Anatoli Polkovnikov, Boston University
"Quantum dynamics in low dimensional isolated systems"

In the first part of this talk I will discuss relations between quantum and thermodynamic adiabatic theorems. In paticular, I will argue that generically there are three different regimes of a system response to a slow quench. These regimes are characterized by different types of scaling of the heating induced in the system with the quench rate: A) analytic, B) non-analytic, and C) non-adiabatic. In the latter regime the limits of quench rate going to zero and the system size going to infinity do not commute. I will discuss how these findings can be probed in cold atom experiments. In addition I will discuss general structure of the expansion of dynamics of isolated systems around the classical limit in quantum fluctuations. I will illustrate this approach with a few examples. In particular, I will discuss dynamics and thermalization in a quantum version of the Fermi-Pasta-Ulam problem and its atomic counterpart, which can be realized in optical lattices.

Belen Paredes, University of Mainz
"Minimum instances of topological matter in an optical plaquette"

Sankar Das Sarma, University of Maryland
Computing with Quantum Knots: Non-Abelian Anyons and Topological Quantum Computation

Ordinary quantum computation uses simple quantum two level systems (e.g. electron or nuclear spins, atomic hyperfine states, etc.) as quantum bits (’qubits’) with one- and two-qubit unitary operations serving as universal quantum gates. The main problem is quantum decoherence, the inevitable continuous dephasing of a quantum state due to its interaction with the environment. A revolutionary alternative idea is to build a quantum computer which is topologically immune to quantum decoherence. Such an inherently fault tolerant topological quantum computer is completely protected from any local perturbation induced by the environment and uses the time-space braiding (i.e. creating suitable quantum knots) of non-Abelian anyonic quasiparticles for quantum computation. Prospects for topological quantum computation will be discussed in this talk from a combined experimental and theoretical perspective. I will discuss a number of physical systems, mostly the fractional quantum Hall states in high-mobility two-dimensional semiconductor structures, but also chiral p-wave superconductors, p-wave fermionic superfluids, cold atom optical lattices, frustrated quantum magnetic systems, Josephson junction arrays, rotating BEC systems, etc. where the possibility for doing topological quantum computation has been theoretically discussed in the recent literature. I will also provide an elementary introduction to the concepts of topological phase, anyons, and non-Abelian braiding statistics, discussing how the interdisciplinary subject of topological quantum computation brings together topology, conformal field theory, fractional quantum Hall effect, ultra-cold atoms, p-wave superconductivity, Chern-Simons-Witten theory, and materials science.
Further reading: Charles Day, Physics Today, October 2005; Graham Collins, Scientific American, April 2006; Sankar Das Sarma, Michael Freedman, and Chetan Nayak, Physics Today, July 2006; Sankar Das Sarma, Michael Freedman, Chetan Nayak, Steven Simon, and Ady Stern, http://www.arxiv.org/abs/0707.1889 (to appear in Reviews of Modern Physics 2008).

Prof. V.G. Veselago, Prokhorov Institute of General Physics, Moscow
“Some Additional Remarks about Electrodynamics of LHM”

Special Time and Place
12:00, Jefferson 453, Bring your lunch drinks and dessert will be provided.

Matthias Weidemuller, Physics Institute, Albert-Ludwig University Freiburg, Germany
“Rydberg Matter”- Many-body phenomena in an ultracold gas of Rydberg atoms

Due to the long-range character of the interaction between highly excited atoms, the dynamics of an ultracold gas of Rydberg atoms is entirely determined by van-der-Waals and dipole-dipole interactions. One outstanding property is the tunability of the strength and the character of the dipolar interactions. This opens the exciting possibility to explore the transition from a weakly coupled two-body system to a strongly coupled many-body system. The long-range interactions lead to many-body entanglement and has possible applications in quantum computing. In a recent series of experiments we studied coherent many-body phenomena in an ultracold gas of Rydberg atoms. We could observe the so-called dipole blockade, i.e. an interaction-induced suppression of excitation. Our experiments also reveal the role of interaction-induced mechanical forces over distances exceeding 10 mm. The talk will give an introduction into the field of ultracold Rydberg gases and an overview over latest developments.

