Bulletin of the American Physical Society
39th Annual Meeting of the APS Division of Atomic, Molecular, and Optical Physics
Volume 53, Number 7
Tuesday–Saturday, May 27–31, 2008; State College, Pennsylvania
Session J4: Dynamic and Out-of-Equilibrium Phenomena in Cold Atoms |
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Chair: Dan Gauthier, Duke University Room: Nittany Lion Inn Ballroom AB |
Thursday, May 29, 2008 11:00AM - 11:12AM |
J4.00001: Thermalization and its mechanism for generic quantum isolated systems Maxim Olshanii, Vanja Dunjko, Marcos Rigol Time dynamics of isolated many-body quantum systems has long been an elusive subject, perhaps most urgently needed in the foundations of quantum statistical mechanics. In generic systems, one expects the nonequilibrium dynamics to lead to thermalization: a relaxation to states where the values of macroscopic quantities are stationary, universal with respect to widely differing initial conditions, and predictable through the time-tested recipe of statistical mechanics. The relaxation mechanism is not obvious, however; dynamical chaos cannot play the key role as it does in classical systems since quantum evolution is linear. Here we demonstrate\footnote{M.\ Rigol, V.\ Dunjko, and M.\ Olshanii, to appear in Nature (2008)}, using the results of an {\it ab initio} numerical experiment with $5$ hard-core bosons moving in a $5\times5$ lattice, that in quantum systems thermalization happens not in course of time evolution but instead at the level of individual eigenstates, as first proposed by Deutsch\footnote{J.\ M.\ Deutsch, Phys.Rev.\ A 43, 2046 (1991)} and Srednicki\footnote{M.\ Srednicki, Phys.\ Rev.\ E 50, 888 (1994)}. [Preview Abstract] |
Thursday, May 29, 2008 11:12AM - 11:24AM |
J4.00002: Chaos Criterion in Bose-Hubbard Model Amy Cassidy, Vanja Dunjko, Maxim Olshanii The goal of this work is to determine the criterion for chaos in the one-dimensional mean-field Bose-Hubbard model. We investigate the time evolution of a system with a few low-energy momentum modes excited initially. A threshold for chaos is identified from calculations of the largest Lyapunov exponent, which is compared with the predictions of the Chrikov criterion of overlapping resonances. Additionally, the results are compared with a closely related fully integrable model. [Preview Abstract] |
Thursday, May 29, 2008 11:24AM - 11:36AM |
J4.00003: Controlled transition to complete multiparticle quantum dynamics from classical field simulations of interacting bosons Piotr Deuar The classical field (or truncated Wigner) and the positive P methods are in use to simulate non-equilibrium quantum dynamics of large interacting bosonic systems, such as BECs, beyond the mean-field approximation. However, the classical field method is inherently an approximation that discards some processes. Although it can often be argued that the discarded evolution is relatively small, so are many quantities of interest beyond the mean-field description. Their accuracy in the simulation often remains unknown, limiting its use. The positive P method, on the other hand, while giving the complete quantum dynamics, gives useful precision only for a limited evolution time. Here, a technique is presented that allows the gradual and controlled introduction of the non-classical-field parts of the evolution, interpolating from the classical field to the complete quantum dynamics of the positive P. This allows one to assess the accuracy of the long-time classical field calculations quantitatively and provide confidence, if warranted. It can play a similar role here to the controlled addition of increasing state complexity in DMRG methods. [Preview Abstract] |
Thursday, May 29, 2008 11:36AM - 11:48AM |
J4.00004: Resonances of a quanrum delta kicked accelerator Vijayashankar Ramareddy, I. Talukdar, Gil Summy, G. Behinaein, P. Ahmadi A quantum d-kicked accelerator exhibits the phenomenon of resonance whenever the period of kicking is a rational fraction of the half-Talbot time similar to a quantum d-kicked rotor. The signatures of these resonances are the existence of quantum accelerator modes. We observed resonances for the periods of 1/2, 2/3, and 1/3 of the half-Talbot time. A model based on the rephasing of the momentum states constituting the accelerator modes has been successfully used to predict the behavior. [Preview Abstract] |
Thursday, May 29, 2008 11:48AM - 12:00PM |
J4.00005: Quantum resonance ratchet using a delta kicked rotor Vijayashankar Ramareddy, Itzhack Dana, Ishan Talukdar, Gil Summy Quantum-resonance ratchets associated with the periodically kicked particle are experimentally realized [1]. This is achieved by using a Bose-Einstein condensate exposed to a pulsed standing light wave and prepared in an initial state differing from the usual plane wave. Both the standing-wave potential and the initial state have a point symmetry around some center and the ratchet arises from the non-coincidence of the two centers. The dependence of the directed quantum transport on the quasimomentum is studied. A theoretical analysis is used to explain the experimental results. [1] I. Dana et. al., Phys. Rev. Lett. 100, 024103 (2008). [Preview Abstract] |
Thursday, May 29, 2008 12:00PM - 12:12PM |
