halide films had already revolutionized the art world, opened new doors in optical spectroscopy, and established an entirely new mode of journalism. However, the underlying physical process itself was not understood until the late 1930s, when Mott and Gurney published their theory of latent image formation. Until that point, photographic capabilities were still severely limited because latent images were not stable, and emulsions were still quite slow. J.W. Mitchell established a more comprehensive theory of latent image formation that laid the foundation for improvement. His important contributions defined a turning point in modern film photography, and helped to bring high-performance emulsions to the market, where they have dominated for a half century and are still preferred by many professional photographers today.
This talk will provide a visual review of the past century of photography, providing examples of daguerreotypes, cyanotypes, kalotypes, and modern silver halide photographs in the context of their role in science, art, and journalism. I will also present a brief survey of recent developments in digital image capture and discuss my expectations for advances in the near future.
This memorial colloquium is given in recognition of the contributions J.W. Mitchell, emeritus Professor of Physics at UVa.
|
ABSTRACT:
| Abstract:
At temperatures below 2.176K, liquid He-4 enters into a superfluid state and flows without any friction. The onset of superfluidity is associated with Bose-Einstein condensation where the He-4 atoms, which are bosons, condensed into a single momentum state and acquire quantum mechanical coherence over macroscopic distances. Recent torsional oscillator measurements of solid helium confined in porous media [1,2] and in bulk form [3,4] found evidence of non-classical rotational inertia indicating superfluid behavior below 0.2K. These measurements have been replicated in four other laboratories. Specific heat results will also be discussed. This work is done in collaboration with Eunseong Kim, Tony Clark, Xi Lin and Josh West and it is supported by the (U.S.) National Science Foundation.
|
ABSTRACT:
| The quark-gluon plasma produced in relativistic heavy ion collisions
has been found to behave like a low viscosity fluid whose properties are
very different from those of a weakly interacting gas of quarks and gluons.
It is an example of a strongly coupled, strongly correlated system,
for which perturbative approximation techniques are not adequate.
However, it is now understood that certain 3+1 dimensional gauge theories,
similar to QCD, may be exactly reformulated as string theories in
higher dimensions --- and this "gauge/string duality" is easiest to
use in the strongly coupled limit of the gauge theory. Under this duality,
properties of a high temperature, strongly coupled plasma are directly
related to gravitational dynamics around 4+1 dimensional black holes.
Using this duality, it is possible to compute, reliably, dynamical
properties such as viscosity, energy loss of heavy particles, and
emission spectra in certain strongly coupled gauge theory plasmas.
This talk will describe this progress and discuss its applicability
to the quark-gluon plasma produced in current and upcoming experiments. |
ABSTRACT:
| Ultrafast laser pulses allow us to 'take pictures' of atoms and molecules on their natural timescales (~10 -14 s). They can also be used to exert very strong and controlled forces, allowing us to direct the dynamics of the system they interact with. I will describe a series of experiments which aim to control and measure the wave function for a molecule as it dissociates. The ultimate aims of our efforts are to use shaped laser pulses as 'photonic reagents' and to make 'molecular movies', which depict the evolution of the molecular wave function as a function of time.
|
ABSTRACT:
| The US is heavily involved in the Compact Muon Solenoid (CMS)
experiment at the CERN Large Hadron Colllider (LHC). This new facility is
explicitly designed to successfully search for the Higgs boson and generally
to search for new symmetries of Nature such as Supersymmetry. The status of
the LHC accelerator and the CMS experiment will be discussed as well as
studies of the physics potential of CMS. |
ABSTRACT:
| A new experiment is being planned to search for the neutron
Electric Dipole Moment (EDM) with an unprecedented sensitivity. The proposed
search aims at a two orders of magnitude improvement over
the current experimental limit. A search for a
non-zero value of the neutron EDM is a direct search of the time reversal
symmetry (T) violation. It provides a unique insight into
CP violation because of the CPT theorem. The Standard Model (SM)
prediction for the neutron EDM is below the current experimental limit by six
orders of magnitude. However, many proposed models of electroweak
interaction which are extensions beyond the SM predict much larger
values of neutron EDM. The new experiment has the potential to reduce the
acceptable range of predictions by two orders of magnitude.
Furthermore, if new sources of CP violation are present in nature
beyond the Standard Model and are relevant to hadronic systems,
this experiment offers a
unique opportunity to measure a non-zero value of neutron EDM. The current
understanding of the baryogenesis suggests that other sources of CP violation
might exist in nature beyond the Standard Model and beyond what have been
observed so far. To explain the baryon number asymmetry in the universe through
the grand unified theory or electroweak baryogenesis, substantial New Physics
in the CP violation sector is required. In this talk, I will discuss this new
experiment following a brief review of previous neutron EDM experiments.
|
ABSTRACT:
| The interplay of local and long-range forces in ferromagnets leads to
the formation of mesoscopic domains with sharp boundaries (domain
walls). The physics changes drastically when the magnet size becomes
smaller than the width of a domain wall. In submicron magnets the
magnetization forms intricate smooth patterns that involve the more
exotic topological defects: integer and fractional vortices,
skyrmions,
merons, and magnetic monopoles. I will describe recent experiments
with
these entities and our attempts to describe their static and dynamic
properties. |
ABSTRACT:
| The Cosmic Background Explorer (COBE) satellite, proposed in 1974 and launched by NASA in 1989, measured the cosmic microwave and infrared background radiation from the Big Bang and everything that happened later. The COBE team made three key measurements: the spectrum of the cosmic microwave background radiation (CMBR) matches a blackbody within 50 ppm (rms), the CMBR is anisotropic, with 10 ppm variations on a 7o angular scale, and the cosmic infrared background from previously unknown objects is as bright as all the known classes of galaxies. The first measurement confirmed the Hot Big Bang theory with unprecedented accuracy, the second is interpreted as representing quantum mechanical fluctuations in the primordial soup and the seeds of cosmic structure and the basis for the existence of galaxies, and the third is still not fully understood. I will describe the project history, the team members, the hardware and data processing, the major results, and their implications for science, and end with the outlook for future progress with new background measurements and large telescopes such as the James Webb Space Telescope. I will show recent progress on building the JWST, with illustrations of the key technologies. |
|
Friday, March 16, 2007
|
|
David Weiss
[Host: Tom Gallagher]
|
|
4:00 PM, Room 204
|
|
Penn State University |
| Physics Building |
|
“Quantum simulations and quantum computation with atoms in optical lattices” |
ABSTRACT:
| I will review the physics of 1D Bose gases, show how we experimentally implement them, and describe experiments that confirm the longstanding exact theory across all coupling regimes. I will also describe quantum Newton's cradles, which are out of equilibrium 1D gases that act unlike any other many-body system. Finally, I will show how we image 3D arrays of hundreds of single atoms, an important step on the way to making a neutral atom quantum computer. |
ABSTRACT:
| Nanoscale conductors, such as ultrasmall molecular wires, allow us to test our understanding of fundamental non-equilibrium transport physics, as well as explore new device possibilities. I will start with a generic treatment of current flow through a single energy level, and then generalize to include realistic bandstructure models and a full quantum kinetic theory of current flow. This allows us to interpolate between semi-empirical models that provide quick physical insights, and ‘first-principles’ models with no adjustable parameters. Using this formalism, we can quantitatively explain various experimental features and fundamental performance limits of molecular electronics.
In the above treatments, we treat electrons as weakly interacting, operating in the ‘mean field limit’. However, ultra-short molecules are unique in that they often possess large electronic and vibronic correlation energies with prominent experimental signatures. Strong correlation requires a completely different transport approach in the molecular many-body Fock space that accounts for non-perturbative interactions. I will show that many features such as negative differential resistance, Coulomb Blockade, hysteretic switching and random-telegraph noise can be understood in terms of
the dynamics of such many-body levels and their state filling under bias. A lot of the applications of nanoelectronics could involve bridging the mean-field and strongly correlated regimes, where the theory becomes particularly challenging. For instance, the tunable quantum coupling of current flow
in present day silicon transistors with engineered molecular adsorbates could lead to devices
operating on completely novel principles. |
|
Friday, February 16, 2007
|
|
Carlos Sa de Melo
[Host: Joe Poon]
|
|
4:00 PM, Room 204
|
|
Georgia Tech |
| Physics Building |
|
“The Evolution from BCS to Bose-Einstein Condensation: Superfluidity in Metals, Neutrons Stars, Nuclei, and Ultra-Cold Atoms” |
ABSTRACT:
| > Superfluidity is a very interesting phenomenon that has been found in metals,
> neutron stars, nuclei and more recently in ultra-cold atoms. For a given
> metal, neutron star, or nuclei there is essentially "zero" tunability of the
> particle density or interaction strength, and thus superfluid properties can
> not be controlled at the turn of a knob. However, in ultra-cold Fermi atoms
> the interaction strength and the particle density can be tuned to change
> qualitatively and quantitatively superfluid properties. This tunability allows
> for the study of the evolution from BCS (weak coupling) superfluidity of large
> Cooper pairs to Bose-Einstein condensation (strong coupling) superfluidity of
> tightly bound molecules. I will discuss the BCS to BEC evolution in s-wave
> and p-wave angular momentum channels, and will conclude that this evolution is just a crossover phenomenon for s-wave, while a quantum phase transition takes place for the p-wave case.
|
|
Friday, February 2, 2007
|
|
Sang-Wook Cheong
[Host: Seunghun Lee]
|
|
4:00 PM, Room 204
|
|
Rutgers University |
| Physics Building |
|
“New magnetic twists for multiferroicity” |
|
Friday, January 19, 2007
|
|
Dan Kaplan
[Host: E. Craig Dukes]
|
|
4:00 PM, Room 204
|
|
Illinois Institute of Technology |
| Physics Building |
|
“New Ideas in Neutrino Physics” |
ABSTRACT:
| The existence of neutrinos -- neutral, massless, almost-
noninteracting counterparts of the electron -- was first proposed in
1930, in response to apparently incomprehensible experimental
results. Neutrinos have been a puzzle ever since! One indicator of
their importance is the unusually large number of Nobel prizes
awarded for neutrino work, the most recent in 2002. A brief account
of the neutrino story will lead to a discussion of current issues in
neutrino physics, including the intriguing possibility that neutrino
interactions explain the existence of all matter in the universe.
Techniques for the future study of neutrino physics will be described. |
|
Friday, November 24, 2006
|
|
Thanksgiving Recess
[Host: N/A]
|
|
4:00 PM, Room 204
|
|
N/A |
| Physics Building |
|
“N/A” |
ABSTRACT:
| The standard model of particle physics has been very successful at explaining all collider experiments to date. However, it does not give a
well-motivated explanation for why the electroweak symmetry should be spontaneously broken. Recently several new possible theories have been suggested to cure this shortcoming. I describe the motivations and the consequences of some of these new theories, including large and warped
extra dimensions, higgsless and little higgs models. |
ABSTRACT:
| Superconductivity is a peculiar state of matter which is manifested in such diverse fields as solid state physics, nuclear physics, astrophysics, biology, etc. In this talk we focus on small metallic nanoclusters (N 102-103 where N is the number of free carriers) which contain delocalized electrons. These electrons form shells similar to those in atoms or nuclei. It turns out that under special, but perfectly realistic conditions, superconducting pairing is very strong and can lead to high values of Tc. We have shown that for realistic sets of parameters one can observe very high values of Tc (Tc 102 K ) as well as a strong modification of the energy spectrum. Nanoclusters should form a new family of high temperature superconductors and in principle, it should be possible to raise Tc up to room temperature. We have proposed specific experiments aimed at detecting this phenomenon (e.g. spectroscopy and magnetic properties). This phenomenon is quite promising for the creation of high Tc superconducting tunneling networks. |
ABSTRACT:
| One of the striking differences between the classical world and the quantum world is the measurement process. This opens interesting possibilities to study how a quantum system evolves after a measurement. We have implemented a cavity QED system, where an atom or a few atoms interact with a single mode of the electromagnetic field. This interaction is such that a quantum fluctuation, the emission of a single photon, is a large event. We are studying, by conditional measurements, the dynamics of the cavity QED system as it returns to steady state after a fluctuation and can now relate this to some of its intrinsic properties such as entanglement.
|
|
Tuesday, October 24, 2006
|
|
Seunghun Lee
[Host: Dinko Pocanic]
|
|
3:30 PM, Room 204
|
|
University of Virginia |
| Physics Building |
|
“Almost everything that you'd like to know about frustrated magnets” |
|
Friday, October 13, 2006
|
|
Bill Phillips
[Host: Thomas Gallagher]
|
|
4:00 PM, Room 204
|
|
NIST |
| Physics Building |
|
“"A Bose Condensate in an Optical Lattice: cold atoms meet solid state"” |
ABSTRACT:
| An atomic-gas Bose-Einstein Condensate, placed in the periodic light-shift potential of an optical standing wave, exhibits many features that are similar to the familiar problem of electrons moving in the periodic potential of a solid-state crystal lattice.
Among the differences are that the BEC represents a wavefunction whose coherence extends over the entire lattice, with what is essentially a single quasi momentum and that the lattice potential can be turned on and off or accelerated through space. Experiments that are not easily done with solids are often straightforward with optical lattices, sometimes with surprising results. |
ABSTRACT:
| The year 2005 celebrated the seminal contributions of Albert Einstein to physics, including his treatment of the photoelectric effect and his introduction of the quantum of light. The same year saw Roy Glauber awarded the Nobel Prize in Physics -- ``for his contribution to the quantum theory of optical coherence''. My talk will explore the connections between Glauber's and Einstein's work, while at the same time posing the question...in what sense, exactly, does light act as a particle and not a wave? |
ABSTRACT:
| During a recent term of service on the High Energy Physics Advisory Panel (HEPAP), which jointly advises DOE and NSF on particle physics matters, the speaker was persuaded of the importance of direct participation by active research scientists in the process of federal funding for research and education programs. This view has motivated a temporary term of service by the speaker at the National Science Foundation. The presentation will provide a view of how the NSF conducts its business in Elementary Particle Physics, from the perspective of an university-based experimentalist and faculty member serving as a visiting program officer.
|
|
Friday, September 15, 2006
|
|
Brooks Harris
[Host: Seunghun Lee]
|
|
4:00 PM, Room 204
|
|
University of Pennsylvania |
| Physics Building |
|
“The Unusual Symmetry of Ferroelectricity in Incommensurate Magnets” |
ABSTRACT:
| The coupling between electric and magnetic properties in condensed matter systems is usually very weak. In part this may be viewed as being a result of the fact that the electric and magnetic fields exhibit different symmetries which do not naturally couple to one another. Here I discuss a class of materials which display a very unusual phase transition in which magnetic ordering and the development of ferroelectricity occur simultaneously. This coupling has drawn great interest recently mainly due to various experimental results for this fascinating coupling whereby magnetic ordering induces erroelectricity. My main objective is to understand the phenomonology of this magnetoelectric coupling via a Landau expansion whose consequences depend crucially on the symmetry properties of the magnetic order and the consistency of this order with ferroelectric ordering. Even this simple phenomenological theory explains a number of nontrivial ferroelectric properties which have been observed. I discuss briefly the advantages of such a symmetry analysis versus specific microscopic models. |
|
Friday, September 8, 2006
|
|
Vittorio Celli
[Host: Steve Thornton]
|
|
4:00 PM, Room 204
|
|
University of Virginia |
| Physics Building |
|
“The Ocean Tides: Myth and Truth from Galileo to GPS” |
ABSTRACT:
| It is widely believed, and taught in Physics courses, that two high tides of equal magnitude occur daily. In reality, the tides are a complicated sloshing of the oceans with three main periods: M2 (12.82h) due to the Moon, S2 (12h) due to the Sun, and K1 (23.93h) due to both and to the tilt of the Earth's axis. Following Newton, one can compute the magnitude of the tidal forces, but an understanding of tide dynamics, based on the work of Laplace and Lord Kelvin, is incomplete even today. Over most coastlines M2 is dominant, but in New Orleans, for instance, there is only one high tide each day. In the North Atlantic, the M2 tide runs up the European coast and down the American coast, circling a mid-Ocean point of zero amplitude. This "amphidromic" behavior is seen in many basins, and is due to the Coriolis force acting on tidal currents. Thus, the ocean tides are a direct proof of the Earth's rotation, as Galileo maintained. In fact, his kinematic theory of the "ebb and flow of the waters", based on the Copernican motions of Earth, Sun and Moon, is basically correct, although incomplete. An accurate global picture of tidal amplitudes (but not yet of tidal currents) has been obtained by GPS satellites, and is in turn relevant to space age science and technology.
|
Special Colloquium
|
Tuesday, May 9, 2006
|
|
Daniela C. Rohe
[Host: Nilanga Liyanage]
|
|
3:30 PM, Room 204
|
|
University of Basel, Switzerland |
| Physics Building |
|
“Experiments With Polarized 3He at the Mainz Microtron (MAMI)” |
ABSTRACT:
| Polarized 3He is an interesting target for nuclear physics experiments due to its particular spin structure which allows its use as a polarized neutron as well as polarized proton target. Further, the nucleus is simple enough that exact solutions of its wave function and the reaction channels are available. On the other hand all important interactions between the three nucleons are present and can be studied. Polarization experiments open up new degrees of freedom and find a wide field of application due to their particular sensitivity as well as due to the advantages of asymmetry measurements in general. In this talk I will discuss polarized target technology and will
explain the technique and installation used to
polarize 3He for the nuclear physics target at MAMI. The emphasis of the
talk is on the results achieved so far at MAMI with polarized 3He. Their
purpose is twofold: To test the reliability of the theoretical description
of 3He and to measure the electric form factor of the neutron. An outlook
about ongoing and future research will be given. |
Special Colloquium
|
Thursday, May 4, 2006
|
|
Xiaochao Zheng
[Host: Nilanga Liyanage]
|
|
3:00 PM, Room 205
|
|
MIT |
| Physics Building |
|
“What Have We Learned from Polarized Deep Inelastic Scattering?” |
ABSTRACT:
| Since the 1980's development in polarized electron sources and polarized target techniques has brought the experimental study of the nucleon into a new era: The spin structure of the nucleon has been explored with polarized electron scattering. Now twenty years have passed. What have we
learned from the data? Do they agree with predictions from quantum chromo-dynamics (QCD), the theory for strong interactions? And what about
predictions from constituent quark models?
