Bulletin of the American Physical Society
43rd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 57, Number 5
Monday–Friday, June 4–8, 2012; Orange County, California
Session P4: Non-equilibrium Dynamics in Ultracold Systems |
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Chair: Marcos Rigol, Georgetown University Room: Garden 1-2 |
Thursday, June 7, 2012 2:00PM - 2:12PM |
P4.00001: Acoustic analog of the dynamical Casimir effect in Bose-Einstein Condensates Jean-Christophe Jaskula, Guthrie Partridge, Marie Bonneau, Josselin Ruaudel, Denis Boiron, Christopher Westbrook Although we often picture the quantum vacuum as containing virtual quanta whose observable effects are only indirect, it is a remarkable prediction of quantum field theory that the vacuum can generate real particles when boundary conditions are suddenly changed. Thus the ``dynamical Casimir effect'' or the 'Hawking radiation' result in the spontaneous generation of photon pairs in an empty cavity whose boundaries are rapidly moving or at the horizon of a black hole. In 1981, W. Unruh pointed out an acoustic analog to Hawking radiation. Further work on this idea has developed into an entire field, and recently a stimulated analog to Hawking radiation has been observed using surface waves on water. Bose Einstein condensates are attractive candidates in which to study such analog models because their low temperatures promise to reveal quantum effects. We present the realization of an acoustic analog to the dynamical Casimir effect by modulating the confinement of a Bose-Einstein condensate. We show that correlated pairs of Bogoliubov quanta, both phonon-like and particle-like, are excited by this modulation, in a process that formally resembles parametric down conversion. [Preview Abstract] |
Thursday, June 7, 2012 2:12PM - 2:24PM |
P4.00002: Integrability versus Thermalizability in Isolated Quantum Systems Maxim Olshanii The purpose of this presentation is to propose a rigorous measure of the degree of quantum thermalizability, consistent with the expected empirical manifestations of it. As a practical application of this measure, we devise a unified recipe for choosing an optimal set of conserved quantities to govern the after-relaxation values of observables, in both integrable quantum systems and in quantum systems in between integrable and thermalizable. [Preview Abstract] |
Thursday, June 7, 2012 2:24PM - 2:36PM |
P4.00003: Relaxation Dynamics and Pre-thermalization in an Isolated Quantum System Maximilian Kuhnert, Michael Gring, Tim Langen, Takuya Kitagawa, Bernhard Rauer, Igor Mazets, David A. Smith, Eugene Demler, Joerg Schmiedmayer Understanding relaxation processes is an important unsolved problem in many areas of physics. This fact is exacerbated by the scarcity of experimental tools for characterizing complex transient states. We employ measurements of full quantum mechanical probability distributions of matter-wave interference to study the relaxation dynamics of a coherently split one-dimensional Bose gas and obtain unprecedented information about the dynamical states of the system. Following an initial rapid evolution, the full distributions reveal the approach towards a thermal-like steady state which exhibits an effective temperature eight times lower than the initial equilibrium temperature of the system as well as a strong memory of the initial state prepared by the splitting process. We associate this thermal-like state with pre-thermalization. [Preview Abstract] |
Thursday, June 7, 2012 2:36PM - 2:48PM |
P4.00004: Non-equilibrium dynamics of a 1D Bose gas in a flat optical lattice potential Aaron Reinhard, Laura Zundel, Jean-Felix Riou, Juan Carrasquilla, Marcos Rigol, David Weiss We study the dynamics of a bundle of expanding 1D Bose gases in a nearly flat 1D optical lattice potential in the intermediate coupling regime, which presents a challenge to theory. We observe the time-evolving spatial and quasimomentum distributions at a range of 1D atom densities and 1D lattice depths. Since it is difficult to exactly model these non-equilibrium dynamics, we take a first step towards theoretical understanding by comparing our measurements to the results of a Gutzwiller mean-field model. [Preview Abstract] |
Thursday, June 7, 2012 2:48PM - 3:00PM |
P4.00005: Quantum flutter of supersonic particles in one-dimensional quantum liquids Charles Mathy, Mikhail Zvonarev, Eugene Demler We study the dynamics of an impurity injected at a supersonic velocity into a 1D gas of hardcore bosons, or faster than the Fermi velocity in a fully polarized Fermi gas. We find that at long times the momentum of the impurity does not decay to zero, and demonstrate that the system exhibits a new type of coherent oscillation in which the impurity vibrates with respect to its correlation hole. [Preview Abstract] |
