Bulletin of the American Physical Society
42nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 56, Number 5
Monday–Friday, June 13–17, 2011; Atlanta, Georgia
Session U1: Dissipation in Cold Atom Systems |
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Chair: Trey Porto, JQI and NIST Room: A601 |
Friday, June 17, 2011 10:30AM - 10:42AM |
U1.00001: Quantitative Studies of Vortex Decay in Finite Temperature Atomic Condensates Ashleigh Joy Allen, Carlo F. Barenghi, Nick P. Proukakis An off-centered vortex in a pure harmonically-trapped atomic condensate precesses at constant radius, as recently confirmed experimentally (D.V. Freilich \emph{et al.} Science 329, 1182 (2010).). The thermal cloud induces a frictional force on the vortex, thereby leading it to a gradual decay. Extending earlier work (B. Jackson \emph{et al.} Phys. Rev. A 79, 053615 (2009).), we perform a detailed quantitative study of the role of the dynamics of the thermal cloud on the motion of one or more vortices; we model the system by a dissipative Gross-Pitaevskii equation for the condensate, self-consistently coupled to a quantum Boltzmann equation for the thermal modes (Zaremba-Nikuni-Griffin formalism). [Preview Abstract] |
Friday, June 17, 2011 10:42AM - 10:54AM |
U1.00002: Dynamics of relaxation and the equilibrium state in an incompletely-chaotic quantum system Vladimir Yurovsky, Abraham Ben-Reuven, Maxim Olshanii An incompletely-chaotic system, with a perturbation of the integrable part that does not obey selection rules, relaxes to an equilibrium state that lies between the initial state and thermal equilibrium [1]. This behavior, which is controlled by a universal parameter, is confirmed for a system of two atoms in a circular transversally-harmonic waveguide. We analyze here the dynamics of expectation values of generic observables and their fluctuations in the long-time limit with an application to this model. The relaxation demonstrates a non-exponential behavior and its rate depends on the initial-state energy. The fluctuation amplitude decreases with increase of the initial state width.\\[4pt] [1] V. A. Yurovsky and M. Olshanii, Phys. Rev. Lett. 106, 025303 (2011) [Preview Abstract] |
Friday, June 17, 2011 10:54AM - 11:06AM |
U1.00003: Quantum Quenches in a Strongly Correlated Optical Lattice David Chen, Cecilia Borries, Matthew White, Brian DeMarco We study the excitations generated upon quenching a Mott-insulator into the superfluid regime for $^{87}$Rb atoms confined in a 3D optical lattice. The lattice is ramped-down slowly compared to U/h, such that a condensate is always reformed after the quench. Using time-of-flight imaging, we observe that the degree of excitation is proportional to the fraction of atoms crossing the phase boundary, suggesting that defect generation occurs in a quantum analog to the Kibble-Zurek mechanism. We find that the degree of excitation and the heat produced by the quench both scale universally with the quenching time $\tau_Q$ as $\tau_Q^{-1/3}$. [Preview Abstract] |
Friday, June 17, 2011 11:06AM - 11:18AM |
U1.00004: Non-equilibrium dynamics around integrability in a one-dimensional two-component Bose gas Nicolaas van Druten, Philipp Wicke, Shannon Whitlock We investigate a one-dimensional two-component Bose gas near the point of state-independent interactions. At this specific point the system is integrable, in the sense that exact (thermodynamic) Bethe Ansatz solutions can be applied locally. In the experiments, we employ an atom chip and the magnetically trappable clock states in $^{87}$Rb. State-dependent potentials are generated by using the polarization dependence of radio-frequency dressing. We show that this allows us to continuously and dynamically tune both the local interactions and the global trapping potential. The experimentally accessible range in interactions includes the region around the integrability point. We study the spin motion that follows upon a sudden change in the system, a quantum quench. When starting from a low-temperature, quantum-degenerate gas in the weakly interacting regime, good agreement with a Gross-Pitaevskii description is found. The experiment allows exploring regimes that go beyond such a description and opens up a novel route to the study of the relation between non-equilibrium dynamics, thermalization and the making and breaking of integrability in quantum many-body physics. [Preview Abstract] |
Friday, June 17, 2011 11:18AM - 11:30AM |
U1.00005: Dynamics of a quantum quench in an ultracold atomic BCS superfluid Bogdan Damski, Chih-Chun Chien We study dynamics of an ultracold atomic BCS superfluid driven toward 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 nonequilibrium 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 nonequilibrium where it is inversely proportional to the nonequilibrium gap, and strongly nonequilibrium where it decouples from both equilibrium and nonequilibrium gap. Using the Kibble-Zurek formalism, we derive scaling laws relating the non-equilibrium gap and the Cooper pair size to the quench rate. These results agree with numerical simulations. Our work should stimulate future experimental characterization of nonequilibrium ultracold atomic BCS superfluids. This work in published by C.C. Chien and B. Damski in Phys. Rev. A 82, 063616 (2010). [Preview Abstract] |