J4.00006: Two-body transients in coupled atomic-molecular Bose-Einstein Condentates Eite Tiesinga, Pascal Naidon, Paul Julienne The conversion of atom pairs into molecules, using either Feshbach resonances or photoassociation can serve as a tool to probe the many-body properties of ultracold gases. In particular, photoassociation, the process of associating atoms with a resonant laser light, was recently used to observe pair correlation in a 1D Bose gas and in the BEC-BCS crossover. Conversely, it can be used to reach new collective regimes. Theories have suggested the coherent conversion of an atomic Bose-Einstein condensate into a condensate of molecules, the possibility of macroscopic superposition, and production of correlated atom pairs (or rogue dissociation) at high laser intensity. Several experiments have made the first steps in these directions. We discuss the dynamics of an atomic Bose-Einstein condensate when pairs of atoms are converted into molecules by photoassociation. Three regimes are found and it is shown that they can be understood on the basis of time-dependent two-body theory. In particular, the rogue dissociation regime, which has a density-dependent limit on the photoassociation rate, is identified with a transient in the two-atom dynamics exhibiting universal properties. We illustrate how these regimes can be explored by photoassociating condensates of alkaline-earth atoms. [Preview Abstract] |
Thursday, May 29, 2008 12:12PM - 12:24PM |
J4.00007: Stochastic phenomena in parametrically driven magneto-optically trapped atomic system Yonghee Kim, Myoung-Sun Heo, Wonho Jhe, Heung-Ryoul Noh Stochastic dynamics of periodically driven cold atom system was investigated. The studies focused on the phenomena between the parametrically excited period-2 states. The transition rates of single atom activated by the stochastic process were measured. When atom number increased or additional bias field applied, we observed symmetric population of period-2 states was broken. In number varying case, mean field Ising-type phase transition was observed. The other case which additional bias field exerted, hysteretic response was occurred. In addition, the transient phenomena of atomic population near the unstable state have been observed. Relevant asymptotic behavior of relaxation rate has been quantitatively measured and anomalous fluctuation qualitatively discussed. [Preview Abstract] |
Thursday, May 29, 2008 12:24PM - 12:36PM |
J4.00008: Pulsating Instability of a Bose-Einstein Condensate in an Optical Lattice Uttam Shrestha, Juha Javanainen We find numerically that in the limit of weak atom-atom interactions a Bose-Einstein condensate in an optical lattice prepared in an unstable steady state may develop a pulsating dynamical instability in which the atoms periodically or quasiperiodically collect into a pulse and then disperse back to the unstable initial state. We obtain the parameter regime for the pulsations using Bogoliubov type analysis. A qualitative explanation of the quasiperiodic behavior is given by drawing from an analogy with a double-well system. Simple arguments give both a qualitative and a quantitative description of the pulsations. [Preview Abstract] |
Thursday, May 29, 2008 12:36PM - 12:48PM |
J4.00009: Microwave Controlled Transport and Collisions of Cs Atoms in an Optical Lattice Jae Hoon Lee, Worawarong Rakreungdet, Enrique Montano, Brian Mischuck, Ivan Deutsch, Poul Jessen Quantum information processing with atomic qubits in optical lattices requires two-qubit entangling operations that can be implemented by e.g. controlled pairwise collisions. As a step in this direction we are working on an experiment that uses microwave transitions to control the motion of Cs atoms between the sites of an anti-ferromagnetic lattice. In Cs the relevant ground state scattering length is large enough for a pair of atoms at neighboring spin-up/down sites to be bound together in a long range molecular state whose energy can be shifted by a large amount relative to isolated, non-interacting atoms. In principle this shift can be used as the basis for a quantum phase gate. We are currently attempting to observe distinct lines in the microwave spectrum corresponding to excitation of this molecular state. [Preview Abstract] |
Thursday, May 29, 2008 12:48PM - 1:00PM |
J4.00010: Interaction-controlled transport of an ultracold Fermi gas Robert Jordens, Niels Strohmaier, Yosuke Takasu, Kenneth Gunter, Michael Kohl, Henning Moritz, Tilman Esslinger We explore the transport properties of an interacting Fermi gas in a three-dimensional optical lattice. In analogy to the characterization of transport behavior in condensed matter systems through conductivity measurements, we study the atom cloud's center of mass motion after a sudden displacement of the trap minimum. Different interaction strengths and lattice fillings are shown to have a characteristic influence on the dynamics. With increasingly strong attractive interactions the weakly damped oscillation, observed for the non-interacting case, turns into a slow drift: local pairs with a reduced tunneling rate are formed for strong inter-atomic attraction. Application of this technique in other interaction regimes, lattice depths and fillings in the Fermi-Hubbard model may provide a tool for the identification of quantum phases such as the fermionic Mott-insulator. Experimental results on repulsively interacting Fermi gases will be presented. [Preview Abstract] |
Thursday, May 29, 2008 1:00PM - 1:12PM |
J4.00011: Damped motion of one-dimensional Bose gases in an optical lattice Ippei Danshita, Charles W. Clark We study strongly correlated one-dimensional Bose gases in a combined harmonic and optical lattice potential. Using the time-evolving block decimation method, we simulate the dynamics of the Bose gases subject to a sudden displacement of the confining potential as was done in a recent experiment [C. D. Fertig et al., Phys. Rev. Lett. 94, 120403 (2005)]. We find that damping of the dipole oscillations of the Bose gases is significant even for shallow lattices and that the Bose gases become almost immobile as the lattice depth increases. These results are consistent with the experiments. We also find prominent growth of the noncondensate fraction of the Bose gases associated with the damping, which means that the damped motion is due to the breakdown of superfluidity of the Bose gases. [Preview Abstract] |
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