Bulletin of the American Physical Society
46th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 60, Number 7
Monday–Friday, June 8–12, 2015; Columbus, Ohio
Session G3: Quantum Dynamics in Bose-Einstein Condensates |
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Chair: Antoine Browaeyes, CNRS Institut d'Optique Room: Franklin AB |
Wednesday, June 10, 2015 8:00AM - 8:12AM |
G3.00001: Macroscopic quantum tunneling of a Bose-Einstein condensate through double Gaussian barriers Kenji Maeda, Gregor Urban, Matthias Weidem\"{u}ller, Lincoln D. Carr Macroscopic quantum tunneling is one of the great manifestations of quantum physics, not only showing passage through a potential barrier but also emerging in a many-body wave function. We study a quasi-1D Bose-Einstein condensate of Lithium, confined by two Gaussian barriers, and show that in an experimentally realistic potential tens of thousands of atoms tunnel on time scales of 10 to 100 ms. Using a combination of variational and WKB approximations based on the Gross-Pitaevskii or nonlinear Schr\"{o}dinger equation, we show that many unusual tunneling features appear due to the nonlinearity, including the number of trapped atoms exhibiting non-exponential decay, severe distortion of the barriers by the mean field, and even formation of a triple barrier in certain regimes. In the first 10ms, nonlinear many-body effects make the tunneling rates significantly larger than background loss rates, from 10 to 70Hz. Thus we conclude that macroscopic quantum tunneling can be observed on experimental time scales. [Preview Abstract] |
Wednesday, June 10, 2015 8:12AM - 8:24AM |
G3.00002: Birth of a quasi-stationary black hole in an outcoupled Bose-Einstein condensate Fernando Sols, Juan R. M. de Nova, David Guery-Odelin, Ivar Zapata We study the evolution of an initially confined atom condensate, which is progressively outcoupled by gradually lowering the confining barrier on one side. The goal is to identify protocols that best lead to a quasi-stationary sonic black hole separating regions of subsonic and supersonic flow. An optical lattice is found to be more efficient than a single barrier in yielding a long-time stationary flow. This is best achieved if the final conduction band is broad and its minimum is not much lower than the initial chemical potential. An optical lattice with a realistic Gaussian envelope yields similar results. We analytically prove and numerically check that, within a spatially coarse-grained description, the sonic horizon is bound to lie right at the envelope maximum. We derive an analytical formula for the Hawking temperature in that setup. Work appeared in New J. Phys. 16, 123033 (2014). [Preview Abstract] |
Wednesday, June 10, 2015 8:24AM - 8:36AM |
G3.00003: Universal dynamics in a Unitary Bose Gas Catherine Klauss, Xin Xie, Deborah Jin, Eric Cornell Starting with a $^{85}$Rb BEC, we investigate dynamics of a unitary Bose gas for timescales that are short compared to the three-body loss rates. We find that the momentum distribution of the unitary Bose gas evolves on timescales fast compared to losses, demonstrating that a unitary Bose gas can be created and probed dynamically, thus opening the door for further exploration of this novel strongly interacting quantum liquid. We further investigate whether the timescale for this evolution and the limiting shape of the momentum distribution are consistent with universal scaling with density. [Preview Abstract] |
Wednesday, June 10, 2015 8:36AM - 8:48AM |
G3.00004: Dynamics of impurities in ultracold Bose gas Yulia Shchadilova, Fabian Grusdt, Alexey Rubtsov, Eugene Demler A system of an impurity immersed in a Bose-Einstein condensate (BEC) exhibits the polaronic effect, which is known to be an ubiquitous phenomenon in a wide range of physical systems including semiconductors, doped Mott insulators, and high-Tc superconductors. Recent analysis of the BEC-polaron problem showed that existing analytical approaches do not provide reliable results in the experimentally relevant range of parameters when tested against Monte Carlo (MC) simulations [1]. In this contribution we demonstrate that the description of polarons at finite momentum can be done by employing an analytical class of wavefunctions based on the correlated Gaussian ansatz (CGWs) [2]. We show that CGWs show excellent agreement with known MC results for the polaron binding energy for a wide range of interactions. We discuss the properties of the polarons and atomic mixtures in systems of ultracold atoms in which polaronic effects can be observed with current experimental technology. Our CGWs predicts a specific pattern of correlations between host atoms that can be measured in time-of-flight experiments. [1] J. Vlietinck, et al arXiv:1406.6506; [2] Y. Shchadilova, et al arXiv:1410.5691; [3] F. Grusdt, et al arXiv:1410.2203 [Preview Abstract] |
Wednesday, June 10, 2015 8:48AM - 9:00AM |
