Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session J45: Focus Session: Non-equilbrium Physics with Cold Quantum Gases |
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Sponsoring Units: DAMOP Chair: Miguel Angel Garcia March, Colorado School of Mines Room: A310 |
Tuesday, March 22, 2011 11:15AM - 11:51AM |
J45.00001: Universal Dynamics Near Quantum Critical Points Invited Speaker: asp@physics.bu.edu [Preview Abstract] |
Tuesday, March 22, 2011 11:51AM - 12:03PM |
J45.00002: Dynamics of a finite-rate quantum quench in an ultra-cold atomic BCS superfluid Chih-Chun Chien, Bogdan Damski We study dynamics of an ultra-cold atomic BCS superfluid driven towards the BCS superfluid-Fermi liquid quantum critical point by a gradual decrease of the pairing interaction. We analyze how the BCS superfluid falls out of equilibrium and show that the non-equilibrium gap and Cooper pair size reflect critical properties of the transition. We observe three stages of evolution: adiabatic where the Cooper pair size is inversely proportional to the equilibrium gap, weakly non-equilibrium where it is inversely proportional to the non-equilibrium gap, and strongly non-equilibrium where it decouples from both equilibrium and non-equilibrium gap. These phenomena should stimulate future experimental characterization of non-equilibrium ultra-cold atomic BCS superfluids. [Preview Abstract] |
Tuesday, March 22, 2011 12:03PM - 12:15PM |
J45.00003: Slow quench dynamics of a trapped one-dimensional Bose gas confined to an optical lattice Jean-Sebastien Bernier, Guillaume Roux, Corinna Kollath We analyze the effect of a linear time-variation of the interaction strength on a trapped one-dimensional Bose gas confined to an optical lattice. The evolution of different observables such as the experimentally accessible onsite particle distribution are studied as a function of the ramp time using time-dependent exact diagonalization and density-matrix renormalization group techniques. We find that the dynamics of a trapped system typically display two regimes: for long ramp times, the dynamics are governed by density redistribution, while at short ramp times, local dynamics dominate as the evolution is identical to that of an homogeneous system. In the homogeneous limit, we show that the energy absorbed scales non-trivially with the ramp time. [Preview Abstract] |
Tuesday, March 22, 2011 12:15PM - 12:27PM |
J45.00004: Quench dynamics of paired states of fermions in two dimensions with breaking of parity and time-reversal symmetries Noah Bray-Ali Resonantly paired fermions in two spatial dimensions with breaking of parity and time-reversal symmetry are believed to exhibit two topologically distinct phases at low temperature: the weak-pairing (Bardeen-Cooper-Schrieffer or BCS) phase and the strong-pairing (Bose-Einstein condensate or BEC) phase. We examine the dynamic response of each phase to a rapid quench towards and away from the quantum critical regime. The weak-pairing (BCS) phase has a higher residual defect concentration after the quench than the strong-pairing (BEC) phase. We relate this to the presence of a topologically protected, Majorana fermion edge excitation in the weak-pairing phase, and propose quench dynamics as a practical, experimental probe of this excitation in these systems. [Preview Abstract] |
Tuesday, March 22, 2011 12:27PM - 12:39PM |
J45.00005: Title: Time-Dependent Mean Field Theory for Quench Dynamics in correlated electron systems Marco Schiro', Michele Fabrizio A simple and very flexible variational approach to the out-of-equilibrium quantum dynamics in strongly correlated electron systems is introduced through a time-dependent Gutzwiller wavefunction. As an application, we study the simple case of a sudden change of the interaction in the fermionic Hubbard model and find at the mean field level an extremely rich behaviour. In particular, a dynamical transition between small and large quantum quench regimes is found to occur at half-filling, in accordance with the analysis of Eckstein {\sl et al.}, Phys. Rev. Lett. {\bf 103}, 056403 (2009), obtained by dynamical mean field theory, that turns into a crossover at any finite doping. [Preview Abstract] |
Tuesday, March 22, 2011 12:39PM - 12:51PM |
J45.00006: Non-equilibrium dynamics and heating of cold atoms in optical lattices Andrew Daley, Hannes Pichler, Peter Zoller We study the dissipative many-body dynamics of cold atoms in optical lattices that is induced by incoherent scattering of light from the lattice lasers. The resulting heating process is intrinsically non-equilibrium, and involves an important interplay between the atomic physics of the spontaneous emission process and the many-body physics of the state present in the system. In particular, we observe important differences for strongly and weakly interacting regimes, as well as a strong dependence on the sign of the laser detuning from the excited atomic state. We compute heating rates and changes to characteristic correlation functions based on a microscopic master equation. In 1D this equation can be propagated exactly by combining time-dependent density matrix renormalization group (t-DMRG) methods with quantum trajectory techniques. [Preview Abstract] |
Tuesday, March 22, 2011 12:51PM - 1:03PM |
J45.00007: Quantum effects on Fermi-Pasta-Ulam recurrence in ultracold lattice bosons Ippei Danshita, Rafael Hipolito, Vadim Oganesyan, Anatoli Polkovnikov We propose an experimental scheme for studying the Fermi-Pasta-Ulam (FPU) problem in a quantum mechanical regime with use of ultracold one-dimensional Bose gases in an optical lattice. In the classical limit, we identify parameter regions in which FPU recurrence can occur in this system. The strength of quantum fluctuations can be widely controlled by tuning the number of atoms per lattice sites (filling factor). To investigate the effects of quantum fluctuations on the FPU recurrence, we simulate the real time dynamics of the Bose-Hubbard model by means of the exact numerical method of time-evolving block decimation. We show that strong quantum fluctuations cause significant damping of the FPU oscillation. [Preview Abstract] |
