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Colloquia This Term

ics Special Colloquium


Wednesday, January 18, 2017
3:30 PM
Physics Building, Room 204
Note special date.
Ilias Cholis [Host: Peter Arnold]
Johns Hopkins University
"Searching for Dark Matter in Gravitational Waves"
 
 Slideshow (PDF)
ABSTRACT:

The nature of dark matter is one of the most longstanding and puzzling questions in physics. With cosmological measurements we have been able to measure its abundance with great precision. Yet, what dark matter is composed of remains a mystery.

In 2016 the first ever observation of gravitational waves from the coalescence event of two black holes was achieved by the LIGO interferometers.

Together with my collaborators we recently advocated that the interactions of 30 solar masses primordial black holes composing the dark matter could explain this event.

This opens up a new window in indirect searches for dark matter.

In my talk, I will discuss the various probes to distinguish between these mergers of primordial black holes, from the more traditional astrophysical black hole binaries.

One is through their mass spectrum, another is through cross-correlation of gravitational events with future overlapping galaxy catalogs. A third, is through their contribution to the stochastic gravitational wave background. Finally a fourth probe uses the fact that primordial black black holes form binaries with highly eccentric orbits. Those will then merge on timescales that in some cases are years, days or even minutes, retaining some eccentricity in the last seconds before the merger, which can be detected by LIGO and future ground based interferometers.

SLIDESHOW:
ics Colloquium
Friday, January 27, 2017
3:30 PM
Physics Building, Room 204
Available [Host: ]
ics Special Colloquium


Wednesday, February 1, 2017
3:30 PM
Physics Building, Room 204
Note special date.
Anna Ijjas [Host: Peter Arnold]
Princeton University
"Bouncing"
 
 Slideshow (PDF)
ABSTRACT:

In this talk, I will focus on cosmologies that replace the big bang with a big bounce. I will explain how, in these scenarios, the large-scale structure of the universe is determined during a contracting phase before the bounce and will describe the recent development of the first well-behaved classical (non-singular) cosmological bounce solutions.

SLIDESHOW:
ics Special Colloquium


Tuesday, February 7, 2017
3:30 PM
Physics Building, Room 204
Note special date.
Renee Horton
NASA
"The Art of Metal Joining and How It's Used NASA Michoud Assembly Facility"
 
 Slideshow (PDF)
ABSTRACT:

Metal joining is a controlled process used to fuse metals. There are several techniques of metal joining of which friction stir welding is one of the more basic forms. Friction stir welding is an innovative weld process that continues to grow in use, in the commercial, defense, and space sectors. It produces high quality and high strength welds in aluminum alloys. The process consists of a rotating weld pin tool that plasticizes material through friction. The plasticized material is welded by applying a high weld forge force through the weld pin tool against the material during pin tool rotation.  Self-reacting friction stir welding (SR-FSW) is one variation of the FSW process developed at the National Aeronautics and Space Administration (NASA) for use in the fabrication of propellant tanks and other areas used on the Space Launch System (SLS)

 

NASA's SLS is an advanced, heavy-lift launch vehicle which will provide an entirely new capability for science and human exploration beyond Earth's orbit. The SLS will give the nation a safe, affordable and sustainable means of reaching beyond our current limits and open new doors of discovery from the unique vantage point of space.

SLIDESHOW:
ics Colloquium
Friday, February 10, 2017
3:30 PM
Physics Building, Room 204
Andrey Chubukov [Host: Genya Kolomeisky]
University of Minnesota
"Superconductivity from repulsion"
 
 Slideshow (PDF)
ABSTRACT:

In my talk, I review recent and not so recent works aiming to understand whether a nominally repulsive Coulomb interaction can by itself give rise to a superconductivity.  I discuss a generic scenario of the pairing by electron-electron interaction, put forward by Kohn and Luttinger back in 1965, and  modern studies of  the electronic mechanisms of superconductivity in the lattice systems which model cuprates,  Fe-pnictides, and  doped graphene.  I show that the pairing in all three classes of materials can be viewed as a lattice version of Kohn-Luttinger physics, despite that the pairing symmetries are different.  I discuss under what conditions the pairing occurs and rationalize the need to do  renormalization-group studies.  I also discuss the interplay between superconductivity and density-wave instabilities.

