Bulletin of the American Physical Society
49th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics APS Meeting
Volume 63, Number 5
Monday–Friday, May 28–June 1 2018; Ft. Lauderdale, Florida
Session J04: Nonequilibrium Dynamics |
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Chair: Logan W. Clark, University of Chicago Room: Grand C |
Wednesday, May 30, 2018 10:30AM - 10:42AM |
J04.00001: On-demand Smooth Flow by Stirring a Racetrack Atom Circuit Mark Edwards, Olatunde Oladehin, Benjamin Eller, Charles Clark We studied how smooth flow can be produced by stirring an ultracold atom circuit consisting of a gaseous Bose--Einstein condensate (BEC) confined in a ``racetrack'' potential. We assume that the BEC is strongly confined in a horizontal plane by a vertical harmonic trap and, within this plane, subjected to an arbitrary two--dimensional potential using laser light. The racetrack potential is made up of two straight parallel channels of length L connected on both ends by semicircular channels of the same width and (energy) depth as the straightaways. We used the Gross--Pitaevskii equation (GPE) to simulate the behavior of the BEC in this potential when stirred by a rectangular paddle at various speeds and barrier heights. For fixed L we stirred the BEC at four different speeds and with barrier heights that varied from 0.5$\mu$ to 2.0$\mu$. This series of conditions was performed for seven different values of L. We also devised a simple 1D model of the stirring of the BEC based on the GPE in order to understand how smooth flow is produced by stirring. This understanding should enable the design of a stirring sequence that would produce a given flow on demand. [Preview Abstract] |
Wednesday, May 30, 2018 10:42AM - 10:54AM |
J04.00002: Finite-temperature Effects on Producing Smooth Flow in a Racetrack Atom Circuit Benjamin Eller, Olatunde Oladehin, Charles Clark, Mark Edwards We studied smooth flow produced by stirring an ultracold atom circuit consisting of a gaseous Bose--Einstein condensate (BEC) confined in a ``racetrack'' potential at finite temperature. The BEC is assumed to be strongly confined in a horizontal plane by a vertical harmonic trap and, within this plane, subjected to an arbitrary two--dimensional potential. The racetrack potential is made up of two straight parallel channels connected on both ends by semicircular channels of the same width and (energy) depth as the straightaways. We used the Zaremba--Nikuni--Griffin model to simulate the behavior of the BEC and noncondensate in this potential when stirred by a rectangular paddle at various speeds and barrier heights. We compare the amount of flow produced by stirring under these conditions with the flow produced under the same conditions but at zero temperature. We discuss how a simple model which predicts the flow produced by stirring at zero temperature could be modified for finite temperature. [Preview Abstract] |
Wednesday, May 30, 2018 10:54AM - 11:06AM |
J04.00003: Self-trapping bifurcation drives macroscopic-superposition in double well Josephson oscillations. Shane Kelly, Eddy Timmermans, Shan-Wen Tsai Double well BEC-tunneling exhibits two distinct oscillatory modes: free oscillations around a zero population imbalance and self-trapping oscillations around a nonzero population imbalance. Distinct eigen-state sectors are associated with each of the oscillation behaviors and the sectors are separated by a bifurcation point. We predict (and have numerically observed) that an initial semi-classical state which overlaps with both sectors displays interference between the two oscillatory modes and evolves a macroscopic supper-position state. The interference between the two oscillations is most clearly observed by an asymmetry biased toward free oscillations. By quantifying the divergence from the classical mean-field state, we found the state with maximum non-classical structure produced during its time-evolution. Initial states which have asymmetric evolution also evolve into maximally non-classical states with macroscopic superposition. For the most asymmetric oscillations, the macroscopic superposition is significant for over a quarter of a period and observable by an experiment that, after a given time, interval counts the number of atoms in one of the wells. [Preview Abstract] |
Wednesday, May 30, 2018 11:06AM - 11:18AM |
J04.00004: Nonequilibrium properties of the driven-dissipative Ising model Andrew Koller, Anzi Hu, James Clark, Daniel Paz, Mohammad Maghrebi We study numerically the dynamics and steady state properties of a transverse-field Ising model coupled to a dissipative bath. In certain parameter regimes the non-equilibrium quantum system can be mapped to a classical Ising model at an effective temperature determined by the transverse field and the dissipation. We also discuss if, and how, the dynamics can be effectively described by a stochastic spin model. [Preview Abstract] |
Wednesday, May 30, 2018 11:18AM - 11:30AM |
J04.00005: Correlations of Bose fireworks emission from strongly driven Bose-Einstein condensates. Lei Feng, Jiazhong Hu, Logan W. Clark, Cheng Chin Bose-Einstein condensates with oscillating interactions enables exciting opportunities to study~far from equilibrium~dynamics in quantum many-body~physics. Based on a fast modulation of magnetic field near a Feshbach resonance, we observe high harmonic generation~of matter-wave jets~from cesium~condensates.~The quantization of energy and momentum of atoms in the jets results from the Bose stimulation.~With the assistance of pattern recognition, we are able to identify~various scattering processes that leads to the pattern,~further confirmed by~correlation analysis. We also observe intricate high-order correlations~which can not be fully decomposed to lower order correlations.~Our observation can be modeled based on the hierarchy of inelastic collisions between atoms in the driven condensate. [Preview Abstract] |
