Bulletin of the American Physical Society
2013 Joint Meeting of the APS Division of Atomic, Molecular & Optical Physics and the CAP Division of Atomic, Molecular & Optical Physics, Canada
Volume 58, Number 6
Monday–Friday, June 3–7, 2013; Quebec City, Canada
Session M1: Non-equilibrium Dynamics II |
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Chair: Andrew Daley, University of Pittsburgh Room: 200A |
Thursday, June 6, 2013 8:00AM - 8:12AM |
M1.00001: Bath-induced band-decay in a spin-dependent optical lattice Brian DeMarco, David Chen, Carolyn Meldgin We have measured the bath-induced band-decay rate for a thermal gas of $^{87}$Rb atoms trapped in a cubic, fully spin-dependent optical lattice. Atoms in the $\left|F=1,m_F=-1\right\rangle$ state are confined in the lattice and driven to the first-excited band via stimulated Raman transitions. We compare rates for decay to the ground band in the presence and absence of a bath consisting of a $\left|F=1,m_F=0\right\rangle$ BEC that does not experience the lattice potential. For lattice depths in the Mott-insulator regime, we measure increased decay rates induced by the bath atoms. This talk will include a discussion of decay mechanisms, and the importance of bath-induced decay to proposed methods for cooling quasimomentum distributions in a lattice. [Preview Abstract] |
Thursday, June 6, 2013 8:12AM - 8:24AM |
M1.00002: Far-from-equilibrium dynamics of spin models describing ultracold molecules and ions Kaden Hazzard, Salvatore Manmana, Michael Foss-Feig, John Bollinger, Ana Maria Rey Motivated by ongoing ultracold molecule and trapped ion experiments, we show that quenches of internal degrees of freedom lead to rich, informative dynamics already under \textit{present} experimental conditions. Molecules frozen in an optical lattice and trapped ions each implement quantum spin models of great interest in condensed matter physics. Molecules' rotational and ions' nuclear/electronic states serve as effective spins. We show that one can implement quenches via standard microwave Ramsey spectroscopy, and that the resulting dynamics can be used to (i) benchmark how accurately spin models describe the systems, (ii) create entangled, metrologically useful squeezed states, and (iii) explore qualitatively novel regimes of dynamic behavior that display nonanalytic time dependence and universality. For molecules, this is possible even with current ultracold but nondegenerate temperatures and densities [1]. For ions, the temperature and density are better controlled, but decoherence is relevant. Nevertheless, the features described above survive experimentally relevant decoherence [2]. \\[4pt] [1] K.~R.~A. Hazzard, S.~R. Manmana, M. Foss-Feig, and A.~M. Rey, PRL (to appear), arxiv:1209.4076 \\[0pt] [2] M. Foss-Feig, K.~R.~A. Hazzard, J.~J. Bollinger, and A.~M. Rey, arxiv:1209.5795 [Preview Abstract] |
Thursday, June 6, 2013 8:24AM - 8:36AM |
M1.00003: Conduction properties of strongly interacting Fermions Jean-Philippe Brantut, David Stadler, Sebastian Krinner, Jakob Meineke, Tilman Esslinger We experimentally study the transport process of ultracold fermionic atoms through a mesoscopic, quasi two-dimensional channel connecting macroscopic reservoirs. By observing the current response to a bias applied between the reservoirs, we directly access the resistance of the channel in a manner analogous to a solid state conduction measurement. The resistance is further controlled by a gate potential reducing the atomic density in the channel, like in a field effect transistor. In this setup, we study the flow of a strongly interacting Fermi gas, and observe a striking drop of resistance with increasing density in the channel, as expected at the onset of superfluidity. We relate the transport properties to the in-situ evolution of the thermodynamic potential, providing a model independant thermodynamic scale. The resistance is compared to that of an ideal Fermi gas in the same geometry, which shows an order of magnitude larger resistance, originating from the contact resistance between the channel and the reservoirs. The extension of this study to a channel containing a tunable disorder is briefly outlined. [Preview Abstract] |
Thursday, June 6, 2013 8:36AM - 8:48AM |
M1.00004: Non-destructive Faraday imaging of dynamically controlled ultracold atoms Miroslav Gajdacz, Poul L. Pedersen, Troels M{\o}rch, Andrew J. Hilliard, Jan Arlt, Jacob F. Sherson We investigate non-destructive measurements of ultra-cold atomic clouds based on dark field imaging of spatially resolved Faraday rotation [1]. In particular, we pursue applications to dynamically controlled ultracold atoms. The dependence of the Faraday signal on laser detuning, atomic density and temperature is characterized in a detailed comparison with theory. In particular the destructivity per measurement is extremely low and we illustrate this by imaging the same cloud up to 2000 times. The technique is applied to avoid the effect of shot-to-shot fluctuations in atom number calibration. Adding dynamic changes to system parameters, we demonstrate single-run vector magnetic field imaging and single-run spatial imaging of the system's dynamic behavior. The method can be implemented particularly easily in standard imaging systems by the insertion of an extra polarizing beam splitter. These results are steps towards quantum state engineering using feedback control of ultracold atoms. M. Gajdacz et al, arXiv:1301.3018 [Preview Abstract] |
Thursday, June 6, 2013 8:48AM - 9:00AM |
