Bulletin of the American Physical Society
47th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 61, Number 8
Monday–Friday, May 23–27, 2016; Providence, Rhode Island
Session M6: Excitations in Bose-Einstein Condensates |
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Chair: Stephen Eckel, Joint Quantum Institute (NIST/UMD) Room: 552AB |
Thursday, May 26, 2016 8:00AM - 8:12AM |
M6.00001: Classical and quantum reflection of bright matter-wave solitons Anna Marchant, Thomas Billam, Manfred Yu, Ana Rakonjac, John Helm, Christoph Weiss, Juan Polo, Simon Gardiner, Simon Cornish We report the controlled formation of a bright matter-wave soliton\footnote{A. L. Marchant et al., Nat. Commun. 4, 1865 (2013)} from a Bose--Einstein condensate of $^{85}$Rb\footnote{A. L. Marchant et al., Phys. Rev. A. 85, 053647 (2012)}. We demonstrate the reflection of the soliton from a broad repulsive Gaussian barrier and contrast this to the case of a repulsive condensate, in both cases finding excellent agreement with theoretical simulations using the 3D Gross-Pitaevskii equation. Using a tightly focussed red-detuned light sheet, we create a narrow attractive potential well, comparable in the narrow direction to the size of the soliton. Using a low incident velocity, we observe a splitting of the atomic wavepacket when it reaches the well, resulting in quantum reflection of $\sim$25\% of the atoms\footnote{A. L. Marchant et al., arXiv 1507.04639 (2015)}. In addition, a smaller fraction of atoms ($\sim$10\%) become trapped at the well. These results pave the way for new experimental studies of bright matter-wave soliton dynamics to elucidate the wealth of existing theoretical work and to explore an array of potential applications such as the study of short-range atom-surface potentials\footnote{S. L. Cornish et al., Physica D 238, 1299 (2009)}. [Preview Abstract] |
Thursday, May 26, 2016 8:12AM - 8:24AM |
M6.00002: The Formation of Phase Structure in the Creation of Soliton Trains Jason Nguyen, De Luo, Randall Hulet Matter-wave soliton trains were initially observed following an interaction quench in a condensate of ${^{7}\mathrm{Li}}$ atoms\footnote{K.E. Strecker, G.B. Partridge, A. G. Truscott, \& R. G. Hulet, Nature 417, 150 (2002).}. The relative phase between neighboring solitons was inferred to differ by $\pi$, giving the appearance of a repulsive interaction between them. The process by which this phase structure is formed is unknown. Starting with a condensate of ${^{7}\mathrm{Li}}$ atoms in the $|1,1\rangle$ state, we study the initial formation of soliton trains by quenching the magnetic field to rapidly vary the interaction from repulsive to attractive in a quasi-$1$-D system. We study the dynamics of the system shortly after the quench, using multiple in situ images. We previously used this technique to study soliton-soliton collisions\footnote{J. H. V. Nguyen, P. Dyke, D. Luo, B. A. Malomed, \& R. G. Hulet, Nature Physics 10, 918 (2014).}. [Preview Abstract] |
Thursday, May 26, 2016 8:24AM - 8:36AM |
M6.00003: Long-lived Dark Solitons in Ring-Trap Condensates Nick Proukakis, Donatello Gallucci We demonstrate the feasibility of generation of quasi-stable counter-propagating solitonic structures in an atomic Bose-Einstein condensate confined in a realistic toroidal geometry, and identify optimal parameter regimes for their experimental observation [1]. Using density engineering we numerically identify distinct regimes of motion of the emerging macroscopic excitations, including both solitonic motion along the azimuthal ring direction, such that structures remain visible after multiple collisions even in the presence of thermal fluctuations, and snaking instabilities leading to the decay of the excitations into vortical structures. Our analysis, which considers both mean field effects and fluctuations, is based on the JQC ring trap geometry [2]. References: Gallucci and Proukakis, New J. Phys. (Focus on Atomtronics-enabled Quantum Technologies) [to appear, 2016] (arXiv:1510.07078); [2] Murray et al. Phys. Rev. A 88 053615 (2013). [Preview Abstract] |
Thursday, May 26, 2016 8:36AM - 8:48AM |
