Bulletin of the American Physical Society
41st Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 55, Number 5
Tuesday–Saturday, May 25–29, 2010; Houston, Texas
Session W4: Dynamics with Ultracold Atomic Gases II 
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Chair: Ian Spielman, National Institute of Standards and Technology Room: Regency Ballroom 
Saturday, May 29, 2010 8:00AM  8:12AM 
W4.00001: Thermometry and Dynamics of TwoComponent Ultracold Gases in Optical Lattices Hirokazu Miyake, Patrick Medley, David Weld, David Pritchard, Wolfgang Ketterle Twocomponent mixtures of ultracold atoms in optical lattices are expected to exhibit novel manybody quantum phases at very low temperatures. We have used such a system to realize a new type of latticebased thermometry with $^{87}$Rb atoms, which we call spin gradient thermometry. We present results of this thermometry technique, which include measurement of temperatures as low as 1 nK in the Mott insulating state. We also present results of a study of nonequilibrium spin dynamics in this system. Understanding the time scale of relaxation towards equilibrium is crucial to the realization of quantum magnetism. Furthermore, controlling spin relaxation processes may enable realization of a new cooling scheme analogous to adiabatic demagnetization cooling. [Preview Abstract] 

W4.00002: ABSTRACT WITHDRAWN 
Saturday, May 29, 2010 8:24AM  8:36AM 
W4.00003: Nonlinear dynamics from quantum mechanics for a BEC in a twowell potential Juha Javanainen We study theoretically a BoseEinstein condensate in a doublewell trap. With a sudden switch of the parameters the condensate is put in a state that would be an unstable equilibrium in the classical GrossPitaevskii equation description. Classically one would expect that the system recedes exponentially in time from the equilibrium, but such behavior is not possible under the unitary time evolution of quantum mechanics. We introduce a skeleton model for the detection of the numbers of condensate atoms in each potential well by light scattering. The strength of the measurement may be varied by varying the intensity of the probe light, thereby also adjusting the strength of the measurement backaction. We simulate individual runs of such an experiment using quantum trajectory methods. The distribution of the atoms between the two traps as inferred from the scattered light closely mimics the expected classical behavior provided the measurement is intrusive enough to resolve it, but not so strong that the backaction completely dominates the dynamics. [Preview Abstract] 
Saturday, May 29, 2010 8:36AM  8:48AM 
W4.00004: Dynamical instabilities of fermion superfluids in an optical lattice Arun Paramekanti, Ramachandran Ganesh, Anton Burkov We study the breakdown of superfluidity in the attractive fermion Hubbard model in the presence of a nonzero supercurrent. Using a generalized random phase approximation as well as a strong coupling pseudospin approach, we find that there is a wide range of interaction strengths and fillings at which the superflow can break down via a novel charge modulational dynamical instability. This instability is distinct from previously studied dynamical instabilities of Bose superfluids. The charge order associated with this instability can be either: (i) a commensurate checkerboard modulation driven by softening of a rotonlike mode at the Brillouin zone corner, or, (ii) an incommensurate density modulation arising from superflowinduced finite momentum pairing of fermionic Bogoliubov quasiparticles. We obtain the mean field dynamical phase diagram showing the critical flow momentum of the leading instability over a wide range of fermion densities and interaction strengths and point out experimental implications for cold atom fermion superfluids in an optical lattice. [Preview Abstract] 
Saturday, May 29, 2010 8:48AM  9:00AM 
W4.00005: Quantum dynamics of the dissociation of a molecular BEC into fermionic atoms Joel Corney, Magnus \"Ogren, Karen Kheruntsyan We numerically simulate the exact quantum manybody dynamics of bosonic dimers dissociating into fermionic atoms by applying a Gaussian phasespace representation. The accuracy for higherorder correlations is demonstrated by comparison with a standard matrix representation for small systems of $10$ molecules and $10$ atomic modes. We then give results for systems of $10^{2}10^{4}$ molecules and $10^{3}$ atomic modes, illustrating the potential capability of the phasespace representation for firstprinciples quantum dynamical simulations for fermionic systems of realistic sizes in current experiments. Moleculeatom correlations and the decoherence of the initially condensed molecules are studied as time evolves, with clear deviations from the approximate pairing meanfield theory. [Preview Abstract] 
Saturday, May 29, 2010 9:00AM  9:12AM 
W4.00006: Dynamics of fermionization for strongly interacting photons in 1D Dominik Muth, Bernd Schmidt, Michael Fleischhauer When slowlight photons are confined to one spatial dimension with strong repulsive twophoton scattering they will fermionize, i.e. they will form the analog of a LiebLiniger gas in the Tonks limit [1]. We here analyze the dynamics of this process both for repulsive and attractive elastic twophoton scattering using exact numerical methods. We observe that the local twobody correlation attains a steadystate value after a short time, which is however substantially above the groundstate value of the LiebLiniger gas but is very close to the value in a high temperature state. This can be explained as a local thermalization to a temperature corresponding to the energy input by the sudden onset of interactions. Nonlocal twoparticle correlations approach the steadystate on a longer time scale. In the case of attractive interactions, the non local correlations indicate a relaxation to a metastable steadystate, the super TonksGirardeau gas, recently seen for bosons in the experiment by Haller et al. [2]. \newline [1] D. E. Chang, V. Gritsev, G. Morigi, V. Vuletic, M. D. Lukin, and E. A. Demler, Nature Physics 4, 884 (2008) \newline [2] E. Haller, M. Gustavsson, M. J. Mark, J. G. Danzl, R. Hart, G. Pupillo, and H. C. Naegerl, Science 325, 1224 (2009) [Preview Abstract] 