I will start from an introduction to the study of hadron structure using lepton deep inelastic scattering and give an overview of world data and
what we have already learned about nucleon structure. Then I will present results from a precision experiment completed at Jefferson Lab on the neutron spin in the valence quark region, and discuss about the future of this measurement.
The last 10 minutes of the talk will be devoted to a different topic: using polarized electron scattering to test the electro-weak Standard
Model and hadronic structure, and introducing the PV-DIS program that is being just launched at Jefferson Lab. The talk will be given on an non-expert level.
|
Special Colloquium
|
Monday, May 1, 2006
|
|
Kent Paschke
[Host: Nilanga Liyanage]
|
|
3:30 PM, Room 204
|
|
University of Massachusetts |
| Physics Building |
|
“Using Parity Violation to Probe Strange Quarks in the Nucleon” |
ABSTRACT:
| The basic nuclear building block of our day-to-day world, the nucleon,
is well described in terms of quarks of only two varieties: the up and
down quarks. However, the nucleon is more complex than the apparent
success of the constituent quark model would imply. One example of this
complexity is the possible role of the strange quark in the nucleon.
Precision measurements of parity violation in electron scattering, a
symmetry violation which is forbidden under the electromagnetic
interaction but allowed by the weak force, can be used to disentangle the
contributions of strange quarks from other components of the nucleon
electric and magnetic structure. I will report new results on the most
precise measurement to date of parity-violation in electron-nucleon
scattering, from the HAPPEX collaboration at Thomas Jefferson National
Accelerator Facility, and discuss implications for the question of strange
quarks in the nucleon.
|
|
Friday, April 28, 2006
|
|
Paul C. Canfield
[Host: Seung-Hun Lee]
|
|
4:00 PM, Room 204
|
|
Ames Laboratory and Department of Physics and Astronomy, Iowa State University |
| Physics Building |
|
“The Design, Growth, Discovery and Characterization of Novel Intermetallic Compounds” |
ABSTRACT:
| In this talk I will review the motivations as well as means for the design, growth or search for novel materials. I will provide examples of what physics you can peruse ranging from superconductivity in MgB2, to the spin-glass state in rare earth based quasicrystals, to field induced quantum criticality in Yb-based intermetallics. The emphasis will be on the joy of, and tools for, discovery.
|
Special Colloquium
|
Tuesday, April 25, 2006
|
|
Xiaodong Jiang
[Host: Nilanga Liyanage]
|
|
3:30 PM, Room 204
|
|
Rutgers University |
| Physics Building |
|
“Can Quarks in a Polarized Nucleon Tell Left from Right ?” |
ABSTRACT:
| In the strong interaction, which follows the parity-conserving theory of Quantum Chromodynamics (QCD), can quarks in a polarized nucleon manage to tell left from right ? For "collinear quarks" in a longitudinally polarized nucleon, the answer is simply NO. However, when a nucleon's spin is oriented transverse to it's momentum, quarks inside can figure out left from right through their transverse spin distributions (transversity) and through their angular motions. Recent spin physics experiments from HERMES at DESY and COMPASS at CERN have revealed such an amazing behavior of quarks for the first time, left us with even more questions. Two upcoming Jefferson Lab experiments are designed to provide more answers as to how exactly u- and d-quarks tell left from right in a transversely polarized nucleon. |
|
Friday, April 21, 2006
|
|
Peter Shanahan
[Host: Brad Cox]
|
|
4:00 PM, Room 204
|
|
Fermi National Accelerator Laboratory |
| Physics Building |
|
“Recent Results and Future Prospects in Neutrino Physics” |
ABSTRACT:
| More than 40 years ago, a Nobel Prize winning experiment showed that
neutrinos come in distinct flavors: neutrinos created in association
with muons produced only muons when they interacted, and not electrons.
Over the past decade, however, a series of experiments have established
that the flavor of a neutrino does indeed change with time. The most
likely explanation of this phenomenon is neutrino flavor oscillation,
requiring a finite neutrino mass and therefore an extension of the
Standard Model of Particle Physics. Related physics at energies far
beyond direct experimental reach may well explain the preponderance of
matter over antimatter in the universe. The impact of accelerator-based
experiments in our understanding of neutrino masses and flavor will be
discussed, with an emphasis on current and anticipated experiments at
Fermilab. |
|
Friday, April 14, 2006
|
|
Yuri Gershtein
[Host: Bob Hirosky]
|
|
4:00 PM, Room 204
|
|
Florida State University |
| Physics Building |
|
“News from the Energy Frontier” |
ABSTRACT:
| It is exciting time for particle physics. Currently,
Fermilab's Tevatron, the highest energy accelerator, delivered more than
1 fb-1 to the experiments (CDF and DZero). In just over a year, the
Large Hadron Collider (LHC) at CERN will turn on, moving the energy
frontier by almost an order of magnitude - an event the likes of which
we did not see in almost three decades. I will talk about the
fundamental questions that are addressed by doing physics at the energy
frontier, present some new results from DZero experiment and describe
the status and prospects of the CMS detector at the LHC. |
|
Friday, April 7, 2006
|
|
Oscar Rondon-Aramayo
[Host: Genya Kolomeisky]
|
|
4:00 PM, Room 204
|
|
UVA |
| Physics Building |
|
“Nucleon Structure Studies with Polarized Photons and Polarized Nucleons” |
ABSTRACT:
| The quark and gluon structure of the nucleons (protons and neutrons) was
established by illuminating atomic nuclei with high energy unpolarized real and
virtual photons. The interactions between quarks follow "scaling" rules that
were also established with unpolarized photons. With polarized photons it is
possible to explore the nucleon structure even further. Polarized photons have
been used to determine that quarks carry only 1/3 of the spin, but the
distribution of spin among types ("flavors") of quarks is still under study. And
the "missing" spin carriers are still being investigated. The interactions
between quarks and gluons have barely been explored experimentally. Polarized
photons can also uncover the details of those interactions and relate them to
calculations based on Quantum Chromodynamics - QCD, the fundamental theory of
strong interactions. There is an extensive program of nucleon structure studies
with polarized photons and polarized nuclear targets at Jefferson Lab with the
goal of answering some of these and other related questions. Highlights of the Hall C component of this program will be presented. |
|
Friday, March 31, 2006
|
|
Tom Ferbel
[Host: Bob Hirosky]
|
|
4:00 PM, Room 204
|
|
DOE/University of Rochester |
| Physics Building |
|
“Whither Particle Physics” |
|
Friday, March 24, 2006
|
|
Sally Dawson
[Host: P.Q. Hung]
|
|
4:00 PM, Room 204
|
|
Brookhaven National Laboratory |
| Physics Building |
|
“Adventures at the Terascale” |
ABSTRACT:
| Exciting opportunities are in store for particle physics over the coming
decade, with new tools and experiments poised to explore the frontiers of
high energy, the smallest distance scales, and processes of great rarity.
Einstein's dream of a unification of all forces will be tested at new
energy scales and with greater precision than ever before. The Large
Hadron
Collider at CERN will begin the exploration of higher energy scales than
have been tested previously and a possible future high energy lepton
collider
will continue our explorations.
|
|
Friday, March 17, 2006
|
|
Ralph McNutt
[Host: Blaine Norum]
|
|
4:00 PM, Room 204
|
|
Johns Hopkins University |
| Physics Building |
|
“The MESSENGER Mission to Mercury: Science and Status” |
|
Thursday, March 16, 2006
|
|
David Weiss
[Host: Tom Gallagher]
|
|
4:00 PM, Room 204
|
|
Penn State University |
| Physics Building |
|
|
|
Friday, March 10, 2006
|
|
****SPRING RECESS*****
|
|
4:00 PM, Room 204
|
|
|
| Physics Building |
|
|
|
Friday, February 24, 2006
|
|
Linda Horton
[Host: Despina Louca]
|
|
4:00 PM, Room 204
|
|
ORNL |
| Physics Building |
|
“The Center for Nanophase Materials Sciences” |
ABSTRACT:
| The Center for Nanophase Materials Sciences is the newest user facility at Oak Ridge National Laboratory. Located adjacent to the Spallation Neutron Source, the CNMS is one of 5 nanoscience user facilities being built by the Department of Energy. CNMS is open to scientists and engineers for research to understand the phenomena that control the properties of nanoscale materials. CNMS emphasizes synthesis and characterization, including neutron scattering and electron microscopy. One important capability is a 10,000 sq ft nanofabrication clean room facility. CNMS will also integrate theory and modeling with the experimental program, a critical aspect of the research. The presentation will discuss the capabilities of the new facility, the scientific program, and opportunities for research and collaboration. |
Joint Astronomy-Physics Colloquium
|
Friday, February 17, 2006
|
|
Christopher Stubbs
[Host: Brad Cox]
|
|
4:00 PM, Room 203
|
|
Harvard University |
| Physics Building |
|
“Preliminary Results on the Nature of the Dark Energy from the ESSENCE Supernova Survey ” |
ABSTRACT:
| The discovery of the accelerating expansion of the Universe provides
clear evidence of physics
beyond the standard model. Our current challenge is figuring out what
it means! I will describe the initial results we have obtained in
the ESSENCE supernova survey. This project was designed to detect 200
type Ia supernovae in the redshift range between 0.2 < z < 0.8, with
the goal of measuring the
equation of state parameter of the Dark Energy. We are paying
particular attention to potential sources of systematic
errors that might afflict the measurement, and I will describe some
of the steps we are taking to both control
and quantify these effects.
|
|
Friday, February 3, 2006
|
|
Gail McLaughlin
[Host: Steve Thornton]
|
|
4:00 PM, Room 204
|
|
North Carolina State University |
| Physics Building |
|
“Exploding Stars, Neutrinos, and Nucleosynthesis” |
ABSTRACT:
| The subject of supernovae is a unique combination of many different
branches of physics and there are different ways in which we
can probe the inner workings of these objects. Beyond examining light
curves from the explosion, one can study nucleosynthesis products and
neutrino spectra. The discovery of a whole new type of supernova, one
which creates a gamma ray burst, has created a new frontier in research
on neutrinos and element synthesis. I will discuss the role neutrinos
play in determining whether the heaviest elements, such as uranium and
thorium, are produced in these environments.
|
|
Friday, January 20, 2006
|
|
Art Brill
[Host: Genya Kolomeisky]
|
|
4:00 PM, Room 204
|
|
UVA |
| Physics Building |
|
“Nuclear Spin-Electron Spin Interactions in the Three-Atom System H2N” |
ABSTRACT:
| H2N has one unpaired electron and three nuclei of non-zero spin. The four H2N isotopes from 1H, 2H, 14N and 15N have corresponding sets of hyperfine interactions. Measurements of these constrain calculations of electronic wavefunctions and energies, and provide basic knowledge for application to more complex systems. Nuclear spin-state mixing arises from the off-diagonal elements of the nuclear energy matrix, e.g. Mxx ≡ σκ 〈ψ|Σ (Skzx2kn/r5kn + Sk'zx2k'n/r5k'n|Ψ〉 (Airne and Brill, Phys. Rev.A 63 052511). The principle hyperfine A-values can be expressed in terms of the M’s, e.g. Azz = AFermi - (4/3σ)( Mxx + Myy - 2 Mzz), thereby simplifying the energy matrices. In the absence of nuclear spin-state mixing (i.e. each state pure mI) there are, e.g. 10 epr transitions in D215N and 15 in D214N, all ΔmI = 0 fully allowed. In the presence of mixing there are 243 in D215N and 729 in D214N, with large differences in probability among transitions. Because of numerous, at least partially allowed, overlapping transitions, useful information can be obscured in H2N magnetic resonance spectra. Research is required to arrive at effective experimental conditions. The wide range of transition probabilities will cause H2N resonances to exhibit a corresponding range of microwave power saturation behavior. Simulations display remarkable effects which call for experimental verification by employing a wide range of powers. The nuclear Zeeman interaction (proportional to B) perturbs both the energy and state mixing of nuclear levels, thereby affecting the separation and probability of resonances. Of special interest are the fields Bcross at which pairs of hyperfine levels draw closest. A spectrometer with microwave frequency scanning at fixed B would be useful for centers like H2N in which on-diagonal hyperfine energy matrix elements depend significantly upon B. |
|
Friday, December 2, 2005
|
|
Roger Rusach
[Host: Brad Cox]
|
|
4:00 PM, Room 204
|
|
University of Minnesota |
| Physics Building |
|
“Physics and the CMS Detector at the CERN Large Hadron Collider” |
ABSTRACT:
| In 2007 a new proton-proton collider, the LHC, will turn on and a whole new
energy domain will become accessible to experiment. Indications of what we
might observe come from current measurements in experiments in high-energy
physics, astrophysics and cosmology. We will discuss what problems in
physics might be resolved with data from the LHC, describe how the detectors
work and what are the special challenges associated with building a detector
of the scale required for this energy region. |
|
Friday, November 25, 2005
|
|
****THANKSGIVING BREAK****
|
|
4:00 PM, Room 204
|
|
|
| Physics Building |
|
|
|
Friday, November 18, 2005
|
|
Joe Poon
[Host: Genya Kolomeisky]
|
|
4:00 PM, Room 204
|
|
UVA |
| Physics Building |
|
“Glassy Metals – Complexity Made Simpler ” |
ABSTRACT:
| Although ubiquitous in nature and technology, the microscopic study of liquids and glasses lags far behind that of crystals and quasicrystals. This is because liquids and glasses do not exhibit long-range order, which frustrates theoretical description. To date, the common approaches for modeling the dynamics and glass transition of liquids are based on the potential energy landscape paradigm. Theoretical approaches such as the mode-coupling theory and replica method, although successful in advancing our understanding of the dynamics and thermodynamics of the liquid-glass transition, have not provided specific predictions of the important parameters of the glassy state. Recently, a simple complementary model based on atomic-level fluctuations in the amorphous network has been successfully applied to the computation of these parameters. The latter approach may also provide a pathway to a more general microscopic understanding of liquids and glasses. The rest of this talk will focus on glassy metals as futuristic metals with certain promising and enabling properties.
|
|
Friday, November 11, 2005
|
|
Jeremy Levy
[Host: Joe Poon]
|
|
4:00 PM, Room 204
|
|
University of Pittsburgh |
| Physics Building |
|
“Oxide-Semiconductor Materials for Quantum Computation” |
ABSTRACT:
| Quantum computers, as yet undeveloped, are believed to be able to efficiently solve strategically important problems like number
factorization, database search, and the Schrodinger equation itself. The staggering potential of these and other applications has led to a worldwide race to build the first working quantum computer. The state of experimental
quantum computation is primitive--neither quantum bits (qubits) nor quantum gates (qugates) have been demonstrated in a scalable form. In this talk, I will give an overview of the new field of quantum information science and technology, and will describe a proposal to create a quantum information processor using ferroelectrically coupled electron spins in silicon. This
approach combines the latest advances in nanostructure and heterostructure design, ultrafast optical control, measurement science and signal processing. Progress toward these goals, pursued within the Center for Oxide-Semiconductor Materials for Quantum Computation (COSMQC), will be described.
This work is supported by DARPA QuIST through ARO contract number DAAD-19-01-1-0650. |
|
Friday, November 4, 2005
|
|
Peter Olson
[Host: Keith Williams]
|
|
4:00 PM, Room 204
|
|
John Hopkins University - Earth and Planetary Sciences |
| Physics Building |
|
“Probing the Geodynamo” |
|
Friday, October 28, 2005
|
|
Catherine Brechnigac
[Host: Thomas Gallagher]
|
|
4:00 PM, Room 204
|
|
|
| Physics Building |
|
“Clusters: a route to study stability at nanometer scale” |
|
Friday, October 21, 2005
|
|
Gary Goldstein
[Host: Simonetta Liuti ]
|
|
4:00 PM, Room 204
|
|
Tufts University |
| Physics Building |
|
“The Importance of Spin in Particle Physics” |
|
Friday, October 7, 2005
|
|
Sarah Eno
[Host: Bob Hirosky]
|
|
4:00 PM, Room 204
|
|
University of Maryland |
| Physics Building |
|
“The CMS Experiment” |
This will be a joint Math/Physics/History colloquium.
|
Friday, September 30, 2005
|
|
Mordechai Feingold
[Host: Michael Fowler]
|
|
4:00 PM, Room 203
|
|
Caltech |
| Physics Building |
|
“All Was Light: Isaac Newton's Revolutions” |
|
Friday, September 23, 2005
|
|
William Klemperer
[Host: Thomas Gallagher]
|
|
4:00 PM, Room 204
|
|
Harvard University |
| Physics Building |
|
“The Chemistry of the Universe” |
|
Friday, September 16, 2005
|
|
Chris Morris
[Host: Craig Dukes]
|
|
4:00 PM, Room 204
|
|
Los Alamos National Laboratory |
| Physics Building |
|
“Charge Particle Radiography for National Security” |
ABSTRACT:
| Intermediate energy protons are being used for very fast (flash) radiography.