M6.00004: A glimpse into the cosmic horizon problem: measuring topological defects in a supersonically expanding toroidal Bose-Einstein condensate Avinash Kumar, Stephen Eckel, Ian Spielman, Gretchen Campbell In standard (non-inflationary) cosmology, the expansion of the early universe occurs at a speed larger than the speed of light. This expansion produces a “horizon problem”: the expansion causes initially near-by points to separate at a velocity larger than that of light and become causally disconnected. We mimic this horizon problem in an ultracold atomic experiment by creating a sonic analog of the expansion of the early universe. Our experiment consists of neutral $^{23}$Na atoms trapped in an all optical ring that expands at supersonic speed. Because information can propagate only at the speed of sound, a supersonic expansion creates causally disconnected regions, whose phase evolve at different rates. After the expansion ends, these regions of different phase recombine, giving rise to spontaneous non-zero winding numbers when integrated around the whole ring in a manner similar to that envisioned by Kibble and Zurek. We measure the resulting winding number distribution as a function of initial radius, final radius, expansion time and sound speeds. We compare to a theory that connects the geometry and speed of expansion to the number of causally disconnected regions, finding good agreement with the winding number distribution predicted according to the geodesic rule. [Preview Abstract] |
Thursday, May 26, 2016 8:48AM - 9:00AM |
M6.00005: Minimally destructive Doppler measurement of a quantized, superfluid flow Neil Anderson, Avinash Kumar, Stephen Eckel, Sandro Stringari, Gretchen Campbell Ring shaped Bose-Einstein condensates are of interest because they support the existence of quantized, persistent currents. These currents arise because in a ring trap, the wavefunction of the condensate must be single valued, and thus the azimuthal velocity is quantized. Previously, these persistent current states have only been measured in a destructive fashion via either interference with a phase reference or using the size of a central vortex-like structure that appears in time of flight. Here, we demonstrate a minimally destructive, in-situ measurement of the winding number of a ring shaped BEC. We excite a standing wave of phonon modes in the ring BEC using a perturbation. If the condensate is in a nonzero circulation state, then the frequency of these phonon modes are Doppler shifted, causing the standing wave to precess about the ring. From the direction and velocity of this precession, we can infer the winding number of the flow. For certain parameters, this technique can detect individual winding numbers with approximately 90\% fidelity. [Preview Abstract] |
Thursday, May 26, 2016 9:00AM - 9:12AM |
M6.00006: The role of geometry in nonlocal superfluids. Kali Wilson, David Vocke, Ewan Wright, Francesco Marino, Iacopo Carusotto, Brian P. Anderson, Daniele Faccio In this work we perform numerical and experimental studies that demonstrate the key role of fluid geometry when the fluid is also nonlocal. We show that the Bogoliubov dispersion relation associated with elementary excitations in a nonlocal quantum fluid may be modified by the system geometry, such that the system can be pushed into a regime where superfluid behavior is observed despite a high degree of nonlocality. This interplay between geometry and nonlocality is a general feature of the nonlocal interaction, with applications to dipolar BECs and nonlocal photon fluids. Tailoring the system geometry thus provides external control of the effective nonlocal length characterizing the fluid, and sets a threshold wavevector below which a linear, sonic dispersion relation consistent with superfluidity may be observed. We discuss this interplay in the context of recent experimental observations of superfluid behavior in a room-temperature, nonlocal photon fluid in a propagating geometry. We have experimentally observed signatures of superfluid behavior in the dispersion relation, and in the nucleation of vortex cores as the photon fluid flows past an extended obstacle, despite working with a highly-nonlocal thermal nonlinearity expected to suppress such superfluid behavior. [Preview Abstract] |
