Bulletin of the American Physical Society
48th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 62, Number 8
Monday–Friday, June 5–9, 2017; Sacramento, California
Session J3: Nonlinear Dynamics and Outofequilibrium Trapped Gases 
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Chair: Michael Kohl, University of Bonn Room: 308 
Wednesday, June 7, 2017 2:00PM  2:12PM 
J3.00001: Merging of independent condensates: disentangling the KibbleZurek mechanism JeanLoup Ville, Monika Aidelsburger, Raphael SaintJalm, Sylvain Nascimbene, Jerome Beugnon, Jean Dalibard An important step in the study of outofequilibrium physics is the KibbleZurek theory which describes a system after a quench through a secondorder phase transition. This was studied in our group with a temperature quench across the normaltosuperfluid phase transition in an annular trap geometry, inducing the formation of supercurrents. Their magnitude and direction were detected by measuring spiral patterns resulting from the interference of the ringshaped condensate with a central reference disk. According to the KZ mechanism domains of phase are created during the quench, with a characteristic size depending of its duration. In our case this results in a stochastic formation of supercurrents depending on the relative phases of the domains. As a next step of this study, we now design ourselves the patches thanks to our tunable trapping potential. We control both the number of condensates to be merged (from one to twelve) and their merging time. We report an increase of the vorticity in the ring for an increased number of patches compatible with a random phase model. We further investigate the time required by the phase to homogenize between two condensates. [Preview Abstract] 
Wednesday, June 7, 2017 2:12PM  2:24PM 
J3.00002: Spontaneous Generation and Evolution of Defects in a Quenched Bose Gas Nick Proukakis, IKang Liu, ShihChuan Gou, Simone Donadello, Simone Serafini, Tom Bienaime, Giacomo Lamporesi, Gabriele Ferrari, Franco Dalfovo We provide a detailed numerical analysis of the Trento experiments with quenched BoseEinstein condensates in an elongated harmonic trap (Donadello et al., PRA 94, 023628 (2016)) where defects in the order parameter are spontaneously generated by the KibbleZurek mechanism. Using the stochastic projected GrossPitaevskii equation, and by quenching both temperature and chemical potential, we are able to capture both the earlytime phase transition dynamics and the observed longterm coarsegraining evolution, reproducing the experimentallyobserved condensate growth dynamics, and longterm defect evolution. The emerging picture sheds light into how the initial thermal state passes through a transient “turbulent” state of many highlyexcited vortical structures, before settling into a few interacting longlived solitonic vortices. By numerically tracking the number of spontaneouslyformed defects during and after the quench, we quantify the dependence of vortex number, vortex linelength and coherence length on quench rate, also demonstrating the observed breakdown of KibbleZurek scaling for fast quenches, arising as a result of coarsegraining dynamics prior to experimental measurements. [Preview Abstract] 
Wednesday, June 7, 2017 2:24PM  2:36PM 
J3.00003: Quenches from finitetemperature ultracold matter Ian G. White, Kaden R. A. Hazzard Although interaction quenches are known to drive interesting dynamics, much prior work has focused on quenches initiated from states that are near the ground state. In contrast, experiments in ultracold matter  from fermionic atoms in optical lattices to dipolar molecules  are often outside this regime, necessitating the study of quenches from higher temperature states. Although in equilibrium, high temperatures are usually associated with trivial, structureless states, driving such states out of equilibrium can lead to rich behavior. For example, we have recently shown that starting from a hot, uncorrelated state of fermions in an optical lattice and evolving it in time leads to substantial intricatelystructured correlations between sites  even without interactions during the dynamics. Because including interactions challenges existing theoretical methods (both numerical and analytic) we are developing tools that exploit the nature of the hightemperature initial conditions to calculate these dynamics. We will describe and analyze the accuracy of one such method, a dynamic numerical linked cluster expansion, and its applications to spin systems relevant to cold atoms. [Preview Abstract] 

J3.00004: ABSTRACT WITHDRAWN 
Wednesday, June 7, 2017 2:48PM  3:00PM 
J3.00005: Nonequilibrium phase transitions in a drivendissipative system of interacting bosons Jeremy T. Young, Michael FossFeig, Alexey V. Gorshkov, Mohammad F. Maghrebi Atomic, molecular, and optical systems provide unique opportunities to study simple models of drivendissipative manybody quantum systems. Typically, one is interested in the resultant steady state, but the nonequilibrium nature of the physics involved presents several problems in understanding its behavior theoretically. Recently, it has been shown that in many of these models, it is possible to map the steadystate phase transitions onto classical equilibrium phase transitions. In the language of Keldysh field theory, this relation typically only becomes apparent after integrating out massive fields near the critical point, leaving behind a single massless field undergoing nearequilibrium dynamics. In this talk, we study a drivendissipative XXZ bosonic model and discover critical points at which two fields become gapless. Each critical point separates three different possible phases: a uniform phase, an antiferromagnetic phase, and a limit cycle phase. Furthermore, a description in terms of an equilibrium phase transition does not seem possible, so the associated phase transitions appear to be inherently nonequilibrium. [Preview Abstract] 
Wednesday, June 7, 2017 3:00PM  3:12PM 