Proton beams have shown to provide a flexible time format, excellent position resolution,
and adjustable contrast, for a wide range of high explosive driven experiments. These
experiments are playing an increasingly important role in the nuclear stockpile
stewardship program. An outgrowth of this work has been the development of cosmic ray
radiography for cargo and vehicle inspection. An overview of charge particle radiography
and its uses for national security applications will be presented.
|
|
Friday, September 9, 2005
|
|
Doug Osheroff
[Host: Craig Dukes]
|
|
4:00 PM, Room 203
|
|
Stanford University |
| Physics Building |
|
“Understanding The Columbia Shuttle Accident and NASA's Challenges Posed by Discovery” |
ABSTRACT:
| On 1 February 2003 space shuttle Columbia broke up
during re-entry over the plains of East Texas. The speaker was a member
of the board appointed to investigate that disaster. It was ultimately
found that the physical cause of the accident was a piece of thermally
insulating foam that struck the leading edge of the left wing during
launch. This foam had a density of just 1/30th the density of water, yet
it created a hole estimated to be approximately 25 cm square, which
allowed superheated gases to enter the wing on re-entry, consuming the
interior of the wing in a matter of a few minutes. The final report
showed that NASA had that such foam strikes had occurred before, but
continued to fly in the face of clear and persistent danger. The speaker
will also discus the organizational aspects of this accident, many of
which are common to all large organizations, and the future of the
program in light of Discovery's foam shedding.
|
|
Thursday, September 8, 2005
|
|
Thom Mason
[Host: Seunghun Lee]
|
|
4:00 PM, Room 204
|
|
Director, Spallation Neutron Source - Oak Ridge National Laboratory |
| Physics Building |
|
“The Spallation Neutron Source: A Powerful Tool for Materials Research” |
ABSTRACT:
| The wavelengths and energies of thermal and cold neutrons are ideally
matched to the length and energy scales in the materials that underpin
technologies of the present and future: ranging from semiconductors to
magnetic devices, composites to biomaterials and polymers. The
Spallation Neutron Source will use an accelerator to produce the most
intense beams of neutrons in the world when it is complete in 2006. The
project is being built by a collaboration of six U.S. Department of
Energy laboratories. It will serve a diverse community of users drawn
from academia, industry, and government labs with interests in condensed
matter physics, chemistry, engineering materials, biology, and beyond. |
Special Colloquium
[Coffee will be served in Room 205 at 3:30 PM]
|
Tuesday, May 31, 2005
|
|
Professor Theodor Hansch
[Host: Thomas Gallagher]
|
|
4:00 PM, Room 204
|
|
Max Planck Institute for Quantum Optics |
| Physics Building |
|
“Towards a Quantum Laboratory on a Chip” |
|
Friday, May 6, 2005
|
|
Sankar Das Sarma
[Host: Keith Williams]
|
|
4:00 PM, Room 204
|
|
University of MarylandCondensed Matter Theory Center - |
| Physics Building |
|
“Tidbits About Qubits: Spin Computation in Nanostructures” |
ABSTRACT:
| I will provide an introduction to the emerging field of
spintronics and spin qubits in this talk. Active control of carrier spin in
nanostructures of semiconductors and other electronic materials is projected
to lead to new device functionalities in the future. In particular, it may
be possible to envision memory and logic operations being carried out on the
same 'spintronic' chip. I will discuss various aspects of fundamental
physics related to this new research area of spin electronics with the
particular emphasis on localized electron spins in semiconductor
nanostructures, such as GaAs quantum dots and P donors in Si. A
revolutionary possibility in the (perhaps, far) future is using the natural
two-level quantum dynamics of electron spin to create robust quantum bits
('qubits') which could be used to carry out solid state quantum information
processing or quantum computation. I will discuss in details the questions
of entanglement, decoherence, quantum error correction, and quantum gates in
semiconductor nanostructure-based solid state spin quantum computer
architectures, critically discussing from a theoretical perspective the
current status of the field and the prospects for carrying out large-scale
quantum computation using solid state spin qubits. Aspects of fundamental
spin physics in the solid state environment will be emphasized in this talk.
This research has been supported by LPS, ARDA, NSA, ARO, DARPA, ONR, and
Please see http://www.physics.umd.edu/cmtc for the relevant publications.
|
|
Friday, April 29, 2005
|
|
Marina Artuso
[Host: Brad Cox]
|
|
4:00 PM, Room 204
|
|
Syracuse |
| Physics Building |
|
“In Search of New Physics: The Clues From Charm” |
ABSTRACT:
| The study of the interactions between the fundamental
building blocks of matter is a critical component of our understanding
of the history of the universe and its dynamics. My talk will describe
how our experimental study of charm quark decays may test key features
of our present understanding of these interactions, and, possibly, open
a window towards new physics. The experimental data discussed are taken
at the CESR electron-positron collider.
|
|
Friday, April 22, 2005
|
|
Klaus Hon
[Host: Brad Cox]
|
|
4:00 PM, Room 204
|
|
Ohio State University |
| Physics Building |
|
“The Asymmetry Between Matter and Anti Matter - or -How to Know if it is Safe to Shake an Alien's Hand?” |
ABSTRACT:
| Most of us have looked at the spectacular pictures taken by the Hubble Space Telescope. Galaxies, nebulae, super novae -- but there is something peculiar about these images. Where ever we look in space we only see matter. No significant quantities of anti-matter have been found. Since we believe equal amounts of matter and anti-matter have been produced originally we must conclude that there is an asymmetry between particle and anti-particle decays. In the laboratory, however, nature always seems to obey the particle - antiparticle symmetry with one known exception. Almost 40 years ago a small difference has been found in the neutral kaon system. But the nature of this system made it extremely difficult for
both theorists and experimentalists to extract a clear picture of this effect. For years there has been great hope in the particle physics community
that a large matter - antimatter asymmetry can be observed in a new system - the weak decays of massive B mesons. The past decade has seen a vigorous experimental effort to produce the large
quantities of B mesons required to discover the cause of this asymmetry. Particle accelerators have been upgraded and new detectors were
constructed. As we enter the Golden Age of B physics nearly a billion B meson decays have been recorded by these experiments. I will review some
of the old questions that have been answered and discuss some of the new puzzles that have been uncovered. |
|
Friday, April 15, 2005
|
|
Marco Mirazita
[Host: Simonetta Liuti]
|
|
4:00 PM, Room 204
|
|
INFN, Laboratori Nazionali di Frascati |
| Physics Building |
|
“The Search For the Exotic 5 Quark Baryons” |
ABSTRACT:
| All the well established particles can be classified using the
constituent quark model as quark-antiquark states for mesons
and 3-quarks states for baryons.
However, QCD does not forbid the existence of more complicated
internal structures. All the states with quark content different
than quark-antiquark or 3-quarks are called "exotic".
Exotic particles have been searched for many year in the past, but
no positive results have been find until 2003, when several
experimental groups reported the first evidences (even if with low
statistical significance) for an exotic pentaquark state, the
Theta+(1540).
On the other hand, several other experiments did not find positive
evidence for this state, thus suggesting that, if the Theta+ exists,
it should be a really exotic particle.
After these first experimental results, several laboratories planned
new high-statistic experiments, such those performed and presently
under analysis at Jefferson Laboratory.
The aim of these experiments is first of all to confirm the
existence of Theta+(1540), then to set in an unanmbiguous way its
properties.
In this talk, a review of the experimental situation will be given,
and what we need to conclude that the first exotic baryon has been
discovered will be discussed.
|
|
Friday, April 8, 2005
|
|
Al Shapere
[Host: Paul Fendley]
|
|
4:00 PM, Room 204
|
|
University of Kentucky |
| Physics Building |
|
“Production of Microscopic Black Holes by Cosmic Rays” |
ABSTRACT:
| Cosmic ray events may create black holes if extra dimensions exist and are sufficiently large. In particular, neutrino cosmic rays may produce black holes deep in the atmosphere, initiating characteristic quasi-horizontal showers far above the standard model rate. The fact that no such showers have been observed to date places an upper bound on the size of these extra dimensions. Continued nonobservation of such events over the next few years would improve these bounds significantly, and sharply limit the rate of black hole production at LHC. On the other hand, if black hole mediated showers are observed in the next few years, they could provide the first experimental evidence for extra dimensions, string theory, and the formation and decay of microscopic black holes.
|
|
Friday, April 1, 2005
|
|
J. E. Thomas
[Host: Thomas Gallagher]
|
|
4:00 PM, Room 204
|
|
Duke University |
| Physics Building |
|
“High-Temperature Superfluidity in Ultra-Cold Fermi Gases” |
ABSTRACT:
| An optically-trapped Fermi gas of 6Li atoms becomes strongly interacting when it is tuned to a Feshbach scattering resonance. Such a gas is predicted to be a very high temperature superfluid - the transition temperature is a large fraction of the Fermi energy. I will describe experimental evidence for superfluidity which arises in anisotropic expansion of the gas, in the heat capacity, and in collective damping. These cold Fermi gases provide desktop analogs of exotic, strongly-interacting fermions in nature, from high temperature superconductors and neutron stars to quark-gluon plasmas.
|
|
Friday, March 25, 2005
|
|
E. Paschos
[Host: Brad Cox]
|
|
4:00 PM, Room 204
|
|
University of Dortmund, Germany |
| Physics Building |
|
“Planetary Models From the Middle Ages” |
ABSTRACT:
| A small and compact article from AD 1300 describes models for the planets and the moon. It proposes epicyclic theories which deviate from Ptolemy'
s Almagest. The Colloquium reviews the models and their accuracy . Then compares them with Arabic models of that time as well as the Newtonian
theory. It also demonstrates how scientific knowledge was preserved in the Middle Ages and was transmitted to Italy to spark the beginning of the Copernican Rovolution.
|
|
Friday, February 18, 2005
|
|
Rusi P. Taleyarkhan
[Host: Craig Dukes]
|
|
4:00 PM, Room 204
|
|
The Purdue University |
| Physics Building |
|
“Acoustic Inertial Confinement Nuclear Fusion - Status and Challenges” |
ABSTRACT:
| Energetic bubble implosions can generate sonoluminescence (SL) light flashes along with extreme states of compression and temperatures. In cavitation experiments with chilled deuterated acetone, neutron and tritium nuclear emissions were detected, indicative of thermonuclear fusion. The neutron emissions were time correlated with SL light emission. The gamma ray emissions were delayed as would be expected from neutron slowing down and capture. Control experiments with normal acetone did not result in tritium activity or neutron emissions. Fusion was observed during experiments in which the nanoscale nucleation of bubbles was induced in chilled deuterated acetone using a pulse neutron generator as well as with an isotope neutron source. Video images clearly indicate the existing of complex bubble clusters when bubble fusion occurs, and also the formation of comet-like structures which were detrimental to bubble nuclear fusion. Hydrodynamic shock code simulations have supported the experimental findings and indicate temperatures during implosion in the 108K range along with Gbar shock pressures in the imploding bubbles within bubble clusters, but not in single bubble environments. Recent results of experiments will be presented along with discussions related to key technical challenges concerning modeling and experimentation. |
|
Friday, February 11, 2005
|
|
Rich Superfine
[Host: Keith Williams]
|
|
4:00 PM, Room 204
|
|
University of North Carolina |
| Physics Building |
|
“NANOMACHINES: From Atomic Lattice Gears to Cystic Fibrosis” |
ABSTRACT:
| The promise of nanotechnology will be realized through the interplay of new tools and the appreciation of the lessons from biological systems. The challenge of nanomachines ranges from the understanding of the interactions between atomic scale systems to the harnessing of the force generation capabilities of biological systems. We are developing a suite of tools for
nanoscale science including the combination of force measurement and manipulation systems in conjunction with scanning probe, electron and
optical microscopy. For the basic elements of nanomachines, we have studied gears, springs and electrical contacts of carbon nanotubes. Through the study of carbon nanotube dynamics we have observed that atomic lattices can act like gears in promoting the rolling of nanotubes. Most recently, we have begun a study of nanotubes as torsional springs, have measured the torsional
spring constants in freely suspended paddles and have observed strain hardening in individual nanotubes. Finally, biology has developed its own
nanomachines and microfluidic systems that include beating cilia to produce flow and complex closed loop feedback mechanisms. We have begun to study
this system within a cell culture using a new 3D manipulation system, and will discuss our early results in quantifying the forces applied by beating cilia and studies of the resulting flow.
|
Joint Colloquium; Physics-Astronomy. **PLEASE NOTE ROOM NUMBER CHANGE**
|
Friday, February 4, 2005
|
|
Lawrence Krauss
[Host: P.Q. Hung]
|
|
4:00 PM, Room 203
|
|
Case Western Reserve University |
| Physics Building |
|
“Life, the Universe, and Nothing: The Future of Life in an Ever-Expanding Universe” |
ABSTRACT:
| In this talk, I will ruminate on the future of the Universe itself,
and also on the future of life within it, using as
my starting point recent observations in cosmology.
I will first discuss why the Universe we appear to inhabit is the worst of all possible universes, as far as considerations of the quality and quantity
of life is concerned. Then, I will describe how fundamental aspects of the way in which we teach cosmology, in particular the relation between
geometry and destiny, has been forever altered by recent discoveries. Finally, I will address the fascinating question of whether life might be eternal in an eternally expanding universe.
The answer to this question appears to hinge on issues of basic physics, in particular on issues of quantum mechanics and computation, which may determine whether life is ultimately analogue or
digital.
|
|
Friday, January 21, 2005
|
|
C. L. (Lew) Cocke
[Host: Tom Gallagher]
|
|
4:00 PM, Room 204
|
|
Kansas State University |
| Physics Building |
|
“Photon-ion Collisions and Molecular Clocks” |
ABSTRACT:
| The timing of molecular rearrangemnts can be followed in the time domain on a femtosecond scale by using momentum imaging techniques. Three examples will be discussed: First, the diffraction of electrons ejected from the k-shell of one of atomic constituents of the molecule takes a "picture" of the molecule, and the correlation between the momentum vector of the photoelectron and the subsequent fragmentation pattern is used to estimate the time delay which accompanies the latter process. Second, the kinetic energy release of proton pairs from the double ionizaton of hydrogen by fast laser pulses is timed using the 2.7 fs optical cycle as a clock. The mechanisms of rescattering, sequential and enhanced ionization are clearly identified in the momentum spectra. Pump probe experiments allow us to follow the simultaneous propagation of coherently launched wave packets in different exit channels. Third, the operation of rescattering double ionization in the case of nitrogen and oxygen molecules will be discussed. The use of rescattering to probe the structure of the outer orbitals in molecules will be demonstrated. |
|
Friday, December 3, 2004
|
|
Alessandro Drago
[Host: Simonetta Liuti]
|
|
4:00 PM, Room 204
|
|
Universita' degli Studi di Ferrara |
| Physics Building |
|
“Gravitational Waves as a Tool to Investigate Neutron Star Structure” |
ABSTRACT:
| The new generation of Gravitational Wave detectors, including in particular Laser Interferometers as LIGO, is now becoming fully
operative. This will offer the possibility to confirm the existence of the waves predicted by General Relativity and it will also provide the nuclear and astrophysics communities with a new tool to investigate the inner structure of compact stellar objects.
|
|
Friday, November 19, 2004
|
|
Alan Dorsey
[Host: Michael Fowler]
|
|
4:00 PM, Room 204
|
|
University of Florida |
| Physics Building |
|
“Electronic Liquid Crystals: Novel Phases of Electrons in Two Dimensions” |
ABSTRACT:
| There is growing experimental evidence that electrons confined to two dimensions (in a semiconductor heterostructure, for instance) at low temperatures and high magnetic fields
can display a plethora of partially ordered
phases which have the same symmetries as classical liquid crystal phases, such as nematics and
smectics. I will review the experimental evidence for these novel quantum phases of matter, discuss several analogous classical systems, and motivate some of the theoretical models for these "quantum
Hall liquid crystals". |
|
Friday, October 29, 2004
|
|
Frank Moss
[Host: Acar Isin]
|
|
4:00 PM, Room 204
|
|
University of Missouri St. Louis |
| Physics Building |
|
“Random Walks with a Zooplankton” |
ABSTRACT:
| Theories of swarming and pattern formation have recently become of
interest to engineers, chemists and physicists. Interesting examples are
offered by various self-propelled biological agents both in simulations
and in reality. But well-defined swarming experiments in the lab using
real biological agents have been problematic up to now due to size
limitations of the animal groups or lack of precise knowledge of the
agent-agent or agent-medium interactions. We present the results of lab
experiments with the zooplankton /Daphnia/, or “water flea”
intermediate in size and complexity between bacteria and birds or fish,
for example. Our experiments are compared to predictions of the “Active
Brownian Particle” theory developed by a group at Humboldt University in
Berlin. /Daphnia/ show the entire range of the theoretically predicted
behaviors from single agent to collective motions of swarms and can be
observed to perform a fascinating bio-hydrodynamic vortex under certain
conditions.
|
|
Friday, October 22, 2004
|
|
Joel Moore
[Host: Paul Fendley]
|
|
4:00 PM, Room 204
|
|
Berkeley |
| Physics Building |
|
“Hidden Dimensionality in Frustrated Magnets and Complex Superconductors” |
ABSTRACT:
| The idea that the true dimensionality of a system may differ from its superficial dimensionality appears in many areas of modern theoretical physics. A central theme of recent research in correlated electrons is that two- and three-dimensional materials can, in some cases, show exotic physics familiar from one spatial dimension. Quantum phenomena typically restricted to one dimension, like exact self-duality and a vortex-mediated (Kosterlitz-Thouless) phase transition, can appear in dimensions d>=2 as well.
