Physics at the University Of Virginia
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Seminars for the week of
4/21/2014 - 4/25/2014

Atomic Research Seminar & GPSA Talk
Monday, April 21 Oat Arpornthip [Host: Cass Sackett]
3:30 PM, Room 204 University of Virginia
Physics Building “A compact vapor cell for cold atom applications”
 Atom traps promise great improvements on a wide range of technologies: Atom interferometry, gravimetry, magnetometry, navigation. Despite orders of magnitude in improvements promised, atom technology has seen limited commercial adoption due to voluminous instrumentation size. We have designed a new type of trap which reduces the apparatus volume by a factor of ten with satisfactory performance. Our design choices and component research will be discussed. We aim to develop a self-contained Rb vapor cell capable of sustaining a magneto-optical trap at a decent background pressure over a long period of time.

Tuesday, April 22 Available
3:30 PM, Room 204
Physics Building

Condensed Matter
Wednesday, April 23
Note Special Day
Kun Woo Kim [Host: Israel Klich]
11:00 AM, Room 210
Note Special Time and/or Room
Physics Building “Effect of surface disorder on transport in topological insulators”
 What is the effect of surface-only disorder on the electronic states of a 3d TI? The layers in the clean bulk parallel to surface probe the surface impurities as they hop in and out of the surface layer. A recursive treatment of the impurity effects is made possible through successive elimination of the lattice layer by layer. This leads to non-linear renormalization group flow of an effective surface impurity potential. We found an exact mapping between the recursion relation and Schrodinger equation along the layers, therefore the modified self energy due to surface impurity could be simply obtained from the transfer matrix method. As a concrete example of 2d topological insulator, we found the exact expression of on-layer self energy for a clean system and an asymptotic expression that captures a general behavior of layers deep in the bulk.

High Energy
Wednesday, April 23 RESERVED
3:30 PM, Room 204
Physics Building

Condensed Matter
Thursday, April 24 Jean-Damien Pillet [Host: Tom Gallagher]
3:30 PM, Room 204 Columbia University
Physics Building “Amplification, entanglement and storage of microwave radiation using superconducting circuits”
 Microwave signals have appeared during the last decade as a powerful and versatile platform to investigate a wide variety of quantum phenomena, from fundamental quantum optics to more oriented researches toward quantum information processing. This specific place originates from the fact that microwave signals can on one hand be precisely tailored and controlled with standard commercial electronics. On the other hand they can easily be processed at the single photon level in the quantum regime by superconducting circuits cooled down to dilution fridge temperatures thanks to a unique component, the Josephson junction, an intrinsic non dissipative lumped non-linear inductor.

I will present how we designed and built a superconducting circuit, based on a Josephson ring modulator (JRM), a ring of 4 Josephson junctions in a Wheatstone bridge configuration, allowing non-degenerate three wave-mixing. I will show that, when pumped at the appropriate frequency, this single circuit behaves as a tunable beam splitter with frequency conversion, a quantum limited amplifier or an EPR states generator. Using frequency conversion, we demonstrate on demand capture, storage and release of microwave radiations with approx. 80% catching efficiency and about 30 storage operations per memory lifetime. We then demonstrate entanglement generation between a propagating microwave mode and a localized mode in the cavity.

Friday, April 25 Seth Putterman [Host: Israel Klich]
3:30 PM, Room 204 UCLA
Physics Building “Unknowns of energy concentrating phenomena”
 The path to equilibrium is not controlled by entropy production. Although entropy increases with every time step, dynamical motion can be dominated by nonlinear physical processes that spontaneously concentrate energy density. In sonoluminescence a bubble concentrates the energy of a traveling sound wave by 12 orders of magnitude to create picoseconds flashes of blackbody radiation that originate in a new state of matter. When surfaces are brought into and out of contact they exchange charge: a process called tribo-electrification. This phenomenon can be so strong that the power applied to peel sticky tape is efficiently transduced into a flux of high energy electrons, and x-ray photons that can expose an image in a few seconds. For a ferroelectric crystal, instabilities in the phonon spectrum lead to a spontaneous polarization that for Lithium Niobate reaches 15.million volts per cm. The temperature dependence of this field can be used to build a neutron generator based on the fusion of deuterium nuclei. These phenomena challenge a reductionist approach to the theoretical physics of emergent phenomena. The degree to which the energy density of a continuous system can be concentrated by off-equilibrium motion has not been determined by theory. For sonoluminescence, we do not know if the parameter space includes a region where an extra factor of 100 in energy density makes it possible to realize thermonuclear fusion. For triboelectrification, we do not have an ab-initio theory of charge transfer. And for ferroelectrics we do not have an ab-initio theory of the limits of spontaneous polarization which can be designed.