SLIDESHOW:
ics Special Colloquium


Wednesday, February 15, 2017
3:30 PM
Physics Building, Room 204
Note special date.
Kent Yagi [Host: Peter Arnold]
Princeton University
" Probing Extreme Gravity with Black Holes and Neutron Stars"
 
 Slideshow (PDF)
ABSTRACT:

Black holes and neutron stars are extremely compact astrophysical objects that are produced after the death of very massive stars. Due to their large compactness and population, such compact objects offer us excellent testbeds for probing fundamental physics. In this talk, I will focus on probing extreme (strong and dynamical-field) gravity that was previously inaccessible. Regarding black hole based tests of gravity, I will explain how stringently one can probe various fundamental pillars in General Relativity with the recently-discovered gravitational wave events. Regarding neutron star based tests of gravity, I will use approximate universal relations ("I-Love-Q relations") among certain neutron star observables that are almost insensitive to the unknown stellar internal structure, and describe how one can probe extreme gravity by combining future gravitational wave and binary pulsar observations. I will conclude with a summary of important future directions.

SLIDESHOW:
ics Special Colloquium


Thursday, February 16, 2017
3:30 PM
Physics Building, Room 204
Note special date.
Yi-Zhuang You [Host: Israel Klich ]
Harvard University
"Bosonic Symmetry Protected Topological States: Theory, Numerics, and Experimental Platform"
ABSTRACT:

Topological phases of matter is an active research area of condensed matter physics. Among various topics, the bosonic symmetry protected topological (BSPT) states have attracted enormous theoretical interest in the last few years. BSPT states are bosonic analogs of topological insulators. The Haldane phase of spin-1 chains is one famous example. I will talk about our recent proposal to realize two-dimensional BSPT states in the twisted bilayer graphene with strong magnetic field, as well as numerical simulations of the lattice model in various parameter regimes. The proposed BSPT state is a quantum spin Hall insulator with bosonic boundary modes only. The bosonic modes are spin and charge collective excitations of electrons. The quantum phase transition between the topological and the trivial phases happens by closing the gap of bosonic modes in the bulk, without closing the single particle gap of electrons, which is fundamentally different from all the well-known topological transitions in free fermion topological insulators. On the theory side, the phase transition is related to topics of deconfined criticality and duality of (2+1)D conformal field theories. The theoretical, numerical and experimental studies will deepen our understanding of quantum phase transitions.

**THE RECEPTION WILL BE HELD AT 3:00PM IN ROOM 313**

ics Special Colloquium


Wednesday, February 22, 2017
3:30 PM
Physics Building, Room 204
Note special date.
Michele Vallisneri [Host: Peter Arnold]
Jet Propulsion Laboratory, Caltech
"Gravitational waves from binary black holes across the spectrum"
 
 Slideshow (PDF)
ABSTRACT:

On September 14, 2015, the two LIGO detectors simultaneously observed a transient gravitational-wave signal, which was named GW150914. The signal fit very precisely the general-relativistic prediction for the inspiral, merger, and ringdown of a pair of stellar-mass black holes, with component masses greater than was thought possible in standard evolution scenarios. This was the first direct detection of gravitational waves and the first observation of a binary black-hole merger. I describe the mechanics and behind-the-scenes of the detection, and its implications for astrophysics and fundamental physics. Two additional black-hole binaries were detected in LIGO's first observing run, and more are expected from current data taking. At the low-frequency side of the gravitational-wave spectrum, signals from massive black-hole binaries are targeted by the space-based observatory LISA, now on track for launch in the early 2030s, and by pulsar-timing arrays, with a positive detection expected in ten years. I discuss the science case, prospects, and requirements of these programs.

