Bulletin of the American Physical Society
40th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 54, Number 7
Tuesday–Saturday, May 19–23, 2009; Charlottesville, Virginia
Session J3: Dynamics and Out of Equilibrium Phenomena in Cold Atoms |
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Chair: Chandra Raman, Georgia Institute of Technology Room: Gilmer Hall 190 |
Thursday, May 21, 2009 8:00AM - 8:12AM |
J3.00001: Light scattering dynamics on the $F=1 \to F'=0$ transition in a high-density ultracold atomic gas of $^{87}$Rb S. Balik, A. Win, I.M. Sokolov, D.V. Kupriyanov, M.D. Havey Experimental study of light scattering dynamics for atomic densities near the so-called Ioffe Regel boundary is crucial in exploration of current areas of research such as light localization and atomic physics based random lasers. We report experimental results on light scattering studies in an ultracold and high density (5 x 10$^{13}$ atoms/cm$^{3}$) gas of $^{87}$Rb atoms. Spectral and probe intensity dependent measurements of the time-evolution of light scattered on the $F=1 \to F'=0$ transition show strong Zeeman optical pumping effects that causes relatively short lived transients and dynamical evolution from high to low optical depths, despite the initally high atomic density. Comprehensive experimental results ranging over an order of magnitude in atomic density, probe laser intensity and about $\pm$ 20 MHz detuning from atomic resonance will be reported and discussed. [Preview Abstract] |
Thursday, May 21, 2009 8:12AM - 8:24AM |
J3.00002: Non-equilibrium behavior of the formation of a Bose-Einstein condensate in a disordered one-dimensional optical lattice Emily Edwards, Matthew Beeler, Tao Hong, Steven Rolston Equilibrium many-body dynamics is well described by statistical thermodynamics, but non-equilibrium systems are more common in nature and also much more difficult to study. A familiar example of a system driven by non-equilibrium thermodynamics is a laser. Some other notable laboratory examples are experiments in superfluid $^{3}$He, liquid crystals, and superconducting films. There are fundamental questions, such as how a closed system reaches equilibrium, global or local. Does the final state retain memory of the initial state? The control and measurement tools available in ultra-cold atom experiments make for a promising laboratory to study these quantum dynamics. We will report on the progress of experiments investigating the many-body dynamics of condensation formation in a single period and disordered one-dimensional optical lattice. This work is partially supported by the ARO. [Preview Abstract] |
Thursday, May 21, 2009 8:24AM - 8:36AM |
J3.00003: Anomalous spin segregation in a weakly interacting two component Fermi gas Stefan Natu, Erich Mueller We explain the spin segregation seen at Duke in a two-component gas of 6Li (Ref.[1]) as a mean-field effect describable via a collisionless Boltzmann equation. As seen in experiments, we find that slight differences in the trapping potentials in the two spin states drive small spin currents. Hartree-Fock type interactions convert these currents into a redistribution of populations in energy space, and consequently a long lived spin texture develops. We explore the interaction strength dependence of these dynamics, finding close agreement with experiment. [1] X.Du, L.Luo, B.Clancy, and J.E. Thomas, Phys. Rev. Lett. 101 150401 (2008). [Preview Abstract] |
Thursday, May 21, 2009 8:36AM - 8:48AM |
J3.00004: Controlling the Ratchet Effect for Cold Atoms Arjendu Pattanayak, Anatole Kenfack, Jiang Bin Gong Low-order quantum resonances manifested by directed currents have been realized with cold atoms. Here we show that by increasing the strength of an experimentally achievable delta-kicking ratchet potential, quantum resonances of a very high order may naturally emerge and can induce larger ratchet currents than low-order resonances, with the underlying classical limit being fully chaotic. The results offer a means of controlling quantum transport of cold atoms [Preview Abstract] |
Thursday, May 21, 2009 8:48AM - 9:00AM |
J3.00005: Supercurrent decay in one-dimensional Bose gases in a ring optical lattice Ippei Danshita, Anatoli Polkovnikov Applying the time-evolving block decimation method to the Bose-Hubbard model with a periodic boundary condition, we study the decay dynamics of supercurrents in one-dimensional lattice bosons. We show that while a supercurrent persists when the ratio of the onsite interacton U to the hopping J is sufficiently small, increasing U/J enhances quantum fluctuations and causes the decay of the supercurrent. In the case of commensurate filling, we find a coherent oscillation between certain momenta p and -p resulting from the decay instead of the relaxation to a zero momentum state. We also find that the double-phase slip, in which the winding number of the supercurrent suddenly changes from 1 to -1, occurs associated with this oscillation. [Preview Abstract] |
Thursday, May 21, 2009 9:00AM - 9:12AM |