M1.00005: A Superheated Bose-Condensed Gas Richard Fletcher, Alexander Gaunt, Robert Smith, Zoran Hadzibabic Our understanding of various states of matter usually relies on the assumption of thermodynamic equilibrium. However, the transitions between different phases of matter can be strongly affected by non-equilibrium phenomena. Here we demonstrate and explain an example of non-equilibrium stalling of a continuous, second-order phase transition. We create a superheated atomic Bose gas, in which a Bose-Einstein condensate (BEC) persists above the equilibrium critical temperature, Tc, if its coupling to the surrounding thermal bath is reduced by tuning interatomic interactions. For vanishing interactions the BEC persists in the superheated regime for a minute. However, if strong interactions are suddenly turned on, it rapidly ``boils'' away. Our observations can be understood within a two-fluid picture, treating the condensed and thermal components of the gas as separate equilibrium systems with a tuneable inter-component coupling. We experimentally reconstruct a non-equilibrium phase diagram of our gas, and theoretically reproduce its main features. [Preview Abstract] |
Thursday, June 6, 2013 9:00AM - 9:12AM |
M1.00006: Evolution of a Driven Quantum System Toward a Quasi-Thermal State Herbert F. Fotso, Karlis Mikelsons, James K. Freericks We study the relaxation of an interacting system driven out of equilibrium by a constant electric field using Non-Equilibrium Dynamical Mean Field Theory. We use on the one hand a DMFT method which solves the steady state problem directly in frequency space, and on the other hand, a DMFT method that follows the transient time evolution of the system on the Keldysh contour. The system is described by the Falicov Kimball model which we follow across the metal - insulator transition. We find that the retarded Green's function quickly approaches that of the steady state while the lesser Green's function and, as a result the distribution function, slowly approach that of a steady state with an increased temperature due to the additional energy transferred to the system by the electric field. Analyses of this type can help understand the results of some experiments involving ultracold atomic gases. [Preview Abstract] |
Thursday, June 6, 2013 9:12AM - 9:24AM |
M1.00007: Instabilities dynamics in an ultra-cold Bose gas Dorna Niroomand, Lydia Zajiczek, Jeffrey McGuirk The presence of a spin discontinuity in an ultra-cold gas has a dramatic effect on the dynamics of the system. In particular, the sudden reversal of spin across a domain wall can cause even the smallest spin perturbations to grow into macroscopic coherent oscillations. We report progress towards realizing such an instability in a magnetically trapped gas of $^{87}$Rb atoms. Using optical patterning techniques, we create a sharp spin gradient in a gas just above quantum degeneracy. We observe instability-induced rapid and sudden spin inversions and characterize their time scales. [Preview Abstract] |
Thursday, June 6, 2013 9:24AM - 9:36AM |
M1.00008: Matter-field quadrature interferometry for nonequilibrium ultracold atoms in optical lattices Philip Johnson, Eite Tiesinga We propose an interferometric technique for making time-resolved measurements of matter-field quadrature operators for nonequilibrium ultracold atoms in optical lattices. The technique creates two subsystems of atoms---the arms of the interferometer---in different spin states and lattice sites. A Feshbach resonance turns off atom-atom interactions in one spin subsystem, making it a well-characterized reference state, while atoms in the other subsystem undergo nonequilibrium dynamics for a variable hold time. The dynamics can involve a variety of Hamiltonians and lattice geometries (e.g., cubic, honeycomb, superlattices), including systems with tunneling, spin orbit couplings using artificial gauge fields, and perturbations from external fields. Interfering the subsystems via a second beam-splitting operation, quadrature observables are mapped directly onto the relative spin populations. In this talk, I describe the general technique and then present analytic results for the special case a deep lattice with negligible tunneling. I also describe how the interferometer can be used to determine atom-atom interaction strengths and test the physics of so-called super-Heisenberg scaling. [Preview Abstract] |
Thursday, June 6, 2013 9:36AM - 9:48AM |
M1.00009: Quantum catastrophes and ergodicity in the dynamics of bosonic Josephson junctions Duncan O'Dell We study rainbow (fold) and cusp catastrophes that form in Fock space following a quench in a Bose Josephson junction [1]. In the Gross-Pitaevskii mean-field theory the rainbows are singular caustics, but in the second-quantized theory a Poisson resummation of the wave function shows that they are described by well behaved Airy functions. The structural stability of these Fock space caustics against variations in the initial conditions and Hamiltonian evolution is guaranteed by catastrophe theory. We also show that the long-time dynamics are ergodic. Our results are relevant to the question posed by Berry [2]: are there circumstances when it is necessary to second-quantize wave theory in order to avoid singularities?\\[4pt] [1] D.H.J. O'Dell, Phys. Rev. Lett. \textbf{109}, 150406 (2012)\\[0pt] [2] M.V. Berry, Nonlinearity \textbf{21}, T19 (2008) [Preview Abstract] |
Thursday, June 6, 2013 9:48AM - 10:00AM |
M1.00010: Generalized Gibbs Ensemble vis a vis Standard Thermodynamics: A Rigorous Lower Bound on Accuracy Gain Maxim Olshanii Consider a situation where one additional integral of motion is incorporated into an existing microcanonical description of a quantum system. For these two ensembles, we compare their abilities to predict the value of a particular observable after a relaxation from an initial non-equilibrium state. We derive a rigorous lower bound on the accuracy gain resulting from an additional conserved quantity. For a sufficiently fine microcanonical partitioning of the axis of the additional integral, the bound does not depend on the details of this partitioning. Instead, there, a recently introduced Frobenius-Hilbert-Schmidt inner product between the integral of motion and the observable of interest naturally emerges [M.\ Olshanii, arXiv:1208.0582]. The bound can be used to optimise the choice of integrals of motion for Generalized Gibbs Ensembles. We illustrate our findings on a numerical example of momentum distributions of lattice hard-core bosons with soft-core repulsion after a quench of the soft-core strength. [Preview Abstract] |
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