Tuesday, March 22, 2011 1:03PM - 1:15PM |
J45.00008: Dynamic Stimulation of Phase Coherence in Lattice Bosons Andrew Robertson, Victor Galitski, Gil Refael The existence of superfluidity depends on the energy distribution of~excitations in a system. However, the distribution at thermal equilibrium is rarely optimal for the manifestation of long-range phase coherence. We show that by pushing a system of lattice bosons out of equilibrium with periodic driving, it is possible to increase or decrease the phase coherent region in the phase diagram of the Bose-Hubbard model.~We demonstrate this by calculating the non-equilibrium spatial correlation function~using a synthesis of Keldysh and Floquet theories. This work is supported by DARPA-MTO. [Preview Abstract] |
Tuesday, March 22, 2011 1:15PM - 1:27PM |
J45.00009: Phase Kink Dynamics in fluctuating Bose condensates Amy Cassidy, Ludwig Mathey, Charles Clark We study the dynamics of Bose gases following a phase imprint. Numerical results within truncated Wigner approximation, which includes both quantum and thermal fluctuations, are compared with analytical predictions. In order to emphasize the effects of fluctuations in these approximations, we also compare our results with dynamics governed by the Gross Pitaevskii equation. We study the dynamics of several observables, including the density and single-particle and density-density correlation functions, with particular focus on experimentally relevant quantities. [Preview Abstract] |
Tuesday, March 22, 2011 1:27PM - 1:39PM |
J45.00010: Exploring topological phases with quantum walks Takuya Kitagawa, Mark Rudner, Erez Berg, Eugene Demler The quantum walk was originally proposed as a quantum mechanical analogue of the classical random walk, and has since become a powerful tool in quantum information science. In this talk, we show that the dynamical protocols called discrete time quantum walks provide a versatile platform for studying topological phases, which are currently the subject of intense theoretical and experimental investigation. In particular, we demonstrate that recent experimental realizations of quantum walks simulate a non-trivial one dimensional topological phase. With simple modifications, the quantum walk can be engineered to realize all of the topological phases which have been classified in one and two dimensions. We further discuss the existence of robust edge modes at phase boundaries, which provide experimental signatures for the non-trivial topological character of the system. Reference: T.Kitagawa, M.Ruder, E.Berg, and E. Demler, Phys. Rev. A 82, 033429 (2010) [Preview Abstract] |
Tuesday, March 22, 2011 1:39PM - 1:51PM |
J45.00011: Universal energy distribution in thermally isolated driven systems Luca D'Alessio, Guy Bunin, Anatoli Polkovnikov, Yariv Kafri The evolution of the energy distribution of a thermally isolated and repeatedly driven system is studied. A general formalism to calculate the width of the energy distribution is derived and the result is compared with the thermal width. This comparison allow us to identify two regimes: quasi-thermal and run-away. In the quasi-thermal regime the width on the energy distribution of the driven system is proportional to the thermal width with a protocol-dependent universal coefficient. In the run-away regime the width of the energy distribution is an universal function of the energy with an exponent different from the thermal case. A simple formulation in terms of entropy production allow us to distinguish these two regimes. Examples and application to both classical and quantum system (mainly cold atoms) are presented. [Preview Abstract] |
Tuesday, March 22, 2011 1:51PM - 2:03PM |
J45.00012: Ramping through Superfluid-to-Mott transition in the Bose-Hubbard Model Bernhard Wunsch, David Pekker, Takuya Kitagawa, Efstratios Manousakis, Eugene Demler We discuss equilibrium and dynamic properties of cold bosonic atoms in optical lattices which can be described by the Bose-Hubbard Model. Motivated by recent experiments we study local density fluctuations and their correlations both in equilibrium and for a ramp from the superfluid to the Mott regime. We compare mean-field Gutzwiller approach with exact diagonalization studies and analyze the effect of a trapping potential. In order to describe fluctuations and finite temperature we include quadratic fluctuations on top of the mean field. [Preview Abstract] |
Tuesday, March 22, 2011 2:03PM - 2:15PM |
J45.00013: Dynamics of thermalisation: a Gaussian regime Sam Genway, Andrew Ho, Derek Lee We study numerically the thermalisation and temporal evolution of subsystems in a fermionic Hubbard model prepared far from equilibrium at a definite energy. Taking motivation from cold atoms in optical lattices with single-site addressability, we consider measurements on a two-site subsystem. We ask the question: how do observables on the subsystem thermalise when the total system is in a pure state? Even for very small systems near quantum degeneracy, the subsystem can reach a steady state resembling thermal equilibrium. This occurs for a non-perturbative coupling between the subsystem and the rest of the lattice where relaxation to equilibrium sharply contrasts perturbative results. To examine the extent to which this behaviour is generic for small quantum systems, we also investigate small Bose-Hubbard model systems and fermionic systems with random couplings between the subsystem and the rest of the lattice. [Preview Abstract] |
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