Thursday, May 26, 2016 9:12AM - 9:24AM |
M6.00007: Collapse and revival of the monopole mode of a Bose-Einstein condensate in a spherical harmonic trap Victor Colussi, Cameron Straatsma, Matthew Davis, Dan Lobser, Murray Holland, Dana Anderson, Eric Cornell, Heather Lewandowski We observe the relaxation of the monopole (breathing) mode of a rubidium-87 Bose-Einstein condensate (BEC) in a highly spherical harmonic trap [1] at finite temperature. The experiments show a collapse and revival of the condensate oscillation, consistent with numerical simulations of the system using the Zaremba-Nikuni-Griffin methodology for the nonequilibrium dynamics of BECs [2]. The beating signal is shown to be due to the resonant excitation of the ``out-of-phase'' normal mode of the condensate and thermal cloud. [1] D. S. Lobser, A. E. S. Barentine, E. A. Cornell, and H. J. Lewandowski, Nat. Phys. 11, 1009 (2015). [2] E. Zaremba, T. Nikuni, and A. Griffin, J. Low Temp. Phys. 116, 277 (1999). [Preview Abstract] |
Thursday, May 26, 2016 9:24AM - 9:36AM |
M6.00008: Mechanisms of stimulated Hawking radiation in laboratory Bose-Einstein condensates Yi-Hsieh Wang, Ted Jacobson, Mark Edwards, Charles W. Clark We simulate and reproduce the results of a recent experiment \footnote{J. Steinhauer, {\em Nat. Phys.} {\bf 10}, 864 (2014)} that reported observations of a sonic analog black hole laser \footnote{S. Corley and T. Jacobson, {\em Phys. Rev. D} {\bf 59}, 124011 (1999)} in a Bose-Einstein condensate (BEC). In the experiment, a time-swept step potential was applied to a trapped cigar-shaped BEC of $^{87}$Rb, thereby creating white hole (WH) and black hole (BH) event horizons. Exponential growth of a density wave in the WH--BH cavity and the emission of Hawking radiation were observed. We show that the solution of the time-dependent Gross-Pitaevskii equation gives good agreement with the experiment with no adjustable parameters. The Hawking radiation in this experiment is not self-amplifying, but is stimulated by a growing Bogoliubov-\v{C}erenkov mode \footnote{I. Carusotto, S. X. Hu, L. A. Collins and A. Smerzi, {\em Phys. Rev. Lett.} {\bf 97}, 260403 (2006)} that is generated at the WH event horizon. We use scaling arguments to identify a class of feasible experiments that can provide more distinctive signatures of Hawking radiation and of the dominant Bogoliubov-\v{C}erenkov mode that stimulates it. [Preview Abstract] |
Thursday, May 26, 2016 9:36AM - 9:48AM |
M6.00009: Probing microscopic correlations from quantum depletion of a Bose-Einstein condensate Rockson Chang, Quentin Bouton, Hugo Cayla, Florence Nogrette, Christoph Westbrook, Alain Aspect, David Clement Interactions between particles can have a significant impact on the nature of the ground state of a quantum system. In the case of bosons at zero temperature, interactions lead to the population of higher energy states (momentum $|p|>0$) while depleting the condensate mode ($p=0$) [1]. The resulting many-body state exhibits strong correlations, such as pairing between particles of opposite momenta ($+p$ and $-p$), and characteristic $1/p$ tails in the momentum distribution [2]. Here I will present our recent progress towards observation of these signatures of quantum depletion in an ultracold lattice gas. Our experiments are performed with a gas of metastable Helium-4 atoms [3] for which three-dimensional electronic detection of individual particles is possible, providing direct access to the momentum-space correlations $g^{(2)}(p,p')$ [4]. Moreover, the high-resolution of our detection method allows for a careful investigation of the distribution $n(p)$ of the excited states, allowing us to distinguish between thermal and quantum contributions to the condensate depletion. [1] N. N. Bogoliubov, J. Phys. (Moscow) 11, 23 (1947) [2] L. Mathey et al, PRA 79, 013609 (2009) [3] Q. Bouton et al. PRA 91, 061402(R) (2015) [4] T. Jeltes et al., Nature 445, 402-405 (2007) [Preview Abstract] |
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