We discuss specific examples of this "dimensional reduction" that are based upon four-spin
interactions generated in frustrated magnets and in effective descriptions of some superconductors. |
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Friday, October 15, 2004
|
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Thomas Cohen
[Host: Simonetta Liuti]
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4:00 PM, Room 204
|
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University of Maryland |
| Physics Building |
|
“The Science and Sociology of Pentaquarks” |
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Friday, October 8, 2004
|
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Professor Shmuel Nussinov
[Host: P.Q. Hung]
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4:00 PM, Room 204
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Tel Aviv University |
| Physics Building |
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“A Physicist Approach to Complex Problems” |
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Friday, October 1, 2004
|
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Jane' Kondev
[Host: Paul Fendley]
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4:00 PM, Room 204
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Brandeis |
| Physics Building |
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“The Physics of Confined DNA” |
ABSTRACT:
| DNA in viruses and in cells is packed in spaces much smaller than its natural size. This state of confinement places interesting constraints on a variety of biological processes DNA is involved in, such as viral infection, gene expression, and recombination. Quantitative experimentation using techniques such as laser tweezers, cryo-electron
microscopy and fluorescence spectroscopy has recently begun to probe in detail the confined state of DNA, both in living cells and in the
test tube. In this talk I will describe this emerging experimental landscape and outline the theoretical challenges it poses. The particular examples I will focus on will be provided by DNA packing in viruses and gene regulation in bacteria. |
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Friday, September 24, 2004
|
|
Milind Diwan
[Host: Brad Cox]
|
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4:00 PM, Room 204
|
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Brookhaven National Lab |
| Physics Building |
|
“New Opportunities in Neutrino Oscillation Physics” |
ABSTRACT:
| I will describe the remarkable new observations that have transformed our knowledge of the neutrino in the past few years. For over 70 years we knew very little about these particles becuase they are so difficult to detect. Now a new consistent picture has emerged about their basic properties. We can now ask new fundamental questions that might bridge the gap between our knowledge of the quarks and the leptons. |
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Friday, September 10, 2004
|
|
Mark Whittle
[Host: Peter Arnold]
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4:00 PM, Room 204
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University of Virginia Astronomy |
| Physics Building |
|
“Primal Scream- Sounds From the Infant Universe” |
ABSTRACT:
| Cosmology's extraordinary development shows no signs of slowing down. With
the evolution of the Universe's average properties now fairly well
understood, the focus has switched to the evoution of perturbations -- how
an extremely smooth infant Universe changes into an extremely lumpy old
Universe, with galaxies strewn to the horizon. Remarkably, the roots of
present day structure can be traced back to sound waves in the early
Universe. Even more remarkable, the power spectrum of the sound shows a
fundamental and harmonics, as if the Universe were a kind of primitive
musical instrument. This talk aims to unpack the relatively new subject
of "Big Bang Acoustics", using reproductions of the primordial sound as a
vehicle for discussing the physics of that remote time. It turns out
that, as with many vibrating objects, the nature of the sound reveals much
about the nature of the object as well as the nature of the stimulus.
|
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Friday, April 23, 2004
|
|
Elliott Lieb
[Host: E. Kolomeisky]
|
|
4:00 PM, Room 204
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Princeton University |
| Physics Building |
|
“The Dilute, Cold Bose Gas: A truly quantum-mechanical many-body problem” |
ABSTRACT:
| The peculiar quantum-mechanical properties of the ground states of Bose
gases that were predicted in the early days of quantum-mechanics have been
verified experimentally relatively recently. The mathematical derivation
of these properties from Schroedinger's equation have also been difficult,
but progress has been made in the last few years (with R. Seiringer,
J-P. Solovej and J. Yngvason) and this will be reviewed. For the low
density gas with finite range interactions these properties include
the leading order term in the ground state energy, the validity of the
Gross-Pitaevskii description in traps, Bose-Einstein condensation and
superfluidity in traps, and the transition from 3-dimensional behavior
to 1-dimensional behavior as the cross-section of the trap decreases. The
latter is a highly quantum-mechanical phenomenon.
For the charged Bose gas at high density, the leading term in the energy
found by Foldy in 1961 for the one-component gas and Dyson's conjecture
of the N^{7/5} law for the two-component gas has also been verified. These
results help justify Bogolubov's 1947 theory of pairing in Bose gases. |
|
Friday, April 16, 2004
|
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Seunghun Lee
[Host: Joe Poon]
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4:00 PM, Room 204
|
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National Institute of Standards and Technology |
| Physics Building |
|
“Unraveling the mysteries in complex oxides by neutron scattering” |
ABSTRACT:
| Neutron scattering is one of the most powerful tools for studying magnetic and structural properties of solids. It has made seminal contributions in a wide range of fields in condensed matter physics and material science, from high Tc superconductivity, colossal magnetoresistance to quantum magnetism. In this talk, I will begin by introducing the basic principles of elastic and inelastic neutron scattering techniques. I will then describe a few exemplary neutron scattering results from high Tc superconductors and quantum magnets that were crucial to understanding the physics of these systems. |
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Friday, April 2, 2004
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Ela Barbaris
[Host: Bob Hirosky]
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4:00 PM, Room 204
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Northeastern University |
| Physics Building |
|
“TBA” |
|
Friday, March 19, 2004
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Dr. Kathleen Turner
|
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4:00 PM, Room 204
|
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Dept of Energy, Office of Science, Office of High Energy Physics |
| Physics Building |
|
“High Energy Physics - On the Ground, Underground, and in Space” |
ABSTRACT:
| The Office of High Energy Physics' mission is to explore the fundamental
nature of matter, energy, space and time. The core of the program centers
on investigations of elementary particles and the interactions between
them using high energy particle accelerators. In order to fully explore
the science, experiments are also done on the ground, underground and in
space. The DOE HEP program provides about 90 percent of the federal
support for high energy physics research in the U.S. and involves over
2,450 researchers at over 100 universities and 8 laboratories. The High
Energy Physics current experimental program will be described, along
with a look towards possibilities for the future.
|
|
Friday, March 5, 2004
|
|
John R. Tucker
[Host: Olivier Pfister]
|
|
4:00 PM, Room 204
|
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Department of Electrical and Computer Engineering - University of Illinois at Urbana-Champaign |
| Physics Building |
|
“Quantum Computers and Atom-Scale Electronics in Silicon” |
ABSTRACT:
| Over the past ten years, my colleague T.-C. Shen and I have developed a process for patterning individual phosphorous donors and self-ordered arrays into silicon with atomic resolution. This technique is now employed by the Australian Centre for Quantum Computer Technology and ourselves in efforts to build a silicon quantum computer. Our current research is focused on developing planar single-electron transistors to probe the quantum states of individual P donor 'qubits' inside the silicon crystal. Thus far, we have demonstrated electron wave interference across a 10nm-linewidth Aharanov-Bohm ring. Prospects for realizing a silicon quantum computer will be outlined, along with additional thoughts on future nanoelectronics and transport experiments. |
|
Friday, February 20, 2004
|
|
Cass Sackett
[Host: Thomas Gallagher]
|
|
4:00 PM, Room 204
|
|
UVA |
| Physics Building |
|
“Atom Interferometry using Bose-Einstein condensates” |
ABSTRACT:
| One of the chief applications envisioned for Bose-Einstein condensation is atom interferometry, in which the wave-like nature of a condensate is used to full advantage. A plethora of uses can be imagined, ranging from inertial sensing to probing surfaces. However, a variety of practical and fundamental obstacles must be overcome before condensate interferometry can be competitive with other techniques, even in a research setting. I will discuss our current understanding of these problems and some possible solutions, and report on progress in our experimental effort to build a condensate interferometer. |
|
Friday, February 13, 2004
|
|
Daniel J. Gauthier
[Host: Olivier Pfister]
|
|
4:00 PM, Room 204
|
|
Duke University - Fitzpatrick Center for Photonics and Communication Systems |
| Physics Building |
|
“Measuring the Information Velocity in Fast- and Slow-Light Media” |
ABSTRACT:
| By all accounts, modern science and engineering has a very good understanding of how to use pulses of light to communicate information. It is, after all, the basis for one of the world's biggest and fastest-growing industries. And yet, the fundamental question of how fast information travels remains unanswered. The engineering community, starting with the seminal work by Shannon, has studied information rates, but has essentially ignored the question of the velocity of information. The physics community, initially prompted by an apparent challenge to Einstein's special theory of relativity, has been debating the issue off and on for almost 100 years. Surprisingly, the issue remains unresolved. There is no clear definition of the information velocity because there is only a vague understanding of where information is contained on a waveform. I will review the information velocity debate and present a technique for experimentally measuring the velocity of information for the case were the group velocity of a pulse of light vastly exceeds the speed of light in vacuum (a so-called "fast-light medium") or is much slower than the speed of light in vacuum (a "slow-light medium"). Our research suggests that the information velocity is equal to the speed of light in vacuum, independent of the characteristics of the medium.
A tutorial on this topic, including links to recent publications, can be found at:
By all accounts, modern science and engineering has a very good understanding of how to use pulses of light to communicate information. It is, after all, the basis for one of the world's biggest and fastest-growing industries. And yet, the fundamental question of how fast information travels remains unanswered. The engineering community, starting with the seminal work by Shannon, has studied information rates, but has essentially ignored the question of the velocity of information. The physics community, initially prompted by an apparent challenge to Einstein's special theory of relativity, has been debating the issue off and on for almost 100 years. Surprisingly, the issue remains unresolved. There is no clear definition of the information velocity because there is only a vague understanding of where information is contained on a waveform. I will review the information velocity debate and present a technique for experimentally measuring the velocity of information for the case were the group velocity of a pulse of light vastly exceeds the speed of light in vacuum (a so-called "fast-light medium") or is much slower than the speed of light in vacuum (a "slow-light medium"). Our research suggests that the information velocity is equal to the speed of light in vacuum, independent of the characteristics of the medium.
A tutorial on this topic, including links to recent publications, can be found at:
http://www.phy.duke.edu/research/photon/qelectron/proj/infv/ |
|
Friday, February 6, 2004
|
|
Jongsoo Yoon
[Host: E. Kolomeisky]
|
|
4:00 PM, Room 204
|
|
UVA |
| Physics Building |
|
“Superconductivity in 2-dimension” |
ABSTRACT:
| Superconductivity occurring in 2-dimension has been understood in the framework of Kosterlitz-Thouless theory, and the nature of the transition is very different from that in 3-dimension. We present our recent data on superconducting properties of ultra-thin tantalum films, and compare with predictions based on the Kosterlitz-Thouless theory. Breakdown of superconductivity near the critical current and new findings on the phenomenon will also be discussed. |
|
Friday, January 30, 2004
|
|
Nilanga Liyanage
[Host: Tom Gallagher]
|
|
4:00 PM, Room 204
|
|
UVA |
| Physics Building |
|
“Precision exploration of neutron spin structure at Jefferson Lab Hall A” |
ABSTRACT:
| Spin structure functions provide basic information about the spin of the quark distributions inside the nucleon. Experimental understanding of the nucleon spin in the kinematic region where the three basic ("valence") quarks dominate the nucleon wave function is still rather poor. Jefferson lab, with its high quality, high polarization continuous electron beam and state of the art polarized nucleon targets in each of its three experimental halls is ideally suited for spin structure measurements in the valence region. An experimental program is underway at Jefferson Lab to measure the spin structure of the nucleon in the valence region with unprecedented precision. The planed upgrade of Jefferson lab CEBAF accelerator to 12 GeV will significantly increase the accessible kinematic range and the precision of these measurements. In this presentation I will give an overview of the neutron spin physics program at Jefferson Lab Hall A. I will also describe new experimental opportunities that will become possible in Hall A with the arrival of 12 GeV beam. |
|
Friday, January 23, 2004
|
|
Debbie Jin
[Host: Thomas Gallagher]
|
|
4:00 PM, Room 204
|
|
Univ. of Colorado |
| Physics Building |
|
“Fun with Fermions: Exploring and Manipulating a Fermi Gas of Atoms” |
|
Friday, January 16, 2004
|
|
John Tranquada
[Host: D. Louca]
|
|
4:00 PM, Room 204
|
|
Brookhaven National Lab. |
| Physics Building |
|
“Superconductors of a Different Stripe: Charge Inhomogeneity and Superconductivity in Copper Oxides” |
ABSTRACT:
| The standard model of electronic structure in solids is founded on the notion
that electrons inevitably delocalize. In contrast, strong Coulomb repulsion in
certain transition-metal oxide compounds can cause electron localization,
resulting in the so-called "Mott-insulator" state. Cuprate superconductors
consist of electronically-doped Mott insulators. Much of the continuing
controversy over how to understand the cuprates concerns the issue of whether
one can apply more or less conventional concepts of delocalized electrons, or
whether radical new concepts are necessary. I will present experimental
evidence, especially from neutron scattering, that the competition been kinetic
and Coulomb energies leads to spatial inhomogeneities of charge carriers and
antiferromagnetic correlations. It is possible that dynamic inhomogeneities
are essential to achieving superconductivity at high temperature. |
|
Friday, December 5, 2003
|
|
Luis Orozco
[Host: Olivier Pfister]
|
|
4:00 PM, Room 204
|
|
U. of Maryland |
| Physics Building |
|
“Conditional Dynamics and quantum feedback; an experiment in cavity QED” |
ABSTRACT:
| Quantum systems that are strongly coupled have fluctuations that
are larger than the average value of their steady state. When the
fluctuation is a single photon, as is the case in cavity QED, the return
to the steady state after the detection of a single photon follows
conditional dynamics measurable with quantum optical correlations. The
conditional dynamics can be modified, via quantum feedback, based on a
single quantum and the knowledge of the conditional state.
Work performed in collaboration with J. E. Reiner, W. P. Smith, M. L.
Terraciano, and H. M. Wiseman with support from NSF and NIST of the USA. |
|
Friday, November 21, 2003
|
|
Collin Broholm
[Host: Despina Louca]
|
|
4:00 PM, Room 204
|
|
John Hopkins University |
| Physics Building |
|
“Quantum Coherence in Magnets” |
ABSTRACT:
Magnetic materials are typically found in one of two qualitatively different states: Thermally disordered at high temperatures or spin ordered at low temperatures. In this talk I describe a third distinct state of an interacting spin system: quantum ordered magnetism. I present neutron scattering data that provide evidence for quantum order in zero, one, two, and three-dimensional spin systems. La4Cu3MoO12 contains spin-trimers that develop quantum order at low temperature where each trimer becomes a composite spin-1/2 degree of freedom. Y2BaNiO5 is an antiferromagnetic spin-1 chain with an extensive one-dimensional Haldane ground state. I present scattering data that provide clear evidence for long range coherence in the absence of conventional spin order2. (C4H12N2)Cu2C16 (PHCC) is a frustrated bi-layer antiferromagnet with interactions that span a two-dimensional plane. I show that there are coherent triplet excitations and argue that competing interactions favor quantum order over spin order3. Cu2(C5H12N2)2Cl4 (CuHpCl) has a cooperative singlet ground state and was initially thought to be a spin ladder. However, neutron scattering data show that it is in fact a three dimensional frustrated system with quantum order. Apart from describing and comparing the low temperature quantum ordered states in these pure systems, I shall also touch on the fascinating effects of impurities5 and the field driven quantum phase transitions that can be accessed experimentally in several of these systems.
REFERENCES
1. Y. Qiu, C. Broholm, S. Ishiwata, M. Azuma, M. Takano, R. Bewley, and W. J. L. Buyers, cond-mat/0205018.
2. Guangyong Xu, J. F. DiTusa, T. Ito, H. Takagi, K. Oka, C. Broholm and G. Aeppli, Phys. Rev. B 54, R6827 (1996).
3. M. B. Stone, I. A. Zaliznyak, Daniel H. Reich, and C. Broholm, Phys. Rev. B 64, 144405 (2001).
4. M. B. Stone, J. Rittner, Y. Chen, H. Yardimci, D. H. Reich, C. Broholm, D. V. Ferraris, and T. Lectka, Phys. Rev. B 65, 064423 (2002).
5. M. Kenzelmann, G. Xu, I. A. Zaliznyak, C. Broholm, J. F. DiTusa, G. Aeppli, T. Ito, K. Oka, and H. Takagi. Phys. Rev. Lett. 90, 087202 (2003).
6. Y. Chen, Z. Honda, A. Zheludev, C. Broholm, K. Katsumata, and S. M. Shapiro Phys. Rev. Lett. 86, 1618 (2001).
|
|
Friday, November 14, 2003
|
|
Peter Arnold
[Host: E. Kolomeisky]
|
|
4:00 PM, Room 204
|
|
UVA |
| Physics Building |
|
“The BEC transition temperature of dilute gases: a not-so-simple problem in statistical mechanics” |
ABSTRACT:
| The phase transition temperature for Bose-Einstein condensation of a
three-dimensional ideal gas of bosons at fixed density is something that every
physicist learns to calculate in graduate school, if not before. Amusingly,
the first correction to that result, from arbitrarily weak interactions, is
sufficiently challenging that only now is there beginning to appear some
theoretical agreement on its magnitude, roughly 80 years after Einstein
computed the ideal gas result. |
|
Friday, November 7, 2003
|
|
Paul Kwiat
[Host: Olivier Pfister]
|
|
4:00 PM, Room 204
|
|
U of Illinois, Urbana-Champaign |
| Physics Building |
|
“Entangled Photons for Quantum Information: 101 uses for a Schroedinger cat” |
ABSTRACT:
| We have developed a means of producing entangled pairs of photons, using the
process of spontaneous parametric downconversion in a novel two-crystal
geometry. The quality of the source has enabled us to produce states of
unparalleled purity, while the brightness has permitted an extreme violation
of Bell's inequalities. Furthermore, the source is tunable, and we have
been able to produce for the first time non-maximally entangled states, and
states of arbitrary purity. The result is the capability to produce
(almost) any two-photon quantum (polarization) state. Such states have
application to such problems in quantum information as quantum cryptography,
quantum teleportation, and quantum cooking. |
Physics and Materials Science Joint Colloquium
|
Friday, October 24, 2003
|
|
Dr. Stuart A. Wolf
[Host: Joe Poon and James Groves]
|
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4:00 PM, Room 204
|
|
University of Virginia, and DARPA at Arlington, VA |
| Physics Building |
|
“A new spin on electronics - spintronics” |
ABSTRACT:
| Until very recently, the spin of the electron was ignored in mainstream electronics. The discovery of the giant magnetoresistance (GMR) effect in magnetic multilayers in 1988 and the subsequent development of sensors based on it began a transformation that will soon provide new paradigms for electronics for the new millenium. This talk will concentrate on the evolution of the DARPA spin electronics or spintronics project. The motivation, the science and the remarkable prospects for the future will be described in some detail. |
|
Friday, October 17, 2003
|
|
Qaisar Shafi
[Host: P. Q. Hung]
|
|
4:00 PM, Room 204
|
|
Bartol Institute |
| Physics Building |
|
“Where does the Standard Model come from” |
ABSTRACT:
| The Standard Model (SM) provides a highly successful description of strong,
weak and electromagnetic interactions at present energies. In combination
with Einstein's general relativity, it helps lay the foundation of another
successful theory, the hot big bang cosmology. Some recent attempts to go
beyond this theoretical framework will be discussed, necessitated in part
by some exciting experimental discoveries, namely neutrino oscillations,
existence of non-baryonic dark matter, CMB anisotropy,etc. |
|
Friday, October 10, 2003
|
|
Herb Fertig
[Host: E. Kolomeisky]
|
|
4:00 PM, Room 204
|
|
University of Kentucky |
| Physics Building |
|
“The Quantum Hall Bilayer: A New Superfluid” |
ABSTRACT:
| Superfluids and superconductors are known to possess a
unique stiffness related to the phase of their groundstate wavefunctions.