J3.00006: Collective manybody bounce in the breathingmode oscillations of a finitetemperature TonksGirardeau gas. Karen Kheruntsyan, Yasar Atas, Isabelle Bouchoule, Dimitri Gangardt We analyse the breathingmode oscillations of a harmonically quenched TonksGiradeau (TG) gas using an exact finitetemperature dynamical theory. We predict a striking collective manifestation of impenetrabilitya collective manybody bounce effect. The effect, while being invisible in the evolution of the \emph{in situ} density profile of the gas, can be revealed through a nontrivial periodic narrowing of its momentum distribution, taking place at twice the rate of the fundamental breathingmode frequency of oscillations of the density profile. We identify physical regimes for observing the manybody bounce and construct the respective nonequilibrium phase diagram as a function of the quench strength and the initial equilibrium temperature of the gas. We also develop a finitetemperature hydrodynamic theory of the TG gas, wherein the manybody bounce is explained by an increased thermodynamic pressure during the isentropic compression cycle, which acts as a potential barrier for the particles to bounce off. [Preview Abstract] 
Wednesday, June 7, 2017 3:12PM  3:24PM 
J3.00007: Exploring collective spin dynamics in a weakly interacting gas of fermions Scott Smale, Andrew Koller, Ben A. Olsen, Haille Sharum, Chris Luciuk, Stefan Trotzky, Ana Maria Rey, Joseph H. Thywissen Strongly correlated states are often associated with strongly interacting regimes. However, weak interactions can also lead to strong correlations, given sufficiently long coherent interaction times. Ultracold atomic Fermi gases, with precisely controllable parameters, offer a versatile platform to investigate the emergence of collective behavior in outofequilibrium settings. Here we present observations of nontrivial collective behavior that emerges in the spin dynamics of a gas of $^{40}$K atoms in the weakly interacting regime. Starting with a spinpolarized gas, we study collective spin dynamics in a Ramsey sequence, both with and without a spinreversal pulse. We observe large oscillations with life times up to 100 milliseconds. In contrast to demagnetization in the strongly interacting regime, there are multiple revivals. Experimental results are compared to a fully quantum model that maps motional trap states with swave scattering onto a spin chain with longrange interactions. The broader impact of this study is an improved understanding of magnetic correlations driven by the exchange interactions between itinerant spins. [Preview Abstract] 
Wednesday, June 7, 2017 3:24PM  3:36PM 
J3.00008: Spin diffusion of ultracold 87Rb in inhomogeneous spindependent potentials Jeffrey McGuirk, Dorna Niroomand, Sean Graham We study the effect of an inhomogeneous differential potential on the relaxation dynamics of spin structures in ultracold $^{87}$Rb near degeneracy. In a homogeneous differential potential, the diffusion of spin inhomogeneities has been shown to exhibit instabilities that interconvert longitudinal and transverse spin. These instabilities couple transverse and longitudinal spin dynamics and lead to largescale coherent spin fluctuations. However, the addition of a spatially inhomogeneous spindependent potential is predicted to suppress this instability and decouple the spin dynamics. We present progress towards observing this phenomenon by measuring the diffusion of a longitudinal domain wall in the presence of an opticallycreated inhomogeneous differential potential. We observe trapping of a transverse spin wave within the domain wall and a separation of timescales for transverse and longitudinal spin relaxation, indicative of anisotropic spin diffusion. We also study the role of coherence in these dynamics. [Preview Abstract] 
Wednesday, June 7, 2017 3:36PM  3:48PM 
J3.00009: Faster than Exponential Decay of OutofTimeOrdered Correlators Lea Santos, E. Jonathan TorresHerrera In studies of nonequilibrium quantum dynamics, several attempts have been made to connect the exponential decay rate of the Loschmidt echo and the survival probability with the classical Lyapunov exponent. The same idea has been recently extended to the outoftimeordered fourpoint correlator (OTOC). We show that the OTOC, just like the survival probability, may in fact show faster than exponential decays. This occurs not only for chaotic manybody quantum systems with level repulsion, but also for integrable models. [Preview Abstract] 
Wednesday, June 7, 2017 3:48PM  4:00PM 
J3.00010: Parametric Cooling of Ultracold Atoms Matthew Boguslawski, Bharath H. M., Maryrose Barrios, Michael Chapman An oscillator is characterized by a restoring force which determines the natural frequency at which oscillations occur. The amplitude and phasenoise of these oscillations can be amplified or squeezed by modulating the magnitude of this force (e.g. the stiffness of the spring) at twice the natural frequency. This is parametric excitation; a longstudied phenomena in both the classical and quantum regimes. Parametric cooling, or the parametric squeezing of thermomechanical noise in oscillators has been studied in micromechanical oscillators [1] and trapped ions [2]. We study parametric cooling in ultracold atoms. This method shows a modest reduction of the variance of atomic momenta, and can be easily employed with preexisting controls in many experiments. Parametric cooling is comparable to deltakicked cooling [3], sharing similar limitations. We expect this cooling to find utility in microgravity experiments where the experiment duration is limited by atomic free expansion. [1] D. Rugar and P. Gr\"{u}tter, Phys. Rev. Lett., 67:699 (1991) [2] V. Natarajan, et al., Phys. Rev. Lett., 74:2855(1995) [3] H. Ammann, N. Christensen, Phys. Rev. Lett., 78:2088 (1997) T. Kovachy, et al., Phys. Rev. Lett., 114:143004 (2015) [Preview Abstract] 
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