J3.00006: A supercritical superfluid Or: Seeing vortices unbind Ludwig Mathey, Anatoli Polkovnikov We study the dynamics of the relative phase of a bilayer of two-dimensional superfluids after the two superfluids have been decoupled, using truncated Wigner approximation. We find that on short time scales the relative phase shows ``light cone'' like dynamics, and creates a metastable quasi-superfluid state. On longer time scales this state relaxes to a disordered state due to dynamical vortex unbinding. We note that these results are directly measurable in interference experiments. [Preview Abstract] |
Thursday, May 21, 2009 9:12AM - 9:24AM |
J3.00007: Relaxation dynamics in quasi one-dimensional cold gases Dominik Muth, Michael Fleischhauer Due to the fast developement of experimental techniques it now becomes possible to study the dynamics of interacting ultra-cold quantum gases. Furthermore deep optical lattices or atom chips provide access to the quasi one-dimensional regime. While one-dimensional quantum gases with local interactions are integrable even for finite interaction strength, experiments necessarily contain small distortions e.g. due to transversal excitations in the confinement or coupling between different one-dimensional cells. These destroy integrability and make the system relax into a thermal state, given by the usual canonical ensemble. We investigate theoretically the connection between the strength of the distortions and the rate of thermalization. The analytical results are complemented with numerical simulations using the Time Evolving Block Decimation algorithm, a powerful tool for one-dimensional quantum systems, that allows us to go beyond the regime covered by perturbation theory. [Preview Abstract] |
Thursday, May 21, 2009 9:24AM - 9:36AM |
J3.00008: On the microscopic theoretical approach of Spontaneous Symmetry Breaking in parametrically driven Cold atomic system Junhyun Lee, Yonghee Kim, Myoung-Sun Heo, Wonho Jhe, Mark Dykman Although Spontaneous Symmetry Breaking (SSB) of atom clouds in parametrically driven Magneto-Optical Trap (MOT) has been reported, the precise mechanism of SSB in atomic level is yet fully recognized. In this presentation, therefore, we explore the microscopic theory underlying the SSB phenomenon. Starting with the well-known process of change of variables followed by the method of averaging, we newly include the interaction force, which is of the form of a step function. Using this model, we investigate how the transition rate of an atom between the two attractors changes in the presence of a second fixed atom. We generalize this result by adding more atoms and allowing mutual transitions. Based on these observations we attempt to predict the critical number required for SSB. We also show that this result is well compatible with the acknowledged relation between transition rate and activation energy. Finally, the theoretical approach is compared with the experimental results. [Preview Abstract] |
Thursday, May 21, 2009 9:36AM - 9:48AM |
J3.00009: Time-symmetry breaking for modulated cold atoms as a realization of meanfield critical behavior Myoung-Sun Heo, Yonghee Kim, Geol Moon, Mark Dykman, Wonho Jhe Cold atoms have been widely used for the studies of many-body physics and critical phenomena in particular. However, most of the work on critical phenomena focused on systems effectively close to thermal equilibrium. Here we show that cold atoms make it possible to reveal and explore, qualitatively and quantitatively, critical behavior far from thermal equilibrium. We study periodically modulated atomic cloud in a magneto-optical trap which is invariant under the discrete time-translation by the modulation period $\tau _F $. Once the number of atoms reaches a critical value, they preferably occupy one of the two parametrically excited vibrational states, which has the time-translation symmetry of $2\tau _F $. We find that, even though the states are explicitly time-dependent, the system displays an ideal mean-field critical dynamics. It is seen in the critical exponents of the order parameter and the static susceptibility, as well as in the dynamic response. The cold atoms dynamics is determined by the interplay of the interaction and fluctuations; it is quantitatively described. The results demonstrate that fluctuations in interacting systems far from equilibrium lead to new types of collective behavior and provide a qualitative and quantitative insight into an important type of such behavior. [Preview Abstract] |
Thursday, May 21, 2009 9:48AM - 10:00AM |
J3.00010: Effects of quantum fluctuations on the pulsating instability of a BEC in an optical lattice Uttam Shrestha, Juha Javanainen, Janne Ruostekoski We study the effects of quantum fluctuations on the dynamics of a classically unstable weakly interacting Bose-Einstein condensate in an optical lattice. We incorporate the quantum effects approximately within the truncated Wigner approximation. We observe that the pulsating dynamical instability, in which atoms nearly periodically collect together and subsequently disperse back to the initial homogeneous state, survives for a single realizations that represents a typical experimental outcome. However, ensemble averages of various physical properties manifest the effect of quantum fluctuations. The quantum effects become more prominent when the effective interaction strength is increased. [Preview Abstract] |
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