Under appropriate circumstances, double layer quantum Hall systems
possess an analogous stiffness that may be understood in terms
of a condensation of particle-hole pairs. The relation between these
systems has motivated both theoretical and experimental efforts
to find properties in the bilayer quantum Hall system usually associated
with superfluids. Most prominently, an effect reminiscent of
Josephson tunneling has been observed in experiments with high quality
samples, although there is considerable dissipation whose origin
is not understood. Using a renormalization group analysis and
results from Langevin dynamics simulations, we demonstrate
that the likely source of dissipation is vortices in the
phase degree of freedom. Vortex pairs are shown to have a
very unusual thermal deconfinement transition in this system, and can
also be broken apart at low temperature by disorder. In the latter
case, simulations show the system possesses properties reminiscent
of a glassy state which qualitatively account for many of the
experimental observations. |
|
Friday, September 12, 2003
|
|
Professor Chris Quigg
[Host: Brad Cox]
|
|
4:00 PM, Room 204
|
|
Fermi National Accelerator Laboratory |
| Physics Building |
|
“Envisioning Particles and Interactions” |
ABSTRACT:
| I will present a new way to envision the particles and interactions: a
pair of interpenetrating tetrahedra that we might call the double
simplex, in homage to the double helix that has just celebrated its
fiftieth anniversary. Any chart or mnemonic device should be an
invitation to narrative and a spur to curiosity, and that is what I
intend for the double simplex. My goal is to represent what we know is
true, what we hope might be true, and what we don't know--in other
terms, to show the connections that are firmly established, those we
believe must be there, and the open issues. I want also to express the
spirit of play, of successive approximations, that animates the way
scientists work.
|
|
Friday, April 25, 2003
|
|
Prof. John Malko
[Host: Oscar Rondon]
|
|
4:00 PM, Room 204
|
|
Emory University |
| Physics Building |
|
“How a doctor of particle physics found happiness working with 'real doctors'” |
SPECIAL PHYSICS AND ASTRONOMY COLLOQUIUM
|
Friday, April 18, 2003
|
|
Tom Abel
[Host: P. Q. Hung]
|
|
4:00 PM, Room 204
|
|
Pennsylvania State Univ. |
| Physics Building |
|
“The First Stars in the Universe” |
ABSTRACT:
| Recent progress in our ability to follow numerically the formation of
the first objects in the universe predict the first stars to massive
and to form in isolation. They are copious producers of UV radiation
and begin to reionize the intergalactic medium. The single currently
allowed model for structure formation turns out to be able to match
all aspects of the most recent accurate measurements of the cosmic
microwave background radiation. In this talk we highlight our new
understanding of the physics of the formation of the first stars,
their lifes, their remnants and their impact on subsequent structure
formation. |
|
Friday, April 11, 2003
|
|
Sean Washburn
[Host: Joseph Poon]
|
|
4:00 PM, Room 204
|
|
University of North Carolina at Chapel Hill |
| Physics Building |
|
“Nanotechnology, nanotubes and molecules as tinker toys” |
ABSTRACT:
| Nanotechnology holds many promises for the future and many (possibly insurmountable) challenges before the promises can be implemented. Carbon nanotubes with their superb mechanical and electrical properties are a canonical example of both of these aspects. The possibility of assembling them into designed forms as new materials or or into nanometer mechanical and electrical devices might lead to improved strengths, speeds, etc. Some elementary experiments indicate that while the promise is still great, the barriers to implementing such nano-devices are still ahead of us. The methods of the experiments already have shown that many academic disciplines and new techniques will be involved in invoking the new improvements. Some examples of such efforts will be reviewed. |
|
Friday, April 4, 2003
|
|
Leslie Camilleri
[Host: Craig Dukes]
|
|
4:00 PM, Room 204
|
|
Fermilab/CERN |
| Physics Building |
|
“The Fascination of Neutrino Oscillations: Their discovery and their future study” |
ABSTRACT:
| Anomalies have been observed in both solar and atmospheric
neutrinos. How the study of these anomalies has led to the discovery of
neutrino oscillations will be summarized. Many experiments are now
being built to further our understanding of these oscillations. These
experiments, and the next generation of experiments being planned to
complete our understanding of how neutrinos mix and what their
mass spectrum is, will be described. |
|
Friday, March 21, 2003
|
|
Ganpathy Murthy
[Host: Eugene Kolomeisky]
|
|
4:00 PM, Room 204
|
|
University of Kentucky |
| Physics Building |
|
“Interactions and Disorder in Quantum Dots: A New Large-g Approach” |
ABSTRACT:
| Understanding the combined effects of disorder and interactions in
electronic systems has emerged as one of the most challenging
theoretical problems in condensed matter physics. It turns out that
one can solve this problem non-perturbatively in both disorder and
interactions in the regime when the system is finite (as in a quantum
dot) but its dimensionless conductance g under open-lead conditions
is large. This regime is experimentally interesting for the statistics
of Coulomb Blockade in quantum dots and persistent currents in rings
threaded by a flux. First some RG work will be described which shows
that a disordered quantum dot with Fermi liquid interactions can be in
one of two phases; one controlled by the so-called Universal
Hamiltonian and another regime where interactions become large. These
two are separated in the infinite-g limit by a second-order phase
transition. I will show how to solve for the strong-coupling phase, which is
characterized by a Fermi surface distortion, by a large-N
approximation (where N=g is in fact large for realistic
systems). Predictions will be presented for finite but large g for
the statistics of the Coulomb Blockade peak spacings and other
correlators. Finally, the relationship of these results to
puzzles in persistent currents in mesoscopic rings will be
presented. |
|
Friday, March 14, 2003
|
|
Dinko Pocanic
[Host: Eugene Kolomiesky]
|
|
4:00 PM, Room 204
|
|
University of Virginia |
| Physics Building |
|
“A new look at rare pion and muon decays” |
ABSTRACT:
Pion and muon, the lightest unstable particles, were discovered more than fifty years ago, and have been well studied since. However, over time the Standard Model (SM) of elementary particles and interactions has become so successful that for several key pion and muon properties its predictions are far less uncertain than the best available measurements, primarily those concerning the particles' rare decay modes. Thus, slight deviations from the SM predictions can provide valuable clues to new physics outside of the current SM.
In its first phase, the PIBETA experiment has measured accurately several such rare decays at PSI, the Swiss meson facility. The talk will focus on the motivation, experimental apparatus, method, and the unexpected first results of these measurements. |
|
Friday, February 21, 2003
|
|
Philip Phillips
[Host: Jongsoo Yoon]
|
|
4:00 PM, Room 204
|
|
UIUC |
| Physics Building |
|
“The Illusive Bose Metal” |
ABSTRACT:
| Cooper pairs (bosons) are thought to exist in two quite distinct ground
states:
1) localized in a Mott insulator or 2) condensed in a superconductor.
However,recent experiments on 2D insulator-superconductor transitions
indicate
that there may be a third possibility: a metal with a finite resistivity
at zero temperature. I will review the standard theoretical framework
used to understand the insulator-superconductor transition, the recent
experimental
results and I will show quite generally how bosons lacking phase
coherence can form
a metal in the presence of disorder rather than an insulating phase.
The metallic state is rather weird,
however. The phase degrees of freedom are glassy. At the heart of the
metallic state is the dissipation inherent in the glassy state.
Bosons moving in such
a glassy environment fail to localise because no true ground state
exists. |
|
Friday, February 14, 2003
|
|
Robert Bryant
[Host: Bascom Deaver]
|
|
4:00 PM, Room 204
|
|
UVA - Chemistry |
| Physics Building |
|
“Nuclear Spin Relaxation, Dispersion, and Intermolecular Exploration” |
|
Friday, February 7, 2003
|
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Rolf Sharenberg
[Host: Ken Nelson]
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4:00 PM, Room 204
|
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Purdue University - (E-735 Collaboration) |
| Physics Building |
|
“Experimental evidence for hadronic deconfinement in pbar-p collisions at 1.8 TeV” |
ABSTRACT:
| We have measured deconfined hadronic volumes, 4.4 < V < 13.0 fm3, produced by a one dimensional (1D) expansion. These volumes are directly proportional to the charged particle pseudorapidity densities 6.75 < dNc/d0 < 20.2. The hadronization temperature is T = 179.5±5(syst) MeV. Using Bjorken's 1D model, the hadronization energy density is F = 1.10±0.26(stat) GeV/fm3 corresponding to an excitation of 24.8±6.2(stat) quark–gluon degrees of freedom. |
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Friday, January 31, 2003
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Amy Bug
[Host: Simonetta Liuti]
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4:00 PM, Room 204
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Swarthmore College |
| Physics Building |
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“Gender and Physics: a Hard Look at a Hard Science” |
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Friday, January 24, 2003
|
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David Divincenzo
[Host: Olivier Pfister]
|
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4:00 PM, Room 204
|
|
IBM |
| Physics Building |
|
“Prospects for Quantum Computation” |
ABSTRACT:
| A "standard model" for the physical implementation of a quantum computer
was laid out some years ago. It indicated a set of capabilities that
had to be achieved to make quantum processing possible: 1) systems with
well-characterized qubits must be constructed. 2) These qubits should be
initializable to the "0" state. 3) It must be possible to control the
one- and two-qubit Hamiltonian of the system, so that unitary quantum
logic gates are enacted. 4) Decoherence and imprecision of gate
operations must be kept very low. 5) Reliable measurements of the
quantum state of individual qubits must be possible. In this talk I
will indicate progress towards these goals, after first reviewing why we
want to do quantum computation. |
|
Friday, November 22, 2002
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David DeMille
[Host: Cass Sackett]
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4:00 PM, Room 204
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Yale |
| Physics Building |
|
“Tabletop probes for TeV physics: searches for the electric dipole moment of the electron” |
ABSTRACT:
| Remarkably, the virtual exchange of exotic heavy particles--such as
those predicted to exist in supersymmetric and grand unified theories--
can lead to observable effects in ordinary matter. This talk will
describe a set of experiments searching for such an effect: namely, a
permanent electric dipole moment along the spin of the electron. The
most sensitive experiments of this type are already sensitive to new
physics at the TeV scale, and set important limits on possible
extensions to the standard model. I will report on our progress
in developing a new technique, which promises several orders of
magnitude improvement in sensitivity. |
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Friday, November 15, 2002
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|
Konstantin Matveev
[Host: Eugene Kolomeisky]
|
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4:00 PM, Room 204
|
|
Duke University |
| Physics Building |
|
“ 0.7-anomaly in Quantum Point Contacts A” |
ABSTRACT:
| A remarkable property of one-dimensional conductors is the
quantization of their resistance in units of Planck constant divided
by the square of the elementary charge. This effect is well
understood and readily observed in low-temperature experiments with
relatively short one-dimensional conductors called the quantum point
contacts. A puzzling feature of the transport through such contacts
was reported a few years ago, when it was discovered that at somewhat
higher temperatures the conduction drops to about 0.7 of its quantized
value. This phenomenon, often referred to as the 0.7-anomaly, has
been studied extensively in the last few years. I will discuss the
latest experimental data and the theoretical attempts at understanding
this effect. |
|
Friday, November 8, 2002
|
|
Jerry Blazey
[Host: Bob Hirosky]
|
|
4:00 PM, Room 204
|
|
NIU |
| Physics Building |
|
“Physics at DZERO: Exploring the Microscopic Structure of the Universe” |
ABSTRACT:
| To explore the microscopic structure of the universe very energetic
beams of submicroscopic particles and complicated detectors, such as the
DZERO detector, are required. These huge machines, built by graduates
students, physicists, and engineers, have the potential to explain the
origins of mass and to explore extra spatial dimensions. The technology
behind these investigations and their current state will be described.
Prof. Blazey serves as spokesman for the D-Zero Collaboration at
Fermilab and director of NICADD, the Northern Illinois Center for
Accelerator and Detector Development. |
|
Friday, October 25, 2002
|
|
Randy Hulet
[Host: Cass Sackett]
|
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4:00 PM, Room 204
|
|
Rice University |
| Physics Building |
|
“Tunable Interactions in Ultracold Bose and Fermi Gases - Solitons to Superfluids” |
ABSTRACT:
| Bose-Einstein condensation of ultracold atomic gases, first achieved
only seven years ago, has lead to remarkable demonstrations of matter
wave phenomena. One of the most compelling aspects of ultracold atoms
is the experimental ability to alter the strength and even the sign of
the interactions between atoms using magnetically tuned "Feshbach
resonances". We have exploited this tunability to create matter wave
solitons composed of Bose-Einstein condensates of lithium atoms [1]. A
similar experiment was performed in Paris [2]. Soliton waves arise when
a nonlinearity exactly compensates for wavepacket dispersion. This
compensation enables a soliton to propagate without spreading. Solitons
are observed in a variety of physical systems, including water waves,
plasma waves, and optical pulses, to name but a few. The nonlinearity
in ultracold atoms arises from their interactions. By changing the
interactions from repulsive to attractive, the condensate is observed to
form a multi-soliton "train" of up to 15 individual solitons. The
solitons maintain their size and shape for a propagation time of up to 3
s. Adjacent solitons are observed to interact repulsively.
We are also pursuing the possibility of creating Cooper pairs of
fermionic 6Li atoms, which would be an atom analog of superconductivity,
in the gas phase. The necessary attraction would again be generated
using a Feshbach resonance, which could enable the first exploration of
superconductivity in the strong coupling regime.
[1] K.E. Strecker, G.B. Partridge, A.G. Truscott, R.G. Hulet Nature 417,
150 (2002).
[2] L. Khaykovich et al., Science 296, 1290 (2002). |
|
Friday, October 18, 2002
|
|
Siyuan Han
[Host: B. Shivaram]
|
|
4:00 PM, Room 204
|
|
Department of Physics and Astronomy, University of Kansas |
| Physics Building |
|
“Superconducting Schrodingers Cat and its Application to Quantum Computing” |
ABSTRACT:
| Since the beginning days of quantum mechanics the
possibility of having coherent superposition of macroscopic quantum
states, e.g., Schrodingers Cat, has stimulated much theoretical
debates. The idea can actually be tested out experimentally in
superconducting electronic devices called Josephson junctions (JJs)
and SQUIDs. Ill show that when sufficiently isolated from
environments a current biased JJ is a very well characterized and
controllable macroscopic quantum system and that Rabi oscillations
can be utilized to create coherent superposition of macroscopic
quantum states. In a recent experiment, we have succeeded in placing
a JJ in the superposition of its ground (alive) and excited (dead)
states and observing its time evolution as it oscillates coherently
between the alive and dead states of the junction [Y. Yu
et al.,
Science 296, p889 (May 2002)]. The coherence time, estimated from
the exponentially decaying amplitude of the oscillations, is about 5
s which is very promising for quantum computing using the phase
qubits (JJs) or flux qubits (SQUIDs). |
|
Friday, October 4, 2002
|
|
Professor Paul Avery
[Host: Brad Cox]
|
|
4:00 PM, Room 204
|
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University of Florida |
| Physics Building |
|
“Global Data Grids for Data Intensive Science” |
|
Friday, September 20, 2002
|
|
Greg Landsberg
[Host: P. Q. Hung]
|
|
4:00 PM, Room 204
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Brown University |
| Physics Building |
|
“Black Holes at Future Colliders and Beyond” |
ABSTRACT:
| If the scale of quantum gravity is as low as a TeV, as was proposed by
Arkani-Hamed, Dimopoulos, and Dvali a few years ago, one of the most
dramatic manifestation of this fact would be copious production of
miniature black holes at the CERN's LHC accelerator, qualifying the
latter as black-hole factories. These rapidly evaporating black holes
could serve as sensitive probes of quantum gravity effects, topology of
extra dimensions, and as a laboratory to produce new particles with the
mass ~100 GeV. I'll discuss the black hole production and decay
mechanisms at future colliders and the opportunities of cosmic ray
detectors in observing black holes in ultra-high-energy cosmic ray
collisions. Using the Higgs boson as an example, I'll demonstrate that
it can be found in the decays of black holes as early as in the first
hour of operation of the LHC, even with incomplete detectors. |
|
Friday, September 13, 2002
|
|
Prof. Puru Jena
[Host: Joseph Poon/Louis Bloomfield]
|
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4:00 PM, Room 204
|
|
Virginia Commonwealth University |
| Physics Building |
|
“The Role of Clusters in the Design of Nano-Scale Systems” |
ABSTRACT:
| Atomic clusters consisting of a few to a few thousand atoms constitute a
new phase of matter intermediate between atoms and solids. Unlike
conventional nanostructured materials, the size and composition of these
clusters can be controlled one atom at a time. The properties of such
clusters brought about by their large surface-to-volume ratio, unique
geometry, low dimensionality and reduced coordination, exhibit novel
behavior quite unlike that in the bulk. For example, metallic elements can
be made to form ionic bonds while nonmagnetic and anti-ferromagnetic
materials can become ferromagnetic or ferrimagnetic. This talk will
introduce the principles for designing these clusters and discuss a concept
where clusters can be viewed as super-atoms - adding a third dimension to
the periodic table. Recent experimental evidence to support this idea will
be presented. Examples of cluster assembled materials will include
high-energetic materials involving Al(MnO4)3, alkali metal clusters
isolated in zeolites, transition metal clusters supported on organic and
metallic substrates, and manganese-oxide clusters passivated by acetate
ligands. Ultimately the properties of crystals composed of clusters as the
building blocks will be discussed. It is hoped that the synergy between
theory and experiment will lead to the synthesis of cluster assembled
materials with unique and tailored properties, thus creating new
opportunities in materials science at the dawn of the new millennium.