Friday, June 17, 2011 11:30AM - 11:42AM |
U1.00006: Solitons as the early stage of quasicondensate formation during evaporative cooling Piotr Deuar, Emilia Witkowska, Mariusz Gajda, Kazimierz Rzazewski The evaporative cooling dynamics of trapped one-dimensional Bose-Einstein condensates was simulated using the classical fields method. BECs and quasicondensates were obtained in the final equilibrium state, and we were able to track the onset of condensation. It was confirmed that solitons are created during the evaporation process by the Kibble-Zurek mechanism, but eventually dissipate during thermalisation. This bridges the gap between the phase defect picture of the Kibble-Zurek mechanism and the long-wavelength phase fluctuations picture in the thermal state. Interestingly, a signature of the initial defects remains in the final equilibrium state: the phase coherence length is approximately conserved during soltion dissipation. [Preview Abstract] |
Friday, June 17, 2011 11:42AM - 11:54AM |
U1.00007: Onset of thermalization in a 1D Bose gas Jean-Felix Riou, Aaron W. Reinhard, Laura Adams, David S. Weiss There has been considerable theoretical debate about how nearly integrable many-body quantum systems approach thermal equilibrium. Experiments on one dimensional Bose gases in optical lattices may shed light on this issue. We have studied the time evolution of momentum distributions of Rb clouds initially prepared in ``quantum Newton's cradle'' states [T. Kinoshita, T. Wenger and David S. Weiss, ``A quantum Newton's Cradle,'' Nature 440, 900 (2006)]. The measured evolution rates are found to depend on density and lattice depth. In order to isolate the part of the approach to equilibrium due to atom-atom interactions, it has been necessary to quantify, experimentally and theoretically, the contributions of various heating and loss processes to these rates. [Preview Abstract] |
Friday, June 17, 2011 11:54AM - 12:06PM |
U1.00008: Persistent currents from the decay of quantum turbulence: signatures of an inverse energy cascade in Bose-Einstein condensates Brian P. Anderson, Tyler W. Neely, E. Carlo Samson, Ewan M. Wright, Sam J. Rooney, Ashton S. Bradley, Matthew J. Davis, Kody J. H. Law, Ricardo Carretero-Gonzalez, Panayotis G. Kevrekidis We report the formation of persistent currents from the decay of turbulence in Bose- Einstein condensates (BECs). In our experiments, a BEC is pierced with a blue-detuned laser beam. By moving the trap center relative to the beam's position, vortices are stirred into the BEC, creating a quantum turbulent state. At finite temperatures, the turbulent state can decay to a persistent current about the blue-detuned laser beam that can last for up to 50 seconds; winding numbers up to 8 have been observed. Our experimental observations correspond well with numerical simulations of the non-equilibrium dynamics and calculations of vortex pinning by a laser beam. We interpret our results as evidence for an inverse energy cascade in dilute-gas BECs. [Preview Abstract] |
Friday, June 17, 2011 12:06PM - 12:18PM |
U1.00009: Macroscopic Quantum Tunneling of Solitons in Bose-Einstein Condensates Joseph A. Glick, Lincoln D. Carr We study the macroscopic quantum tunneling of ultracold bosons in one-dimensional optical lattices. A bright matter-wave soliton behind a potential barrier is allowed to tunnel out of confinement by tuning the barrier width and the attractive particle-particle interactions. We predict the escape time for the soliton, that is, when the norm remaining behind the barrier drops to 1/e, modeling how the interaction strength, the system size, and the barrier dimensions affect the escape time. We preform quasi-exact simulations of the quantum many-body entangled dynamics with Time-Evolving Block Decimation (TEBD), a matrix product state numerical method. Independently, we check our results near the weakly interacting limit with mean-field theory. Our findings show the regimes in which mean-field theory is widely inadequate, and the appreciable differences between a mean-field and a full quantum many-body approach. We then use TEBD to model the dynamics far beyond the mean-field limit. We calculate the entropy of entanglement between the soliton body behind the barrier and the escaped soliton tail past the barrier over time. We use density-density correlation functions to examine how particles in different regions of the system (behind, under, or past the barrier) are entangled to one another. [Preview Abstract] |
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