**THE RECEPTION WILL BE HELD AT 3:00PM IN ROOM 313**

SLIDESHOW:
ics Special Colloquium


Thursday, February 23, 2017
3:30 PM
Physics Building, Room 204
Note special date.
Torsten Karzig [Host: Israel Klich ]
Station Q, UCSB
"Progress and challenges in designing a universal Majorana quantum computer"
ABSTRACT:

I will discuss a promising design proposal for a scalable topological quantum computer. The qubits are envisioned to be encoded in aggregates of four or more Majorana zero modes, realized at the ends of topological superconducting wire segments that are assembled into superconducting islands with significant charging energy. Quantum information can be manipulated according to a measurement-only protocol, which is facilitated by tunable couplings between Majorana zero modes and nearby semiconductor quantum dots. The key virtue of the proposed architecture is its modular and scalable design and a natural suppression of quasiparticle poisoning by charge protection.

In the second part of the talk I will comment on the importance of elevating these designs to full quantum universality by so called magic state injection. The latter relies on a high fidelity source of specific quantum states and I will point out some of ideas and challenges for providing them.

**THE RECEPTION WILL BE HELD AT 3:00PM IN ROOM 313**

ics Colloquium
Friday, February 24, 2017
3:30 PM
Physics Building, Room 204
RESERVED
ics Special Colloquium


Monday, February 27, 2017
3:30 PM
Physics Building, Room 204
Note special date.
Adrian Liu [Host: Peter Arnold]
UC Berkeley
"The Past, Present, and Future of 21cm Cosmology"
 
 Slideshow (PDF)
ABSTRACT:

In the next few years, low-frequency radio telescopes will use the 21cm line of neutral hydrogen to make unprecedentedly large maps of our observable Universe. These will provide exquisite constraints on the properties of the first stars and galaxies. Along these lines, I will review recent results from the Precision Array to Probe the Epoch of Reionization (PAPER) experiment, which have begun to shed light on heating processes in the early universe. I will also discuss how comparing theory and observations will become difficult as one enters the regime of “big data” and theoretical models become increasingly complicated. I will describe how machine learning techniques make such comparisons computationally feasible. Finally, I will discuss the recently commenced Hydrogen Epoch of Reionization Array (HERA) experiment, including its forecasted ability to constrain fundamental parameters such as the neutrino mass. Looking to the future, I will highlight additional opportunities to constrain cosmology and particle physics using the 21cm line.

 

SLIDESHOW:
ics Special Colloquium


Tuesday, February 28, 2017
3:30 PM
Physics Building, Room 204
Note special date.
Mark Rudner [Host: Israel Klich ]
"Quantum alchemy for the 21st century: accessing new horizons of quantum many-body dynamics through periodic driving"
ABSTRACT:

Recent work on topological materials has revealed a wide variety of intriguing phenomena that may arise when particles move in "non-trivial" bands.  At the same time, modern advances in experimental capabilities for controlling electronic, atomic, and optical systems open new possibilities for dynamically controlling the behaviors of a range of quantum systems. In this talk I will review the basic ideas behind topological band theory, and then explain how periodic driving can be used to gain dynamical control over the topological properties of quantum matter.  In the driven case, intriguing new types of robust non-equilibrium topological phenomena emerge. To illustrate, I will show how the combination of driving, topology, and interactions can bring about a new regime of universal quantized transport, and discuss potential near-term experimental realizations.

**THE RECEPTION WILL BE HELD AT 3:00PM IN ROOM 313**

ics Special Colloquium


Wednesday, March 1, 2017
3:30 PM
Physics Building, Room 204
Note special date.
Francois Foucart [Host: Peter Arnold]
Lawrence Berkeley National Lab
"From Chirps to Jets: The extreme world of Black Holes and Neutron Stars"
 
 Slideshow (PDF)
ABSTRACT:

Black holes and neutron stars are extraordinary astrophysical laboratories.