|
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Friday, April 26, 2002
|
|
Sidney A. Coon
[Host: S. Liuti]
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|
4:00 PM, Room 204
|
|
NSF and New Mexico State University |
| Physics Building |
|
“A Singular Potential:from Theorist's Toy to Experimental Realization” |
ABSTRACT:
| The inverse square potential (V(r)~1/r**2), first studied by Cote,
a contemporary of Isaac Newton, is an interesting potential for
nonrelativistic quantum mechanics. It lies on the edge of the line
dividing potentials which can be treated in the familiar manner and those
which are singular. Singular potentials have been studied for a long time
because they can be regarded as models for nonrenormalizable field
theories, and, more recently, as an element of the new paradigm of
effective field theory methods in nuclear physics. In this talk, I will
demonstrate the mathematics of the 1/r**2 potential, including the
anomalous (quantum mechanical) breaking of scale symmetry and a rigorous
treatment of absorption ("fall to the center"). Correct mathematics leads
to a quantum mechanical understanding of the formation of anions
(electrons bound by the dipole moment of a polar molecule) and of a very
recent dedicated experimental study of this potential in the context of
manipulation of cold atoms. |
|
Friday, April 19, 2002
|
|
Larry Cardman
[Host: T. Gallagher]
|
|
4:00 PM, Room 204
|
|
JLab |
| Physics Building |
|
“Building Nucleons and Nuclei from Quarks and Glue: Early Results from the Research Program at Jefferson Lab” |
|
Friday, April 12, 2002
|
|
Thomas Gallagher
[Host: Eugene Kolomeisky]
|
|
4:00 PM, Room 204
|
|
University of Virginia |
| Physics Building |
|
“Spontaneous evolution from a cold Rydberg gas to an ultra cold plasma” |
|
Friday, March 29, 2002
|
|
A. Marchionni
[Host: S. Conetti]
|
|
4:00 PM, Room 204
|
|
Fermi Lab |
| Physics Building |
|
“Long baseline neutrino oscillation experiments: why and how” |
ABSTRACT:
| The evidence for neutrino oscillations from the SuperKamiokande
experiment still leaves several open questions. The present program
of long baseline neutrino oscillation experiments will address these
issues. The ongoing K2K experiment and the future JHF facility in Japan,
the programs in preparation in the United States (MINOS) and in Europe
(CNGS) will be reviewed. MINOS (Main Injector Neutrino Oscillation Search)
will be operating at the beginning of 2005 over a baseline of 735 km from
FERMILAB (Illinois) to Soudan (Minnesota). Status and goals of the MINOS
experiment will be reported in detail. |
|
Friday, March 22, 2002
|
|
Dr. Bruce Van Dover
[Host: Joseph Poon]
|
|
4:00 PM, Room 204
|
|
Agere Systems , Murray Hill NJ |
| Physics Building |
|
“High-performance dielectric thin films for science and technology” |
ABSTRACT:
| Ultrahigh-density dynamic random acess memory, hyperscaled field-effect
transistors, and field-effect-induced superconductivity at 117 K in
fullerenes are examples where high-performance thin film dielectrics
play a pivotal role in science and technology. In the past, only a
small set of materials (SiO2, Al2O3, (Ba,Sr)TiO3, etc.) have been
considered for these structures. We have assessed a wide range of
dielectric systems using a high-throughput, composition-spread
approach. This has lead to the discovery and development of dielectrics
with extremely high performance, as well as the identification of
unexpected physics by careful investigation of systematic trends.
I will discuss the scientific and technological issues, our approach to
discovery, and the interesting materials and materials physics we have
uncovered. |
|
Friday, March 8, 2002
|
|
Julian Noble
[Host: E. Kolomeisky]
|
|
4:00 PM, Room 204
|
|
University of Virginia |
| Physics Building |
|
“Running Out of Time: Why Elephants Don't Gallop” |
ABSTRACT:
Newtonian physics implies that running is impossible for sufficiently large animals. There are two main factors that influence this:
1. An animal's strength/weight ratio decreases with size, hence a
sufficiently large animal will be liable to injury if it attempts
a gallop.
2. The time required for an animal to move its limbs increases with
size, but the time an animal can remain in the air (while running)
does not scale with linear dimension. Therefore there is some size
beyond which an animal has "run out of time" and cannot take advantage of a running gait.
These aspects of the biomechanics of locomotion bear on the interesting
questions of determining the speeds of extinct species, as well as how
varying gravity affects locomotion.
|
|
Friday, March 1, 2002
|
|
N.O. Lipari
[Host: V. Celli]
|
|
4:00 PM, Room 204
|
|
Lipari Int'l Consulting |
| Physics Building |
|
“Physicists and Industry in the 21st Century: Who, What, How” |
ABSTRACT:
| The on-going global economic transformations require that industries
strongly focus on innovation, time to market, quality and cost in the
introduction of new products. The trend in each industry is to focus on core
competencies and obtain the additional resources from external alliances and
partnerships with Universities and Government. "Coopetition" is emerging as
the most effective approach for technology transfer, i.e. the path from idea
to products. This requires a totally different and much more pervasive role
of the physicist. In addition to the scientific skills, the scientist needs
interdisciplinary and communication skills in order to successfully interact
in the industrial environment. Examples will be given. Specific suggestions
for the role of the university in forming the physicists with the proper
requirements for the modern industry will be discussed. |
|
Friday, February 22, 2002
|
|
Kareljan Schoutens
[Host: Paul Fendley]
|
|
4:00 PM, Room 204
|
|
University of Amsterdam |
| Physics Building |
|
“New States of Matter in the Quantum Hall and BEC Regimes ” |
|
Friday, February 15, 2002
|
|
Despina Louca
[Host: T. Gallagher]
|
|
4:00 PM, Room 204
|
|
University of Virginia |
| Physics Building |
|
“Lattice Effects and Jahn-Teller Fluctuations in Crystals” |
ABSTRACT:
| In many systems i.e. magnetoresistive and superconducting oxides, the atomic structure couples strongly to the electronic degrees of freedom. In CMR crystals, Jahn-Teller effects are strongly related to the metal-insulator transition, for instance. The manganites are one example where the JT distortions are static and are important ingredients to the polaron lattice formation. In cuprates, when static distortions are present it usually means superconductivity is killed, while dynamic effects prevailing in the SC phase are sometimes too fast to observe. (La/Sr)CoO3 serves as a prototype for studying the crossover from static to dynamic effects. With the pair density function analysis and inelastic S(Q,w) measurements, it was determined that dynamical JT fluctuations induce a distorted atomic structure. The S(Q,w) clearly shows the presence of localized phonon modes most likely due to JT excitations, while the local structure transforms to an unusually glassy state that is intermediate to the manganites and cuprates. |
|
Friday, February 8, 2002
|
|
Jun Ye
[Host: T. Gallagher]
|
|
4:00 PM, Room 204
|
|
JILA |
| Physics Building |
|
“Light: Time Meets Frequency” |
|
Friday, February 1, 2002
|
|
Michael Turner
[Host: Craig Dukes]
|
|
4:00 PM, Room 204
|
|
University of Chicago |
| Physics Building |
|
“Making Sense of the New Cosmology” |
ABSTRACT:
| Cosmology is in its most exciting period of discovery yet.
Over the past five years we have determined the basic features
of the Universe -- spatially flat; accelerating; composed
of 1/3rd a new form of matter, 2/3rds a new form of energy,
with some ordinary matter and neutrinos; and apparently born
from a burst of rapid expansion during which quantum noise
was stretched to astrophysical size seeding cosmic structure.
Now we have to make sense of this: What is the dark matter
particle? What is the nature of the dark energy? Why this
mixture? How did the matter -- antimatter asymmetry arise?
What is the underlying cause of inflation (if it
occurred)? If we succeed in making sense of our Universe,
this will truly be remembered as a Golden Age. |
|
Friday, January 25, 2002
|
|
Olivier Pfister
[Host: T. Gallagher]
|
|
4:00 PM, Room 204
|
|
University of Virginia |
| Physics Building |
|
“Quantum information with quantum fields: creation and entanglement of twin beams of light” |
ABSTRACT:
| The concept of quantum information can be seen as stemming from the fascinating idea of putting quantum mechanics to practical use as such, and not only as the theory behind, in particular, microscopic physics. Because of the latter, it is sometimes believed that experimental efforts in quantum information only involve exquisite control over nanoscale entities such as single atoms or single photons (see last week's colloquium for a beautiful illustration). This is not rigorously true, as qubits can also be implemented using exquisitely controlled macroscopic entities, such as optical fields of milliwatt power. In this talk, I will present our endeavor to create bright entangled light sources suitable for quantum teleportation and quantum error correction, as well as our contribution to the theoretical understanding of such problems. |
|
Friday, January 18, 2002
|
|
Daniel Gammon
[Host: O. Pfister]
|
|
4:00 PM, Room 204
|
|
Naval Research Lab. |
| Physics Building |
|
“Optically probing and controlling a single quantum dot” |
|
Friday, December 7, 2001
|
|
Swapan Chattopadhyay
[Host: Donal Day]
|
|
4:00 PM, Room 204
|
|
JLAB |
| Physics Building |
|
“New Dimensions in Probing the Structure and Function of Matter: Concepts, Techniques and Technologies” |
ABSTRACT:
| We will explore various concepts, techniques and
technologies for producing ultrashort pulses of electrons and photons of
all energies and colors from the femtosecond to the attosecond duration
and beyond for breakthrough research in physics, chemistry, life and
information sciences |
|
Friday, November 30, 2001
|
|
Andrew Hime
[Host: Craig Dukes]
|
|
4:00 PM, Room 204
|
|
Los Alamos |
| Physics Building |
|
“Results from the Sudbury Neutrino Observatory” |
ABSTRACT:
| The Sudbury Neutrino Observatory (SNO) is a heavy water, imaging Cerenkov
detector operating 6800 feet underground in the Creighton Nickel Mine in
Ontario, Canada. With its heavy water target, SNO has the unique
capability to detect and separate three distinct 8B solar neutrino
signals through the charged current (CC), neutral current (NC), and
elastic scattering (ES) channels. By comparing the solar neutrino flux
deduced from the CC interaction (sensitive only to electron neutrinos)
with that deduced from the NC or ES interactions (sensitive to all active
neutrino flavors), SNO can make a unique study of the solar neutrino
deficit and a model independent test for neutrino oscillations. Results
from the pure D2O phase of SNO will be presented along with their
implications for elementary particle physics, astrophysics, and
cosmology. |
|
Friday, November 16, 2001
|
|
Michael Duff
[Host: P. Q. Hung]
|
|
4:00 PM, Room 204
|
|
University of Michigan |
| Physics Building |
|
“A Layman's Guide To M-Theory” |
ABSTRACT:
| Superunification of the fundamental interactions underwent a major
paradigm shift in 1984 when eleven-dimensional supergravity was
knocked off its pedestal by ten-dimensional superstrings. 1995
witnessed another shift of equal proportions, however, when
superstrings were themselves superseded by ``M-theory'', a
non-perturbative theory which describes extended objects with two dimensions
(supermembranes) and five dimensions (superfivebranes), which subsumes all
five
consistent string theories and whose low-energy limit is, ironically,
eleven-dimensional supergravity. |
|
Friday, November 9, 2001
|
|
Mariano Quiros
[Host: P. Q. Hung]
|
|
4:00 PM, Room 204
|
|
Istituto de Estructura de la Materia (CSIC), Madrid, Spain |
| Physics Building |
|
“The Long Way From Strings To Large Extra Dimensions ” |
ABSTRACT:
| In the first part of the talk I will review the main ideas going from
string models to the possibility of low string scales and large extra
dimensions. In particular the subjects of bosonic and fermionic strings
(IIA, IIB, heterotic and type I/I'), T-duality and D-branes, will be
covered. In the second half of the talk I will describe the different
scales which can appear in the various string constructions and provide
the experimental constraints on transverse (gravitational) and
longitudinal (gauge) dimensions using gravitational and collider data. |
|
Friday, November 2, 2001
|
|
Chris Monroe
[Host: Robert Jones]
|
|
4:00 PM, Room 204
|
|
University of Michigan |
| Physics Building |
|
“Building a quantum computer atom by atom” |
ABSTRACT:
| A quantum computer can store and process quantum superpositions of numbers. This parallelism leads to an exponential speedup over conventional computers for certain algorithms. However, the prospects for constructing a quantum computer are highly speculative, owing to the extremely fragile nature of quantum superpositions. A quantum computer is nothing more than a smaller (and more humane) version of Schroedinger's Cat, and if one is ever built, it will strongly impact both computer science and fundamental quantum mechanics. A leading physical candidate for a quantum computer is a collection of individual trapped atoms, controlled and manipulated with optical fields. Experiments are reported in this context, including the demonstration of simple quantum logic gates and the controlled generation of entangled quantum states. The outlook for future quantum computing with atoms or alternative technologies will be discussed. |
The Llewellyn G. Hoxton Lecture
Please not time and place
|
Monday, October 29, 2001
|
|
Gerald 't Hooft
[Host: Department of Physics]
|
|
7:30 PM, Room 402
|
|
University of Utrecht |
| Chemistry Building |
|
“The Universe of the Elementary Particles” |
|
Friday, October 26, 2001
|
|
G. 't Hooft
[Host: P. K. Kabir]
|
|
4:00 PM, Room 204
|
|
University of Utrecht, Netherlands |
| Physics Building |
|
“How does God Play Dice?
(Speculations about Quantum Mechanics at the Planck scale)” |
ABSTRACT:
| Attempts to arrive at consistent theories combining
Quantum Mechanics with General Relativity not only require new
concepts of space, time and matter, such as the ideas that lead
to Superstring Theory, D-brane theory and M-theory, but they
may also require a reconsideration of what Quantum Mechanics
itself really is about. Although completely deterministic
scenarios appear to be ruled out by the Bell inequalities,
it is nevertheless worth-while to investigate a set-up where
we start with a deterministic theory and add to this the
notion of information loss. Although models proposed so-far all
show deficiencies of some sort which makes them unrealistic for
describing the real world, these models do show how chaotic
phenomena in a deterministic theory might be suspected to lie
at the basis of the quantum nature of our world. |
|
Friday, October 19, 2001
|
|
Michael Widom
[Host: Joe Poon]
|
|
4:00 PM, Room 204
|
|
Carnegie Mellon University |
| Physics Building |
|
“Entropy in the Solid State” |
ABSTRACT:
| Equilibrium states of matter balance the thermodynamic
tendency to minimize energy with the simultaneous need to maximize
their entropy. Depending on the temperature, different equilibrium
states may occur representing different tradeoffs between energy and
entropy, leading potentially to a multiplicity of solid state phases.
The phase diagram of a superalloy and of the element Pu illustrate the
importance of entropy residing in modes of atomic vibrations.
Additional examples will be given of quasicrystal- and glass-forming
alloys in which the entropy resides instead in novel discrete
configurational degrees of freedom. |
|
Friday, October 12, 2001
|
|
David F. Anderson
[Host: Craig Dukes]
|
|
4:00 PM, Room 204
|
|
Fermi National Accelerator Laboratory |
| Physics Building |
|
“Understanding Flight” |
ABSTRACT:
| Through the years the explanation of flight has become mired in
misconceptions that have become dogma. Wolfgang Langewiesche, the author
of "Stick and Rudder" (1944) got it right when he wrote: "Forget
Bernoulli's Theorem". A wing develops lift by diverting (from above) a
lot of air. This is the same way that a propeller produces thrust and a
helicopter produces lift. Newton's three laws and a phenomenon called the
Coanda effect explain most of it.
With an understanding of the real physics of flight, many things become
clear. Inverted flight, symmetric wings, and the flight of insects are
obvious. It is easy to understand the power curve, high-speed stalls, and
the effect of load and altitude on the power requirements for lift. The
contribution of wing aspect ratio on the efficiency of a wing, and the
true explanation of ground effect will also be discussed. |
|
Friday, October 5, 2001
|
|
Arthur S. Brill
[Host: E. Kolomeisky]
|
|
4:00 PM, Room 204
|
|
University of Virginia |
| Physics Building |
|
“Hyperfine physics - from the hydrogen atom to hemoglobin” |
ABSTRACT:
| Hyperfine physics deals with interactions between electron and nuclear spins. Measurements of these interactions provide information about the electronic structure of paramagnetic sites in molecules and crystals. Examples will be presented and briefly discussed of the roles of such measurements in atomic, biological, condensed matter molecular and nuclear physics. |
|
Friday, September 28, 2001
|
|
Krishna Rajagopal
[Host: Peter Arnold]
|
|
4:00 PM, Room 204
|
|
MIT |
| Physics Building |
|
“From the QCD Phase Diagram to Heavy Ion Collisions and Back” |
ABSTRACT:
| I describe some of the things we think we know about the
physics of a hot quark-gluon plasma and the phase transition
between the stuff of the big bang and ordinary hadronic matter.
The questions I will pose motivate people
to collide heavy ions at relativistic energies.