Saturday, May 29, 2010 9:12AM  9:24AM 
W4.00007: Thermalization in 1d many body systems I.E. Mazets, J. Schmiedmayer We study the collisional processes that can lead to thermalization in onedimensional systems. For two body collisions excitations of transverse modes are the prerequisite for energy exchange and thermalzation. At very low temperatures excitations of transverse modes are exponentially suppressed, thermalization by two body collisions stops and the system should become intrgrable. In quantum mechanics virtual excitations of higher radial modes are possible. These virtually excited radial modes give rise to effective threebody velocitychanging collisions which lead to thermalization (Mazets et al. PRL \textbf{100}, 210403 (2008). These threebody elastic interactions are suppressed by pair wise quantum correlations when approaching the strongly correlated regime. If the relative momentum $k$ is small compared to the twobody coupling constant $c$ the threeparticle scattering state is suppressed by a factor of ($k$/$c)^{12,}$ which is proportional to the square of the threebody correlation function at zero distance (Mazets et al. PRA \textbf{79}, 061603 (2009). This suggests that in one dimensional quantum systems it is not the freezeout of two body collisions but the strong quantum correlations which ensures integrability. [Preview Abstract] 
Saturday, May 29, 2010 9:24AM  9:36AM 
W4.00008: Nearequilibrium dynamics of an atomic gas near a quantum phase transition Xibo Zhang, ChenLung Hung, Peter Scherpelz, Nathan Gemelke, Cheng Chin Atomic gases in optical lattices can establish thermodynamic equilibrium at two different length scales: locally over a few lattice sites and globally over the whole sample. While the time scales for atoms to reach local equilibrium depend on microscopic interaction and tunneling, the time scales to reach global equilibrium remain unknown. Here we study the nearequilibrium dynamics of a twodimensional (2D) atomic gas near the bosonic superfluid to Mott insulator phase transition. Starting from a cesium133 BoseEinstein condensate in a 2D potential, we ramp up an optical lattice at different rates and observe the evolution of the atomic density profile using in situ microscopy. We analyze the density redistribution and extract relevant time scales for the sample to reach equilibrium. In addition, we probe the occupation number statistics by inducing threebody loss in the sample. We discuss how the detailed establishment of equilibrium affects studies of the superfluid and Mott insulator phases. [Preview Abstract] 
Saturday, May 29, 2010 9:36AM  9:48AM 
W4.00009: Thermalization in 1D, 2D, and 3D SpinDependent Lattices David McKay, Brian DeMarco Spin and speciesdependent optical lattices have potential applications for both cooling and thermometry in experiments with strongly correlated phases. However, these schemes presume that gases experiencing drastically different potentials remain in thermal equilibrium. We will present thermalization measurements for two cotrapped species, one that is latticebound and another that is confined harmonically. We use $^{87}$Rb atoms confined in a 1064 nm dipole trap combined with a spindependent lattice; appropriate tuning of the lattice wavelength, polarization, and magnetic field direction realize a lattice with potential depth proportional to m$_F$g$_F$. The m$_F$=0 state of $^{87}$Rb therefore does not experience the lattice potential, while the m$_F$=1 state can be strongly lattice bound. Modulation of the lattice is used to preferentially heat the m$_F$=1 gas, and measurements of the subsequent return to thermal equilibrium are used to infer the thermalization rate. We will comment on the prospects for using this system for thermometry and also on technical issues such as heating and inelastic loss. [Preview Abstract] 
Saturday, May 29, 2010 9:48AM  10:00AM 
W4.00010: A Study of Nonadiabatic Effects When a 1D Optical Lattice is Turned on Rapidly T. Bergeman, H. Shim, D. Pertot, B. Gadway, D. Schneble Nonadiabatic effects that can occur when Bose condensates are subject to a rapidly rising optical lattice have attracted much interested in regard to experiments such as [1], which was carefully adiabatic. For a systematic study, we have performed 3D calculations to model new experiments that involve a nearly isotropic harmonic trap plus a rising 1D optical lattice. As seen in experiments with a 3D lattice [2], we find that the visibility of the interference pattern after atom release is close to unity immediately after ramping up the lattice, but then decreases after varying hold time. The decrease is most rapid when the lattice turnon is most rapid. Our calculations, using split operator methods applied to the timedependent GrossPitaevskii equation, qualitatively mimic the experimental results. The calculations show that quadrupole excitations associated with weak (50 Hz) transverse confinement can contribute to the reduction of the visibility of the interference pattern.\\[4pt] [1] Orzel et al., Science {\bf 291}, 2386 (2001). \\[0pt] [2] Gericke et al. J. Mod. Opt. {\bf 54}, 735 (2007). [Preview Abstract] 
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