They allow us to test the laws of gravity and nuclear physics in extreme environments which cannot be reproduced on Earth. In this talk, I will discuss efforts to model these compact objects in two classes of astrophysical systems: mergers of black hole-neutron star and neutron star-neutron star binaries, and accretion disks around supermassive black holes. The first are powerful sources of gravitational waves, and emit bright electromagnetic transients. In the advanced gravitational wave detector era, they will provide us with new information about general relativity, the properties of matter above nuclear density, and the population of black holes and neutron stars. The second will soon be imaged by the Event Horizon Telescope with enough accuracy to resolve the horizon of two black holes, and to study the behavior of the nearly collisionless plasma accreting onto them. I will in particular focus on the role of numerical simulations using general relativistic codes, which will play a crucial role in our interpretation of these upcoming observations.

 

SLIDESHOW:
ics Colloquium
Friday, March 17, 2017
3:30 PM
Physics Building, Room 203
Note special room.
Bill Phillips [Host: Sanjay Khatri - OSA Student Chapter]
NIST
"Manipulating atoms with light: from spectroscopy to atomtronics"
ABSTRACT:

Physicists have used light and its polarization to elucidate the internal state of atoms since the 19th century.  Early in the 20th century, the momentum of light was used to change the center-of-mass motion of atoms.  The latter part of the 20th century brought optical pumping, coherent laser excitation, and laser cooling and trapping as tools to manipulate both the internal and external states of atoms.  Atom optics techniques like diffraction of atoms from light provided the elements needed for atom-wave interferometers.  Bose-Einstein condensation created atomic samples having laser-like deBroglie-wave coherence.   Now, in the 21st century, the circulation of superfluid atoms in ring-shaped structures enables “atomtronic” circuitry—an atomic analog of superconduction electric circuits.  We observe persistent flow of atoms in toroidal traps, and can introduce a weak-link (a kind of Josephson junction) that allows control of the quantized circulation of atoms. 

VIDEO:
ics Special Colloquium


Thursday, March 23, 2017
7:00 PM
The Rotunda, Room Dome Room
Note special date.
Note special time.
Note special room.
Francis Halzen [Host: Craig Group]
UW - Wisconsin
"Ice Fishing for Neutrinos at the South Pole"
ABSTRACT:

The IceCube project at the South Pole has melted eighty-six holes over 1.5 miles deep in the Antarctic icecap for use as astronomical observatories. The project recently discovered a flux of neutrinos reaching us from the cosmos, with energies more than a million times those of the neutrinos produced at accelerator laboratories. These neutrinos are astronomical messengers from some of the most violent processes in the universe--giant black holes gobbling up stars in the heart of quasars and gamma-ray bursts, the biggest explosions since the Big Bang.

In a special public lecture, brought to you by the departments of physics, astronomy, and NRAO Francis Halzen, Gregory Breit Professor and Hilldale Professor of Physics at UW-Madison and the principal investigator of IceCube, will tell the story of the IceCube telescope and discuss highlights from recent scientific results.

 

ics Colloquium
Friday, March 24, 2017
3:30 PM
Physics Building, Room 204
Ariel Amir [Host: Marija Vucelja]
Harvard University
"Controlling cell size and DNA replication in bacteria - insights from mathematical modeling"
ABSTRACT:

Understanding how cells control and coordinate the various ongoing cellular processes, such as DNA replication, growth and division is an outstanding fundamental problem in biology. Remarkably, bacterial cells may divide faster than their chromosomes replicate, implying that cells maintain multiple rounds of chromosome replication, and that tight control over DNA replication must be in place. I will show how ideas from statistical mechanics and mathematical modeling can serve as alternative "microscopes" into this problem. Our results suggest that both cell size and chromosome replication may be simultaneously regulated by following a simple control mechanism, in which, effectively, a constant volume is added between two DNA replication initiation events. This model elucidates the experimentally observed correlations between various events in the cell cycle, and explains the exponential dependence of cell size on the growth rate, as well as recent experiments in which cell morphology is perturbed.

http://amir.seas.harvard.edu/

ics Colloquium
Friday, March 31, 2017
3:30 PM
Physics Building, Room 204
Kirsten Tollefson [Host: Chris Neu]
Michigan State University
"A New Way to Look at the Sky"
ABSTRACT:

The High Altitude Water Cherenkov (HAWC) Gamma-ray Observatory was completed in March 2015 and is now giving us a new view of the sky. HAWC is a continuously operating, wide field-of-view observatory sensitive to 100 GeV – 100 TeV gamma rays and cosmic rays. It is 15 times more sensitive than previous generation extensive air shower gamma-ray instruments. It serves as a “finder” telescope and monitors the same sky as gamma-ray satellites (Fermi), gravity-wave (LIGO) detectors and neutrino observatories (IceCube) allowing for multi-wavelength and multi-messenger observations.  HAWC hopes to answer questions such as "what is dark matter?” and “where do cosmic rays come from?” by observing some of the most violent processes in our Universe. I will present highlights from HAWC’s first year of operation.

ics Colloquium
Friday, April 7, 2017
3:30 PM
Physics Building, Room 204
Maxim Olshanii [Host: Israel Klich ]
University of Massachusetts
"TBA"
ics Colloquium
Friday, April 14, 2017
3:30 PM
Physics Building, Room 204
Gregory Falkovich [Host: Marija Vucelja]
Weizmann Institute
"Negative resistance and other wonders of viscous electronics in graphene"
ABSTRACT:

Quantum-critical strongly correlated systems feature universal collision-dominated collective transport. Viscous electronics is an emerging field dealing with systems in which strongly interacting electrons flow like a fluid. We identified vorticity as a macroscopic signature of electron viscosity and linked it with a striking macroscopic DC transport behavior: viscous friction can drive electric current against an applied field, resulting in a negative resistance, recently measured experimentally in graphene. I shall also describe current vortices, expulsion of electric field, conductance exceeding the fundamental quantum-ballistic limit and other wonders of viscous electronics. Strongly interacting electron-hole plasma in high-mobility graphene affords a unique link between quantum-critical electron transport and the wealth of fluid mechanics phenomena.

http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys3667.html

https://arxiv.org/abs/1607.00986  

http://arxiv.org/abs/1607.07269

ics Colloquium
Friday, April 21, 2017
3:30 PM
Physics Building, Room 204
Nora Berrah [Host: Despina Louca]
University of Connecticut
"Probing Molecular Dynamics from Within using FELs"
ABSTRACT:

Short x-ray pulses from free electron lasers (FELs) open a new regime for all scientific research. The first x-ray FEL, the Linac Coherent Light Source (LCLS) at the SLAC National Laboratory on the Stanford campus, provides intense short pulses that allow the investigation of ultrafast non-linear and multi-photon processes, including time-resolved investigations in molecules. We will report on the femtosecond response of molecules to the ultra-intense, ultrafast x-ray radiation from FELs as well as on time-resolved investigation using x-ray pump-x-ray probe techniques.

ics Colloquium
Friday, April 28, 2017
3:30 PM
Physics Building, Room 204
John Beacom [Host: Craig Group]
Ohio State
"Making Neutrino Astronomy Real"
ABSTRACT:

For over 50 years, people have been discussing the promise of high-energy neutrino astronomy.  For most of that time, wholesale theoretical conjecture was unmatched by even a trifling return of measured experimental facts.  Then in 2013, the IceCube neutrino observatory discovered astrophysical neutrinos with energies up to fifteen orders of magnitude above those of visible light.  What does this mean for understanding astrophysical sources, the properties of neutrinos, and the contents of the Universe?

Colloquia and Special Lectures Committee
Cass Sackett (Chair)
Gordon Cates (Member)
Bob Hirosky (Member)
Bob Jones (Member)
Marija Vucelja (Member)
Nilanga Liyanage (Ex-Officio)

To add a speaker, send an email to cas8m@Virginia.EDU Include the seminar type (e.g. Colloquia), date, name of the speaker, title of talk, and an abstract (if available). [Please send a copy of the email to phys-speakers@Virginia.EDU.]