I will give two examples of how we may use measurements made
in these experiments to map the QCD phase diagram,
and hence to study the condensed matter physics of QCD. |
|
Friday, September 21, 2001
|
|
Jun Ye
[Host: Thomas Gallagher]
|
|
4:00 PM, Room 204
|
|
JILA |
| Physics Building |
|
“Light: Time meets frequency” |
|
Friday, September 14, 2001
|
|
Puru Jena
[Host: Lou Bloomfield and Joe Poon]
|
|
4:00 PM, Room 204
|
|
Virginia Commonwealth University , Richmond, VA - Department of Physics |
| Physics Building |
|
“TheRole of Clusters in the Design of Nano-Scale Systems” |
ABSTRACT:
| Atomic clusters consisting of a few to a few thousand atoms constitute a
new phase of matter intermediate between atoms and solids. Unlike
conventional nanostructured materials, the size and composition of these
clusters can be controlled one atom at a time. The properties of such
clusters brought about by their large surface-to-volume ratio, unique
geometry, low dimensionality and reduced coordination, exhibit novel
behavior quite unlike that in the bulk. For example, metallic elements can
be made to form ionic bonds while nonmagnetic and anti-ferromagnetic
materials can become ferromagnetic or ferrimagnetic. This talk will
introduce the principles for designing these clusters and discuss a concept
where clusters can be viewed as super-atoms - adding a third dimension to
the periodic table. Recent experimental evidence to support this idea will
be presented. Examples of cluster assembled materials will include
high-energetic materials involving Al(MnO4)3, alkali metal clusters
isolated in zeolites, transition metal clusters supported on organic and
metallic substrates, and manganese-oxide clusters passivated by acetate
ligands. Ultimately the properties of crystals composed of clusters as the
building blocks will be discussed. It is hoped that the synergy between
theory and experiment will lead to the synthesis of cluster assembled
materials with unique and tailored properties, thus creating new
opportunities in materials science at the dawn of the new millennium. |
|
Friday, September 7, 2001
|
|
J. Elkins
[Host: T. Gallagher]
|
|
4:00 PM, Room 204
|
|
National Oceanic and Atmospheric Administration |
| Physics Building |
|
“A Problem in Atmospheric physics: Stratospheric ozone depletion” |
ABSTRACT:
| Since 1987, almost all countries have signed the Montreal Protocol to control substances that cause depletion of the ozone layer. One of the successes of the Protocol has been the dramatic decrease in emissions of methyl chloroform, a metal degreaser that has been responsible for the decline of total equivalent chlorine in the atmosphere. However, chlorofluorocarbon (CFC-12), a common refrigerant, and the halons, fast-acting fire extinguishing agents, are still increasing in the atmosphere even though production ceased for the developed countries in 1996. This research talk will discuss ground-based and airborne measurements and their implication for the future ozone depletion. Preliminary results from a recent field campaign operated on the Trans-Siberian Railway will also be presented. |
Special Colloquium-Please note special time
|
Friday, May 11, 2001
|
|
Professor James Stone
[Host: Robert Jones]
|
|
11:00 AM, Room 204
|
|
Boston University and Department of Energy |
| Physics Building |
|
“A Study of Atmospheric Neutrinos with the Super-Kamiokande Detector” |
ABSTRACT:
| The observation of flavor oscillations in atmospherically produced neutrinos by the Super-Kamiokande Experiment represents the first indication of massive neutrinos and new physics beyond the Standard Model of Particle Physics. Neutrino physics in the context of oscillations will be discussed and a detailed description of the Super-Kamiokande detector will be presented. The latest experimental results on proton decay, atmospheric and long baseline neutrino studies will be shown. |
|
Friday, May 4, 2001
|
|
Dr. Jeff Appel
[Host: Brad Cox]
|
|
4:00 PM, Room 204
|
|
Fermilab |
| Physics Building |
|
“The Fixed-Target Charmed Road to Understanding Hadrons” |
ABSTRACT:
| Measurements involving charm quarks tell us about the nature and details of light hadrons. This talk will summarize how and what we are learning from charm fixed-target experiments about the usual ground-state hadrons, and about scalar resonances such as the sigma, kappa, and f_0's which have had uncertain histories so far. |
Special Colloquium
|
Thursday, May 3, 2001
|
|
Pierre Pillet
[Host: Thomas Gallagher]
|
|
4:00 PM, Room 204
|
|
Laboratoire Aime Cotton |
| Physics Building |
|
“Formation and Trapping of Ultracold Molecules by Photoassociation” |
|
Friday, April 27, 2001
|
|
Brian Cole
[Host: C. Dukes]
|
|
4:00 PM, Room 204
|
|
Columbia University |
| Physics Building |
|
“The Baryon Junction and High-Energy Nuclear Collisions” |
ABSTRACT:
| In the 1970's Veneziano suggested the existence of a set of diagrams in
Regge theory that could allow the baryon number to be "extracted" from
a baryon in a single step in high-energy hadronic interactions. Because
no experimental evidence for these diagrams was found, the idea was
largely forgotten. However, in recent years it has been resurrected and
re-cast in terms of the so-called "baryon junction" a (possible)
non-perturbative topological defect in the gluon fields within the
baryon. In this picture, the junction plays the role of "bookkeeper"
for baryon number conservation in high-energy collisions. Current
theoretical models suggest that diagrams involving the exchange of the
junction only become important in hadronic (e.g. p-p) collisions at
collider energies. However, the junction may become active at much
lower energies in nuclear collisions due to the multiple interaction of
the incident nucleons. I will use results from a new generation of
experiments studying proton-collisions at the Brookhaven National
Laboratory AGS and CERN SPS accelerators to illustrate the possible role
played by the junction in the "stopping" of the protons and in the
abundant production of strange baryons and the production of
anti-baryons. I will then discuss the possibility that the junction may
be responsible for some of the anomolous results obtained from
fixed-target heavy-ion experiments at the CERN SPS that were recently
argued to provide evidence for quark-gluon plasma formation in
high-energy nuclear collisions. I will discuss future studies of
junction physics in fixed-target proton-nucleus experiments and in
proton-proton and proton-nucleus collisions at the Relativistic Heavy
Ion Collider. I will finish by highlighting some recent speculation
that novel states of matter formed from "meshes" of junctions and
anti-junctions may be created in heavy-ion collisions at RHIC. |
|
Friday, April 20, 2001
|
|
Hank Thacker
[Host: Joseph Poon]
|
|
4:00 PM, Room 204
|
|
University of Virginia |
| Physics Building |
|
“How QCD Works” |
ABSTRACT:
| Mathematically, the interaction between quarks and gluons is
remarkably similar to the electromagnetic interaction of electrons
and photons. But unlike QED, QCD has an essentially nonperturbative
structure, as exhibited most strikingly by the absolute confinement
of quarks, which represents a fundamental property of the QCD vacuum
(complete screening of color charge). Another property of QCD, chiral
symmetry breaking, is also a statement about the vacuum, i.e. that it is
full of quark-antiquark pairs (analogous to Cooper pairs in BCS theory).
Chiral symmetry breaking and quark confinement are probably related
phenomena, but the connection is poorly understood. I will discuss
recent lattice calculations which have begun to expose the structure
of the QCD vacuum. |
|
Friday, March 30, 2001
|
|
Professor Hongxing Jiang
[Host: E. Kolomeisky and J. Poon]
|
|
4:00 PM, Room 204
|
|
Kansas State |
| Physics Building |
|
“III-Nitride Micro- and Nano-Structures and Devices” |
ABSTRACT:
| Advances in materials research and novel structure designs have brought the dimensions of photonic devices to the scales of the wavelength of the light they emit, transmit, and detect. In this realm, quantum nature of light dominates, enabling more efficient and fast devices. In this talk, the fabrication and optical studies of micron and wavelength-scale photonic structures, including micro-cavities and micro-size light emitters, based on III-nitride wide bandgap semiconductors will be presented. Our recent work on sub-micron photonic structures prepared by e-beam lithography and plasma etching will be discussed. Potential applications of III-nitride micro- and nano-photonics in efficient energy conversion and optical communications will be also be summarized. |
|
Friday, March 23, 2001
|
|
William Wootters
[Host: Olivier Pfister]
|
|
4:00 PM, Room 204
|
|
Williams College |
| Physics Building |
|
“Quantum Entanglement as a Resource for Communication” |
ABSTRACT:
| Quantum mechanical objects can exhibit correlations with one another
that
are fundamentally at odds with the paradigm of classical physics; one
says
that the objects are "entangled." In the past few years, entanglement
has
come to be studied not only as a marvel of nature but also as a
potential
resource, particularly as a resource for certain unusual kinds of
communication. This talk reviews three proposed communication schemes
based on entanglement: (i) dense coding, which is the effective doubling
of
the information-carrying capacity of a quantum particle through prior
entanglement with a particle at the receiving end; (ii) teleportation,
in
which a quantum state is transferred from one particle to another over a
distance, apparently without traversing the intervening space; and (iii)
the efficient pooling of classical data, in which separated participants
arrive at a conclusion faster because they share entanglement. These
three
schemes highlight three distinct ways in which entanglement can enhance
communication. |
|
Friday, March 9, 2001
|
|
Evelyn Patterson
[Host: Steve Thornton]
|
|
4:00 PM, Room 204
|
|
U. S. Air Force Academy |
| Physics Building |
|
“Using the World Wide Web for Physics Teaching and Learning: Exploring Where Pedagogy and Technology Meet” |
ABSTRACT:
| The explosion of World Wide Web technology over the past several
years has spurred the development of an ever-increasing number of web-based
teaching and learning materials and techniques. Web technology is being used
to support student-teacher, student-student, and teacher-teacher
communications, often providing communications channels and possibilities
not possible previously. At the same time, physics education research
continues to provide more insight about how, why, and the extent to which
our students do-- and don't-- learn physics. Can our research-based
understanding of how students learn and the new unprecedented power of
communications lead us to improved courses and programs? This talk will
survey the spectrum of ways in which the web is being used by the physics
education community to promote physics teaching and learning. It will also
introduce and discuss a unique mix of pedagogy and the web technology, the
"Just-in-Time Teaching" (JiTT) strategy, now being implemented by over 120
faculty at more than 60 institutions across the country and in Canada and
Europe." |
|
Friday, March 2, 2001
|
|
B. Lee Roberts
[Host: Blaine Norum]
|
|
4:00 PM, Room 204
|
|
Boston University |
| Physics Building |
|
“Recent news from the vacuum? The Muon g-2 Experiment at Brookhaven” |
ABSTRACT:
| Since the experiments of Stern and Gerlach, magnetic moments of "elementary" particles have been important in our quest to understand subatomic physics. A brief review of the history and foundations of this field will be given as an introduction to the muon g-2 experiment at the Brookhaven AGS. This experiment, E821, has recently reported a new result with a relative accuracy of 1.3 ppm, which is larger than the theoretical (Standard Model) value by 2.6 standard deviations. The physics context of this measurement, the experiment, and the analysis leading to this new result will be presented. |
|
Friday, February 23, 2001
|
|
Jamie Nagle
[Host: Simonetta Liuti]
|
|
4:00 PM, Room 204
|
|
Columbia University |
| Physics Building |
|
“First results from the Relativistic Heavy Ion Collider” |
|
Friday, February 16, 2001
|
|
Prof. Pulak Dutta
[Host: Joseph Poon]
|
|
4:00 PM, Room 204
|
|
Northwestern Univ. |
| Physics Building |
|
“Nanoscale ordering in soft materials near surfaces and interfaces” |
ABSTRACT:
| A material is 'soft' if its structure, and thus its properties, can change in response to very weak stimuli; hence the current interest in using soft materials for switching, sensing, etc. One way to induce structures that do not occur otherwise is with the help of a surface or interface. This talk will give some examples of the use of synchrotron radiation to look at how molecules self-organize near surfaces and soft-hard interfaces. Our studies of Langmuir monolayers (including their use as templates for inorganic nucleation), self-assembled films, and normal liquids near interfaces will be described. |
|
Friday, February 9, 2001
|
|
Nilanga Liyanage
[Host: Gordon Cates]
|
|
4:00 PM, Room 204
|
|
Jefferson Laboratory |
| Physics Building |
|
“Neutron Spin Structure Function Measurements at Jefferson Lab” |
ABSTRACT:
| Spin structure functions provide basic information about the spin of the quark
distributions inside the nucleon. Measurements at high energy
laboratories have
provided precision spin structure function data at low values of xbj.
However, there
is little precision data at low and moderate values of momentum transfer
and high
values of xbj . This is especially true for the neutron due to the
absence of a free
neutron target. Polarized ND3 , NH3 and 3He targets at Jefferson lab combined
with its high-polarization continuous electron beam have provided the opportunity
to make high precision neutron spin structure measurements in the high
xbj region.
As examples of high precision measurements possible at Jefferson lab, I
will describe
two planned neutron spin structure measurements, one in the deep
inelastic region
and the other in the resonance region, using the Hall A polarized 3He
target. The
deep inelastic measurement will provide the first precision test of
predictions for the
virtual photon asymmetry An1 in the valence quark region. The
measurement in the
resonance region, combined with the DIS measurement will provide a first
test of
quark-hadron duality for spin structure of the neutron |
|
Thursday, February 8, 2001
|
|
Jun Ye
[Host: T. Gallagher]
|
|
4:00 PM, Room 204
|
|
JILA |
| Physics Building |
|
“TBA” |
Joint Physics/Biology Colloquium
|
Friday, January 19, 2001
|
|
Alan McKane
[Host: Tim Newman]
|
|
4:00 PM, Room 204
|
|
Department of Physics -University of Manchester, UK |
| Physics Building |
|
“Ecological dynamics of multispecies communities” |
ABSTRACT:
| Many theoretical physicists with a background in non-equilibrium statistical
mechanics are becoming interested in exploring mathematical models of
ecosystems. The reason for this is clear when one realizes that such models
typically involve a large number of individuals interacting according to
simple rules and that the ultimate aim is to compute coarse-grained or
long-time behavior. The ingredients of these models include population
dynamics, predator-prey interactions, competitive effects, speciation
and immigration. Two examples will be discussed. One is a model which
describes the evolution of food webs using adaptive dynamics and the other,
a stochastic model of species-rich ecosystems which makes predictions
concerning the form of the species abundance distribution. |
|
Friday, December 8, 2000
|
|
Prof. A T. Johnson, Jr.
[Host: Joseph Poon]
|
|
4:00 PM, Room 204
|
|
Univ. of Pennsylvania |
| Physics Building |
|
“Quantum Confinement of Electrons and Phonons in Single Wall Carbon Nanotubes” |
ABSTRACT:
| Single wall carbon nanotubes are a fascinating set of nanomaterials whose unique physical properties reflect the effect of quantum confinement on the electronic and phonon energy spectrum. Electron waves confined to the cylindrical tube wall obey periodic boundary conditions. Their energy spectrum consists of a set of one-dimentional subbands, making nanotubes metals or semiconductors depending on the precise wrapping of the constituent graphene sheet. I will discuss functional nanotube devices we have made, including field effect transistors, diodes, and highly conducting electrical interconnects. Nanotube sound waves (phonons) also experience quantum size effects. This makes nanotubes incredibly stiff, and may enable mechanical composites or nano-mechanical systems. We recently measured the effect of the quantized phonon spectrum on the specific heat of nanotubes as well as their thermal conductivity. Our results support theoretical predictions that nanotubes have an extremely high thermal conductivity, perhaps the highest of any known material. |
|
Friday, November 10, 2000
|
|
Rick Trebino
[Host: Louis Bloomfield]
|
|
4:00 PM, Room 204
|
|
Georgia Tech |
| Physics Building |
|
“The Musical Score, the Fundamental Theorem of Algebra, and the Measurement” |
ABSTRACT:
| To measure an event in time requires a shorter one. As a result, the
development of a technique to measure ultrashort laser pulses--less than
10-12 seconds long and the shortest events ever created--has been
particularly difficult. We have, however, recently developed a simple
method for fully characterizing these events, that is, for measuring a
pulse's intensity and phase vs. time. This method relies on two seemingly
unrelated ideas: the concept of the musical score and the fact that the
Fundamental Theorem of Algebra fails in two dimensions. Specifically, an
optical analog of a musical score of the pulse is produced by measuring its
spectrogram. And the mathematics involved is equivalent to the
two-dimensional phase-retrieval problem--a problem that is solvable only
because the Fundamental Theorem of Algebra fails in two dimensions. We call
the method Frequency-Resolved Optical Gating (FROG), and it is simple,
rigorous, intuitive, and general. It can measure pulses in all spectral
ranges, on a single-shot basis, and over a wide range of energies. FROG has
been used to measure pulses as short as 4.5 femtoseconds (4.5 x 10-15 sec),
and it can measure two pulses simultaneously. More recently, we have shown
that FROG can be used in conjunction with spectral interferometry to measure
essentially arbitrary pulses with as little as zeptojoules of energy (less
than one photon!) on a multi-shot basis.
|
|
Friday, November 3, 2000
|
|
Margaret Murray
[Host: Simonetta Liuti]
|
|
4:00 PM, Room 204
|
|
Department of Mathematics, Virginia Tech |
| Physics Building |
|
“Women Becoming Mathematicians: The Doctoral Classes of 1940-1959” |
ABSTRACT:
| I give a report on an oral history-based study of the approximately 200
women who earned Ph.D.'s in mathematics from American colleges and
universities during the years 1940-1959. I focus in some detail on the
following questions: How did the women of this generation develop their
mathematical interests and ambitions? Which individuals and institutions
were particularly supportive of their mathematical goals? What obstacles
to professional success did they encounter as they tried to build careers
in mathematics? How did they balance the competing demands of career and
personal life? How did they strike a balance between teaching, research,
and service to the profession? What lessons can contemporary
mathematicians, male and female, learn from the experiences of this
generation? |
Special Atomic Colloquium -
Please note special time
|
Wednesday, November 1, 2000
|
|
Yanhua Shih
[Host: O. Pfister]
|
|
4:00 PM, Room 204
|
|
Univ. of Maryland Baltimore County |
| Physics Building |
|
“Quantum Entanglement and Quantum Teleportation” |
|
Friday, October 27, 2000
|
|
Boris Kayser
[Host: P.Q. Hung]
|
|
4:00 PM, Room 204
|
|
National Science Foundation |
| Physics Building |
|
“ Why do We Think Neutrinos Have Mass? And What's Next? ” |
ABSTRACT:
| We explain why the evidence for nonzero neutrino masses is
compelling. Then, we turn to the questions about neutrinos raised by the
presence of their nonzero masses. These questions include: How many
different neutrinos are there? How much do they weigh? Is each neutrino
identical to its antiparticle? How will we answer questions like these?
|
|
Friday, October 20, 2000
|
|
Joe Thompson
[Host: Shivaram]
|
|
4:00 PM, Room 204
|
|
LANL |
| Physics Building |
|
“Superconductivity in a New Family of Heavy-Fermion Compounds” |
ABSTRACT:
| The discovery of superconductivity in CeCu2Si2
nearly 20 years ago was totally unexpected and contradicted
fundamental tenants of the well-established BCS theory of
superconductivity. Instead of the magnetic moment carried
by Ce+3 suppressing superconductivity, as expected from
BCS, the presence of Ce was essential for superconductivity
and responsible for increasing the effective mass of the
electrons participating in superconductivity by
orders-of-magnitude-hence, heavy-fermion superconductivity.