Wednesday, May 30, 2018 11:30AM - 11:42AM |
J04.00006: Numerical Simulation of Matter-wave Jets in Driven Bose-Einstein Condensates. Han Fu, Lei Feng, Brandon Anderson, Logan Clark, Jiazhong Hu, Jeffery Andrade, Cheng Chin, Kathryn Levin Recent experimental work by Clark et al. in Nature 551, 356 (2017) reported a collective emission of matter-wave jets in a modulated bosonic condensate. Here the inter-atomic interactions are time-dependent because of the oscillating magnetic field. We use time dependent Gross-Pitaevskii theory to simulate these experiments and demonstrate good agreement with the data under experimental conditions. Despite the rather violent emission of matter-wave jets, there is considerable systematics in the underlying behavior. Of interest is the observation of a sequence of rings in momentum space with radii following the power law as N$^{\mathrm{1/2}}$, where N $=$ 1, 2, 3\textellipsis is the order of the ring. We characterize the angular correlation functions g$^{\mathrm{2}}$ and g$^{\mathrm{3}}$ of the emitted atoms and show that both compare favorably with experiment. We extract phase information from our simulations to provide further insights into the quantum coherence of the stimulated processes. We end by addressing how this simple dynamical condensate theory can capture the essential features of matter-wave jets. [Preview Abstract] |
Wednesday, May 30, 2018 11:42AM - 11:54AM |
J04.00007: Domain-wall dynamics in stable spin domains in a non-degenerate gas J.M. McGuirk, S.D. Graham, D. Niroomand, R.J. Ragan We demonstrate the existence of stable spin domains in a weakly interacting gas of $^{87}$Rb atoms above quantum degeneracy. Coherent exchange interactions, when combined with optically-generated inhomogeneous effective magnetic fields, produce long-lived steady-state domains. By studying the relaxation of the domain wall, we identify the external field gradients that stabilize the initial spin domain structures. We compare our results with hydrodynamic and collisionless solutions to a kinetic equation and show good quantitative agreement across a wide range of densities and temperatures. [Preview Abstract] |
Wednesday, May 30, 2018 11:54AM - 12:06PM |
J04.00008: Domain wall dynamics of a non-degenerate gas Robert Ragan, SD Graham, D Niroomand, JM McGuirk In recent experiments, we have observed the dynamics of spin domains in a trapped gas of weakly interacting Rb-87 atoms above quantum degeneracy over a wide range of densities and effective magnetic field gradients. We have analyzed the long-lived domain wall structures as well as the transient dynamics using a kinetic equation in which quantum exchange is described in terms of identical spin rotation. For high densities, a stable hydrodynamic domain wall solution is in good quantitative agreement with experiment and computer simulations. For low densities, where the mean-free path is comparable to the length of the cloud, a moments approach gives results that agree with the lifetime and size of the observed transients. [Preview Abstract] |
Wednesday, May 30, 2018 12:06PM - 12:18PM |
J04.00009: Non-Perturbative Dynamical Effects in Nearly Scale Invariant Systems: The Action of Breaking Scale Invariance Jeff Maki, Li-Ming Zhao, Fei Zhou In this talk we put forward a general formalism that categorizes the action of breaking scale invariance in the non-equilibrium dynamics of non-relativistic quantum systems. This approach can be applied to a wide range of systems, regardless of the number of particles or their statistics. We show that in three dimensions, any small deviation from the strongly interacting fixed point leads to non-perturbative effects in the long-time limit. The scale invariant dynamics are altered by a non-pertubative log-periodic beat, the presence of which is universal and depends only on the deviation from the resonant fixed point. [Preview Abstract] |
Wednesday, May 30, 2018 12:18PM - 12:30PM |
J04.00010: The relations between quantum Zeno/anti-Zeno effect and parity-time symmetric Hamiltonian Jiaming Li, Zhao Wang, Le Luo, Yogesh Narayan Joglekar Recently dissipative trapped atoms have been used to realize parity-time (PT) symmetric non-Hermitian Hamiltonians $^{\mathrm{[1]}}$. Such systems not only exhibit novel symmetry breaking properties, but also indicate its subtle relation with the measurement effects in quantum decay processes, known as quantum Zeno or anti-Zeno effect (QZE/AZE). In this talk, we will present the experimental results of simulating PT-symmetric Hamiltonians with dissipative ultracold $^{\mathrm{6}}$Li atoms in various cases, including static dissipation, Floquet dissipation, and Floquet coupling. Our observation shows that static and Floquet dissipation relate to the continuous QZE and the pulsed QZE, respectively. We then compare the similarity between the Floquet dissipation case and the previous QZE/AZE observed in the lattice tunneling experiments$^{\mathrm{\thinspace [2]}}$. Our findings enable PT-symmetric Hamiltonian to be a useful tool for analyzing QZE/AZE, particularly for their counterparts in the weak dissipation or measurement regimes. [1] J. Li et al. arXiv:1608.05061 [2]M.C. Fischer et al. Phys. Rev. Lett. 87, 040402, 2001 [Preview Abstract] |
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