Thursday, June 7, 2012 3:00PM - 3:12PM |
P4.00006: Asymptotic limit of momentum distribution functions in the sudden expansion a spin-imbalanced Fermi gas in one dimension Stephan Langer, Carlos Bolech, Ian McCulloch, Fabian Heidrich-Meisner, Guilano Orso, Marcos Rigol We study the sudden expansion of a spin-imbalanced Fermi gas in an optical lattice after quenching the trapping potential to zero, described by the attractive Hubbard model. Using time-dependent density matrix renormalization group simulations we demonstrate that the momentum distribution functions (MDFs) of majority and minority fermions become stationary after sufficiently long simulation times. Our main result is that the asymptotic form of the MDFs is fully determined by the integrals of motion of this integrable quantum systems, namely the rapidities from the Bethe ansatz solution, which we show by a direct comparison of DMRG and Bethe ansatz predictions. We discuss the relevance of our results for the observation of Fulde-Ferrell-Larkin-Ovchinnikov correlations in one-dimensional systems, related to recent experiments from Rice University (Liao et al. Nature 467, 567 (2010)). [Preview Abstract] |
Thursday, June 7, 2012 3:12PM - 3:24PM |
P4.00007: Quantum Quench of a p-Wave Fermi Gas across the Quantum Phase Transition Sukjin Yoon, Gentaro Watanabe We investigate the non-equilibrium dynamics following a quantum quench across the quantum phase transition in a p-wave superfluid Fermi gas at zero temperature. This case is distinct from the s-wave case where the change from the BCS to BEC regime is just a crossover. The quench dynamics of a polar state as well as an axial state of the p-wave superfluid Fermi gas are studied. The time evolutions of the order parameter are obtained within a mean field approach and compared with the s-wave case. [Preview Abstract] |
Thursday, June 7, 2012 3:24PM - 3:36PM |
P4.00008: A new theoretical method to describe nonequilibrium cold atoms in optical lattices Karlis Mikelsons, Jim Freericks, H.R. Krishnamurthy We use perturbation theory in the hopping (strong-coupling expansion) to describe the nonequilibrium dynamics of strongly correlated fermions. Our expansion is a self-consistent expansion for the self-energy which goes beyond the RPA and allows for damping and relaxation effects. We apply this method to solve the homogeneous Fermi - Hubbard model driven by an external field. We investigate the damping of Bloch oscillations (for a uniform dc field) and show results for the current, the nonequilibrium density of states and the momentum distribution. We carefully benchmark the technique using the exact sum rules to determine its accuracy and we discuss regions of parameter space where the method no longer converges. This technique is quite competitive with other methods (such as DMFT) in the regions where it converges. [Preview Abstract] |
Thursday, June 7, 2012 3:36PM - 3:48PM |
P4.00009: No indirect increase in precision of energy measurements from nonlinearity in a two-well trap Han Chen, Juha Javanainen We study a two-well trap containing a Bose-Einstein condensate as a prototype for interferometric measurements of the energy difference of the atoms between the two sides of the trap. The measurement relies on a coupling to atom numbers, which implies the Heisenberg limit of precision. However, it is known that a nonlinear scheme, a measurement coupling proportional to a power of atom number higher than one, may defeat the Heisenberg limit. Here we ask if the nonlinear atom-atom interaction that couples to the dynamics of the system as a whole could indirectly increase the precision of energy measurements. Our numerical analysis indicates that it is not the case. [Preview Abstract] |
Thursday, June 7, 2012 3:48PM - 4:00PM |
P4.00010: Pattern formation of quantum jumps with Rydberg atoms Tony Lee, Michael Cross We study the nonequilibrium dynamics of quantum jumps in a one-dimensional chain of atoms. Each atom is driven on a strong transition to a short-lived state and on a weak transition to a metastable state. We choose the metastable state to be a Rydberg state so that when an atom jumps to the Rydberg state, it inhibits or enhances jumps in the neighboring atoms. This leads to rich spatiotemporal dynamics that are visible in the fluorescence of the strong transition. It also allows one to dissipatively prepare Rydberg crystals. [Preview Abstract] |
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