G3.00005: Interaction assisted tunneling of a Bose-Einstein condensate out of a quasi bound state Shreyas Potnis, Ramon Ramos, Kenji Maeda, Lincoln D. Carr, Aephraim Steinberg We experimentally measure the tunneling rate of a $^{87}$Rb Bose-Einstein condensate prepared in a quasi-bound state. Using the combination of a magnetic quadrupole trap and a thin 1.1 $\mu$m barrier created using a blue-detuned sheet of light, we can create traps with controllable depth and lifetime. The thin tunnel barrier allows for a tunable tunneling rate from $30s{}^{-1}$ to $1s{}^{-1}$. The escape dynamics strongly depend on the mean-field energy, which gives rise to three distinct regimes--- classical over the barrier spilling, quantum tunneling, and decay dominated by background losses. We show that the tunneling rate goes down exponentially with decreasing chemical potential. Our results show good agreement with numerical solutions of the 3D Gross-Pitaevskii equation and WKB calculations. [Preview Abstract] |
Wednesday, June 10, 2015 9:00AM - 9:12AM |
G3.00006: Universal Loss Behavior of Trapped Finite-Temperature Unitary Bose Gases Ulrich Eismann, Lev Khaykovich, S{\'e}bastien Laurent, Igor Ferrier-Barbut, Benno S. Rem, Andrew T. Grier, Fr{\'e}d{\'e}ric Chevy, Christophe Salomon, Li-Chung Ha, Cheng Chin The low-temperature unitary Bose gas is a fundamental paradigm in few-body and many-body physics, attracting wide theoretical and experimental interest. We give an overview of a theory describing the dynamic interplay of two-body evaporation and three-body recombination in a trapped unitary atomic gas. We identify a magic trap depth where, within some parameter range, evaporative cooling is balanced by the recombination heating such that temperature stays constant. We perform independent experiments with $^7$Li and $^{133}$Cs atoms tuned to Feshbach resonances. These fully support the predictions of the model and enable quantitative measurements of both the trap depth, and the 3-body recombination rate in the low-temperature domain. We verify the validity of the universal dynamics for both species, for 2D and 3D evaporation, over two orders of magnitude in temperature and four orders of magnitude in three-body loss. [Preview Abstract] |
Wednesday, June 10, 2015 9:12AM - 9:24AM |
G3.00007: Macroscopic Quantum Tunneling of Bose-Einstein Condensates: Quantum Fluctuations, Entanglement, and Dynamics Diego Alcala, Joseph Glick, Lincoln D. Carr The quantum escape problem is famous in the context of quasi-bound states and chemical and nuclear reactions. We address three outstanding questions in this form of quantum tunneling. (1) How are tunneling rates modified by many-body effects, in particular beyond the mean field? (2) What is the role of higher order quantum effects like entanglement and correlations? (3) What is the dynamics of the escape process? To this end we study both repulsive and attractive Bose-Einstein condensates via matrix-product state methods for entangled dynamics. We find that entanglement is maximized when about half the particles have escaped. We find preliminary evidence that the time derivative of number fluctuations serves as an entanglement witness. [Preview Abstract] |
Wednesday, June 10, 2015 9:24AM - 9:36AM |
G3.00008: Response of a homogeneous Bose-Einstein condensate to an oscillating spatially-uniform force Nir Navon, Alexander Gaunt, Robert Smith, Zoran Hadzibabic The recent production of quasi-uniform Bose gases has offered new exciting possibilities to study out-of-equilibrium phenomena in nearly textbook systems. We explore the response of a homogeneous Bose-Einstein condensate to a time-oscillating constant-gradient potential. By tuning the amplitude and frequency of the modulation, as well as the atom number, we study the response of the BEC, from excitationless superflow to the turbulent regime. We probe the steady state of the driven system by measuring the momentum distribution using two-photon Bragg spectroscopy. [Preview Abstract] |
Wednesday, June 10, 2015 9:36AM - 9:48AM |
G3.00009: Superfluid internal convection in dilute Bose-Einstein condensates James Anglin, Lukas Gilz We apply quantum kinetic theory to heat transport in a Bose-condensed gas coupled collisionally to two spatially separated reservoir gases at different temperatures. We show that in the collisionless kinetic regime, where a Bogoliubov expansion is applicable, heat is transported by counter-propagating steady currents of condensate and non-condensate fractions , with the condensate flowing towards the source of greater heat. We derive explicit formulas for the steady state energy current and differential particle currents (with zero net particle flux). We estimate that the effect should be cleanly observable in currently feasible experiments: the condensate and thermal fraction should separate in ballistic expansion. [Preview Abstract] |
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