As we now know, CeCu2Si2 was the first example of
superconductivity mediated by antiferromagnetic spin
fluctuations, which also may be the dominant pairing
mechanism in high-temperature superconductors, and other
parallels between heavy-fermion and cuprate
superconductivity are emerging. Recently, we have
discovered a new family of heavy-fermion materials, CeMInsub5
(M=Rh, Co, and Ir), in which superconductivity appears at
temperatures higher than in any other heavy-fermion system.
These materials form in a quasi-2D structure, which makes
an analogy with the cuprate's magnetism and
superconductivity appealing. Though much remains to be
learned about their properties, this new family appears to
be quite interesting and provocative. |
|
Friday, October 6, 2000
|
|
Professor Marvin Girardeau
[Host: Eugene Kolomeisky]
|
|
4:00 PM, Room 204
|
|
University of Arizona |
| Physics Building |
|
“Theory of de Broglie Waveguides” |
ABSTRACT:
| Several experimental groups have recently succeeded in constructing
quasi-one-dimensional (1D) atom waveguides and loading them with
Bose-Einstein condensates of ultracold atomic vapors. An important
motivation for such studies is the goal of constructing atomic de Broglie
wave beam splitters and interferometers for ultrasensitive detection
of very weak accelerations and gravitational perturbations. This talk
will discuss the many-body Schrodinger dynamics of 1D systems of
impenetrable bosons, which is exactly soluble via an exact mapping from
an ideal Fermi gas to a strongly interacting Bose gas of impenetrable
point particles. After description of some completed work
on such systems in 1D toroidal geometries and harmonic traps,
some work in progress will be described, concerned with a generalization
to a model of a de Broglie beam splitter/interferometer using two
coupled waveguides.
|
Joint Astronomy-Physics Colloquium
|
Monday, October 2, 2000
|
|
Max Tegmark
[Host: T. X. Thuan]
|
|
4:00 PM, Room 201
|
|
University of Pennsylvania - Physics Dept. |
| Astronomy Building |
|
“Zeroing in on cosmological parameters” |
ABSTRACT:
| I describe the sharp constraints on cosmological paramaters placed by recent measurements of the cosmic microwave background, distant supernovae, galaxy clustering, etc., and how different types of measurements how allow powerful cross-checks to be made. I also comment on outstanding puzzles in the emerging cosmological "standard model" and upcoming measurements that may resolve them. |
|
Friday, September 29, 2000
|
|
Richard Hughes
[Host: Simonetta Liuti]
|
|
4:00 PM, Room 204
|
|
Los Alamos National Laboratories |
| Physics Building |
|
“Quantum cryptography” |
ABSTRACT:
| Quantum cryptography, or more accurately quantum key distribution (QKD),
uses single-photon transmissions to generate the shared, secret random
number sequences, known as cryptographic keys, which are used to encrypt
secret communications. Appealing features of QKD are that its security is
based on principles of quantum physics and attempted eavesdropping can be
detected. (Heisenberg’s uncertainty principle ensures that an adversary can
neither successfully tap the key transmissions, nor evade detection because
eavesdropping raises the key error rate above a threshold value). I shall
describe two quantum cryptography systems, based on the transmission of
non-orthogonal single-photon states to generate shared key material, at Los
Alamos. In one experiment we are generating key material over a 48-kilometer
optical fiber path, and in the other by transmitting photons over a 1.6-km
atmospheric path in daylight. In both cases, key material is built up using
the transmission of a single-photon per bit of an initial secret random
sequence. A quantum-mechanically random subset of this sequence is
identified, becoming the key material after a data reconciliation stage with
the sender. The atmospheric results show that QKD could be used for surface
to satellite transmissions. |
|
Friday, September 22, 2000
|
|
Laszlo Tisza
[Host: Vittorio Celli]
|
|
4:00 PM, Room 204
|
|
MIT |
| Physics Building |
|
“History of the two-fluid model and Bose-Einstein condensation” |
|
Friday, September 15, 2000
|
|
Professor Subir Sachdev
[Host: Eugene Kolomeisky]
|
|
4:00 PM, Room 204
|
|
Yale University |
| Physics Building |
|
“ Quantum criticality in the high temperature superconductors” |
ABSTRACT:
| I discuss the phases and critical points of quantum antiferromagnets in two dimensions
and their relationship to the physical properties of the high temperature superconductors. Non-magnetic impurities are argued to be
a sensitive probe of the wavefunction of the electron spins: I will describe
recent experiments on such impurities and the theoretical insights they
have provided on the interplay of antiferromagnetism and superconductivity.
|
Joint Chemistry/Physics Colloquium
|
Friday, September 1, 2000
|
|
Shaul Mukamel
[Host: Ian Harrison]
|
|
4:00 PM, Room 304
|
|
University of Rochester - Chemistry Dept. |
| Chemistry Building |
|
“Collective excitations and Multidimensional optical spectroscopies of dendrimers and biomolecules” |
Joint Physics and Engineering Physics Colloquium
|
Friday, April 28, 2000
|
|
Joel Fajans
[Host: J. Dorning/Joseph Poon]
|
|
4:00 PM, Room 204
|
|
University of California at Berkely |
| Physics Building |
|
“Pure-Electron Plasma Experiments” |
ABSTRACT:
Plasmas made only of electrons are remarkably stable and manipulatable. They are ideal for studying basic plasma physics, two-dimensional fluid dynamics, and nonlinear dynamics. I will discuss some basic plasma results, including a demonstration that like charges can attract rather than repel, and that sometimes mountaintops are just as stable as valley floors. Next I will describe some fluid results like the instability shown in the figure below. Finally I will discuss autoresonance, a very basic and general phenomenon which occurs in nonlinear oscillator systems.
|
|
Friday, April 14, 2000
|
|
Eugene Kolomeisky
[Host: Joseph Poon]
|
|
4:00 PM, Room 204
|
|
University of Virginia |
| Physics Building |
|
“Superfluidity in low dimensions: beyond the mean-field theory” |
ABSTRACT:
| The Gross-Pitaevskii approximation is a long-wavelength theory widely used
to describe a variety of properties of dilute Bose condensates, in
particular trapped alkali gases. In this talk I will show that for
short-ranged repulsive interactions this theory fails in one and two spatial
dimensions, and appropriate low-dimensional modifications will be proposed.
The new theory has a universal character, and some of its implications such
as density profiles in confining potentials, superfluidity, solitons, and
self-similar solutions will be discussed. |
|
Friday, March 31, 2000
|
|
E. Fischbach
[Host: Rogers Ritter]
|
|
4:00 PM, Room 204
|
|
Purdue University |
| Physics Building |
|
“The Search for Non-Newtonian Gravity” |
ABSTRACT:
| Ongoing attempts to unify the known fundamental forces lead to the
suggestion that there may exist new gravity-like forces in nature. These
would arise from the exchange of new light bosonic quanta among the
constituents of ordinary matter, and would produce apparent deviations from
the predictions of Newtonian gravity. The suggestion of such a "fifth force"
in 1986 has led to a broadened view of the interaction of gravity and other
known and hypothetical forces, and has helped to stimulate a large number of
new experiments to search for weak long-range forces. This talk will review
both the theoretical motivation for such new forces, and the experimental
results that have been obtained to date.
More recently newer string-inspired theories have suggested the presence of
additional macroscopic forces acting over sub-millimeter distances. Detecting
such forces presents special challenges-both theoretical and experimental-
for reasons that I will discuss. |
SPECIAL COLLOQUIUM
|
Friday, March 24, 2000
|
|
Yongsheng Gao
[Host: Brad Cox]
|
|
4:00 PM, Room 204
|
|
Harvard University |
| Physics Building |
|
“On the road to measure CP violation and test the Standard Model:Observation of hadronic b --> u transitions” |
ABSTRACT:
| CP violation is one of the great mystery of the universe.
The major motivation of the first-generation B factories is to measure
CP violations in the B meson system, especially the three CKM angles
Alpha, Beta and Gamma. I'll present the first observation of hadronic
b --> u transitions (B --> Pi+Rho-, Pi+Rho0, Pi+Pi-) which will be very
important for the future measurements of the CKM angles Alpha and Gamma.
Measuring Alpha and Gamma using these decay modes at the first-generation
B factories will be discussed, along with a future outlook of B physics |
|
Friday, March 17, 2000
|
|
Prof. Gerassimos (Makis) Petratos
[Host: Oscar Rondon]
|
|
4:00 PM, Room 204
|
|
Kent State University |
| Physics Building |
|
“Elastic Electron Deuteron Scattering: Past, Present and Future” |
ABSTRACT:
| This talk will present a review of elastic electron scattering
off the simplest nucleus, the deuteron. The elastic
scattering process has long been a crucial tool in understanding
the internal structure and dynamics of the nuclear two-body
system. Studies of the deuteron form factors, measured in
elastic scattering, offer unique opportunities to test both the conventional meson-nucleon "standard model" that describes the
deuteron electromagnetic structure, and "nuclear chromodynamics"
predictions of perturbative Quantum Chromodynamics based on the
underlying quark-gluon substructure of the deuteron.
A review of both the theoretical framework and of past (SLAC) and recent
(JLab) measurements of the deuteron form factors will be presented
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Friday, March 10, 2000
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Eric Zimmerman
[Host: Brad Cox]
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4:00 PM, Room 204
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Columbia University |
| Physics Building |
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“Searching for new particles in a high-energy neutrino beam: New results from Fermilab” |
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Friday, March 3, 2000
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Roger Chevalier
[Host: P. Q. Hung]
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4:00 PM, Room 204
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University of Virginia |
| Physics Building |
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“Supernova - Gamma Ray Burst Connection” |
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Friday, February 25, 2000
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Takeshi Egami
[Host: Despina Louca]
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4:00 PM, Room 204
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University of Pennsylvania |
| Physics Building |
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“Dealing with Regional Conflict: Spin-Charge Inhomogeneity in Superconducting Cuprates and CMR Manganites.” |
ABSTRACT:
| The discovery of high-temperature superconductivity was a double shock to the condensed matter physics community. Not only the critical temperature was so outrageously high (until then 30 K was considered to be the theoretical maximum), but magnetism appeared to be intimately involved, while for a long time magnetism had been considered to be incompatible with superconductivity. It then became the holy grail of theoreticians to overcome this apparent paradox, and various high-wire-act theories have been proposed. In the meantime, experimental data are accumulating that suggest a more conventional method of avoiding regional conflict between the spin and charge, by segregation. However, just as the social and international problems complete segregation simply defers the problem and does not solve it. Oxides are far ahead of us, and appear to have reached an intelligent solution. We discuss the results of recent inelastic and elastic neutron scattering measurements on cuprates and manganites, and speculate what this solution might be. |
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Friday, February 18, 2000
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Paul Fendley
[Host: Joseph Poon]
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4:00 PM, Room 204
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Univerisy of Virginia - Physics |
| Physics Building |
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“The Observation of Fractional Charge” |
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Friday, February 4, 2000
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Eugene Kolomeisky
[Host: Joseph Poon]
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4:00 PM, Room 204
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University of Virginia |
| Physics Building |
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“Breaking a one-dimensional chain: fracture in 1 + 1 dimensions” |
ABSTRACT:
| The breaking rate of an atomic chain stretched at zero temperature by a
constant force can be calculated in a quasiclassical approximation by
finding the localized solutions ("bounces") of the equations of classical
dynamics in imaginary time. We show that this theory is related to the
critical cracks of stressed solids, because the world lines of the atoms in
the chain form a two-dimensional crystal, and the bounce is a crack
configuration in (unstable) mechanical equilibrium. Thus the tunneling
time, Action, and the breaking rate in the limit of small forces are
determined by the classical results of Griffith. For the limit of large
forces we give an exact bounce solution that describes the quantum fracture
and classical crack close to the limit of mechanical stability. This limit
can be viewed as a critical phenomenon for which we establish a
Levanyuk-Ginzburg criterion of weakness of fluctuations, and propose a
scaling argument for the critical regime. The post-tunneling dynamics is
understood by the analytic continuation of the bounce solutions to real time. |
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Friday, January 28, 2000
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Robert Hull
[Host: Joseph Poon]
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4:00 PM, Room 204
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Dept. Materials Science and Engineering, UVA |
| Physics Building |
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“New Techniques For Nanoscale Fabrication And Characterization” |
ABSTRACT:
| The gallium focused ion beam produces highly collimated (10 nm - 1(mu)m) beams of high energy (3 - 30 kV) ions. These beams may be used as nanoscale “scalpels” to micromachine virtually any material by direct sputtering of the target surface. Combined with ion-beam induced deposition from organic vapors, this provides unique capabilities for sub 100 nm fabrication of three dimensional structures. I will describe how these capabilities form the basis of a new “nanoprinting” technology, for deep sub-micron pattern definition over planar and curved surfaces.
In addition, imaging and spectroscopy in the focused ion beam system enables new routes for three-dimensional characterization and visualization of microscale structures. During sputtering by the primary beam, large numbers of secondary electrons and ions are produced, which may be used to form images of the sputtered surface. By concatenating images of surfaces at different depths during the sputtering process, three-dimensional reconstructions of the structure may be generated. These reconstructions can contain up to 107 independent pixels of information. Furthermore, using a quadrupole mass spectrometer, element-specific images may be obtained. These techniques enable “miroscopy in the third dimension” which can be of immediate and powerful impact in understanding material microstructure.
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Friday, December 3, 1999
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Prof. Sid Redner
[Host: E. Kolomeisky]
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4:00 PM, Room 204
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Boston University |
| Physics Building |
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“Aggregation Kinetics in Gelation, Traffic, Wealth, and other Everyday Phenomena” |
ABSTRACT:
| In aggregation, clusters meet and irreversibly merge so that their
average size grows continuously with time. This process describes, for
example, making of jello and yogurt, raindrop formation in clouds, and the
mass distribution of stars. I will present an elementary overview of cluster
evolution in such aggregating systems. I begin by outlining the mean-field
theory of aggregation and showing how scaling provides basic insights into
long-time behavior. I will then discuss the intriguing relation between the
cluster-size distribution and the first-passage probability of a random walk.
Finally, I will discuss recent applications to traffic clustering and the
distribution of wealth. |
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Friday, November 19, 1999
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Jim Stone
[Host: Craig Dukes]
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4:00 PM, Room 204
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Boston University/Department of Energy |
| Physics Building |
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“Neutrino Mass--Experimental Results from Super-Kamiokande” |
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Friday, November 12, 1999
|
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Professor Ctirad Uher
[Host: Joseph Poon]
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4:00 PM, Room 204
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University of Michigan |
| Physics Building |
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“Materials with Open Structures as Novel Thermoelectrics” |
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Friday, November 5, 1999
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David Spergel
[Host: Peter Arnold]
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4:00 PM, Room 204
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Princeton University |
| Physics Building |
|
“Cosmic Microwave Background Fluctuations: A Probe of Cosmology” |
ABSTRACT:
| Observations of the microwave background are a powerful probe
of the physics of the early universe and of cosmological parameters.
Over the past few years, there has been a dramatic improvement in
the quality of data. The current observations are consistent
with a flat universe with a cosmological constant in which inflation
produced the primordial fluctuations.
Next year, NASA plans to launch MAP,
a satellite that will make precision measurements of
microwave background fluctuations. With these measurements,
we will be able to test our basic cosmological paradigm. If correct,
we can then use these observations to measure the basic cosmological
parameters to high precision. |
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Friday, October 29, 1999
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Alwyn Wootten
[Host: Bascom Deaver]
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4:00 PM, Room 204
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National Radio Astronomy Observatory |
| Physics Building |
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“The Atacama Large Millimeter Array: Imaging Cosmic Dawns” |
ABSTRACT:
| The Atacama Large Millimeter Array (ALMA), a project of the National Radio Astronomy Observatory and the European Southern Observatory, will be built over the coming decade in Northern Chile. ALMA will be a revolutionary telescope, operating at millimeter and submillimeter wavelengths and comprised of an array of individual antennas each 12 meters in diameter that work together to make precision images of astronomical objects. The goal of the ALMA Project is an array of 64 antennas that can be positioned as needed over an area 10 kilometers in diameter so as to give the array a zoom-lens capability. ALMA will image the universe with unprecedented sensitivity and sharpness at millimeter and submillimeter wavelengths. The energy density of radiation from both the Milky Way and from the diffuse extragalactic background peaks in the submillimeter. Aside from Cosmic Microwave Background photons, submillimeter photons are the most abundant photons in the Universe. Detailed imaging at these wavelengths will be a major step for astronomy, making it possible to study the origins of galaxies, stars and planets. |
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