Olga Kocharovskaya
Coherent Control of the Atomic Optical and Nuclear Gamma-Ray Transitions in Solids      

      In the last decade there has been an essential progress in coherent control of both linear and nonlinear material optical responses. One approach developed for multilevel quantum systems is based on resonant excitation of atomic coherence at the transition adjacent to those coupled with light. Such coherence provides multiple interfering absorption paths for light, leading to many interesting effects: Coherent Population Trapping , Electromagnetically Induced Transparency (EIT), Slow Light , Lasing Without Inversion , etc..
     So far most of theoretical and experimental studies were dealing with the gaseous media. I shall review recent progress in extension of this field of research from gaseous to solid media including both (i) optical electronic and (ii) gamma-ray nuclear transitions

It includes

• experimental realizations of EIT and Ramsey fringes at the optical transitions in room-temperature solids;
• coherent control of the excited state absorption in laser crystals via EIT  and prospects for development of tunable and/or femto-second solid-state lasers especially in UV and VUV frequency ranges;
• experimental realization of EIT at the gamma-ray nuclear transitions via the nuclear level anti-crossing;
• modification of the nuclear absorption under the action of the laser radiation;
• coherent control of the inhomogeneous line broadening at the gamma-ray nuclear and atomic optical transitions.
       Finally, I shall briefly review the current status of the gamma-ray laser problem.

Eric Akkerman, Technion
Photon localization and Dicke superradiance : a cross-over to small world networks

Abstract: We study photon localization in a gas of cold atoms, using a Dicke Hamiltonian that accounts for photon mediated atomic dipolar interactions. The photon escape rates are obtained from a new class of random matrices. A scaling behavior is observed for photons escape rates as a function of disorder and system size. Photon localization is described using statistical properties of random networks which display a "small world" cross-over. Those results are compared to the Anderson photon localization transition.

Mukund Vengalattore , UC-Berkeley
Postponed

Dr. Thomas Giesen, I. Physikalisches Institut, University of Cologne, Germany
Terahertz Spectroscopy for Astrophysical Applications

Abstract: High resolution Terahertz (THz) spectroscopy is a vivid field of current research due to its importance for astrophysics and molecular physics. The continuous development and fabrication of monochromatic sub-millimeter wave radiation sources is the key to recent success of THz spectroscopy in laboratory and space. At the Cologne laboratories high resolution spectrometers based on backward wave oscillators, multiplier techniques and quantum cascade lasers are currently used for laboratory studies at frequencies up to 3 THz. A number of molecules which are of particular astrophysical relevance have been studied, including small transient species, such as radicals (Cn, n=3, 4, 5,.., C3H) and molecular ions (H2D+, D2H+) as well as less reactive species with complicated spectra due to internal motions (CH3OCH3).

New THz telescope facilities like ALMA, Herschel, and SOFIA will make use of accurate laboratory data to identify interstellar molecules in various types of astrophysical sources and to probe a wide range of physical and chemical conditions.

Fall Term 2008

Maxim Olshanii, University of Massachusetts, Boston
Eigenstate thermalization hypothesis and quantum thermodynamics

Abstract:
One of the open questions in quantum thermodynamics reads: how can linear quantum dynamics provide chaos necessary for thermalization of an isolated quantum system?

To this end, we perform an ab initio numerical analysis of a system of hard-core bosons on a lattice and show [Marcos Rigol, Vanja Dunjko & Maxim Olshanii, Nature 452, 854 (2008)] that the above controversy can be resolved via the Eigenstate Thermalization Hypothesis suggested by Deutsch [J. M. Deutsch, Phys. Rev. A 43, 2046 (1991)] and Srednicki [M. Srednicki, Phys. Rev. E 50, 888 (1994)]. According to this hypothesis, in quantum systems thermalization happens in each individual eigenstate of the system separately, but it is hidden initially by coherences between them. In course of the time evolution the thermal properties become revealed through (linear) decoherence that need not to be chaotic.

David Cory, MIT
Error Finding and Control for Quantum Processors

Abstract:
The promised benefits of future quantum information processors rests on their ability to maintain and manipulate coherent information. This talk will attempt to connect theories of fault tolerant quantum computation to experimental examples of quantum error correction. In particular I will discuss the role of error finding and ask what are the essential characteristic of errors that should be experimentally measured to show that fault tolerance theories are useful/relevant and to tailor quantum error correction methods to actual error models.

 

Paul Lett, NIST
Entangling images with four-wave mixing

 

Thad Walker, University of Wisconsin-Madison
Observation of Rydberg Blockade between Pairs of Atoms

Markus Aspelmeyer, University of Vienna