Bulletin of the American Physical Society
38th Annual Meeting of the Division of Atomic, Molecular, and Optical Physics
Volume 52, Number 7
Tuesday–Saturday, June 5–9, 2007; Calgary, Alberta, Canada
Session B4: Vortices and Solitons in Bose-Einstein Condensates |
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Chair: M. Kraemer, University of Colorado Room: TELUS Convention Centre Glen 206 |
Wednesday, June 6, 2007 10:30AM - 10:42AM |
B4.00001: Exchange of Spin and Orbital Angular Momentum Between an Ultracold Bose Gas and Optical Angular Momentum Beams Kevin C. Wright, Andrew B. Kowalik, L. Suzanne Leslie, Michael V. Pack, Nicholas P. Bigelow Atoms and photons possess both spin and orbital angular momentum degrees of freedom, which can be coupled under appropriate experimental conditions. Using Laguerre Gaussian laser beams of differing intrinsic angular momentum and polarization, we have investigated various aspects of how the spin and orbital angular momentum of the photons couple to either a nondegenerate or degenerate (BEC) bose gas. In particular, we have focused on exploring the conditions under which it is possible to coherently transfer orbital angular momentum to an ultracold cloud of $^{87}$Rb via a two-photon stimulated Raman transition between magnetic sublevels. [Preview Abstract] |
Wednesday, June 6, 2007 10:42AM - 10:54AM |
B4.00002: Persistent flow in a Bose-Einstein condensate Pierre Clade, Changhyun Ryu, Mikkel Andersen, Vasant Natarajan, Anand Ramanathan, Kristian Helmerson, William Phillips We will describe experiments on the study of quantized flow of Bose-condensed atoms in a multiply-connected trap. This torus-shaped trap is formed by the combination of an elliptically shaped, magnetic trap with a blue detuned laser beam in the middle to exclude atoms from the center of the magnetic trap. The rotation was initiated by transferring the orbital angular momentum from Laguerre-Gaussian photons to the atoms. We have observed that the rotational flow of atoms persists for several seconds, even when the condensate fraction is less than 10\%. We have also observed flow with high angular momentum and its splitting into singly charged vortices when the trap in no longer multiply-connected. [Preview Abstract] |
Wednesday, June 6, 2007 10:54AM - 11:06AM |
B4.00003: Quantum dynamics of Raman-coupled Bose-Einstein condensates with Laguerre-Gaussian beams Rina Kanamoto, Ewan Wright, Pierre Meystre We study the quantum dynamics of Bose-Einstein condensates driven by Laguerre-Gaussian light beams. Due to the helical structure of the laser field, the orbital angular momentum of the photon is transferred to the atoms, resulting in a condensate in a coherent superposition of two components with distinct center-of-mass angular momenta. The quantization of the matter-wave field is found to exhibit the collapse and revivals in the resulting interference pattern between two components. The period of the collapse and revivals depends on the U(1) symmetry of the matter wave and is directly observable as the off-axis motion of quantized vortices in the condensate density. We further analyze the steady-state population transfer that can be achieved when applying a time-dependent two-photon detuning. [Preview Abstract] |
Wednesday, June 6, 2007 11:06AM - 11:18AM |
B4.00004: Vortex formation by merging multiple trapped Bose-Einstein condensates Chad Weiler, Tyler Neely, David Scherer, Brian Anderson We have experimentally studied the merging of three trapped Bose-Einstein condensates. We find that, depending on the rate of merging, the final single BEC may contain a single vortex core (for slow merging rates), or multiple cores (for fast merging rates). Similarly, a triple-well trap may initiate the formation of three isolated BECs, but if the barriers between the wells are weak enough, the condensates merge together during their growth; this process can also lead to the formation of vortices in the final BEC. We interpret both scenarios in terms of interference between the initial uncorrelated condensates with indeterminate relative phases. We will discuss the results and interpretation of this experiment (D.R. Scherer, C.N. Weiler, T.W. Neely, B.P. Anderson, cond-mat/0610187, to be published in Phys. Rev. Lett.). [Preview Abstract] |
Wednesday, June 6, 2007 11:18AM - 11:30AM |
B4.00005: Spontaneous vortex formation during the creation of Bose-Einstein condensates Brian Anderson, Chad Weiler, Tyler Neely, David Scherer We have experimentally observed spontaneous generation and trapping of quantized vortices in single-component Bose- Einstein condensates. The BECs were created by a standard evaporative cooling procedure in a magnetic trap, without any additional methods of intentionally imparting angular momentum to the trapped atoms. After each BEC was formed, it was expanded such that the presence or absence of a vortex was determined. By observing numerous condensates, the statistical dependence of vortex formation on trapping and cooling parameters was examined. We will describe our experimental results and our interpretation of the vortex formation mechanism. [Preview Abstract] |
Wednesday, June 6, 2007 11:30AM - 11:42AM |
B4.00006: Collective Excitations of Pinned Vortex Lattice of a Rotating Condensate Han Pu, Leslie Baksmaty, Nicholas Bigelow Using state-of-the-art numerical procedures, we have calculated collective excitation spectrum of the vortex lattice state of a rotating atomic condensate subject to a co-rotating periodic pinning potential. The presence of pinning changes the structure of the excitation spectrum dramatically compared with an unpinned lattice. We have also studied the quantum depletion of the normal modes and its relation to the structure phase transition of the vortex lattice. [Preview Abstract] |
Wednesday, June 6, 2007 11:42AM - 11:54AM |
B4.00007: Signatures of Quantized Vortex States in Rotating Optical Lattices Brandon Peden, Rajiv Bhat, Meret Kr\"{a}mer, Murray Holland Recent theoretical studies of ultracold gases in two-dimensional rotating optical lattices have taken advantage of the notion of quasi-angular momentum, a quantum number that characterizes the eigenstates of a system with a discrete rotational symmetry. In a gas of strongly interacting bosons, transitions between states of differing quasi-angular momentum have been predicted, implying the entrance of vortices to the lattice. We identify signatures in the linear momentum distribution that distinguish between the different quasi-angular momentum states. [Preview Abstract] |
Wednesday, June 6, 2007 11:54AM - 12:06PM |
B4.00008: Observation of Phase Defects of a quasi-2D BEC in a Single Dipole Trap Pierre Clade, Changhyun Ryu, Anand Ramanathan, Kristian Helmerson, William Phillips At finite temperature, in a homogeneous two dimensional bosonic gas, long range order is destroyed by thermal fluctuations. For interacting atoms, below a critical temperature, the gas is a superfluid with phase defects consisting of pairs of vortex-antivortex; above this temperature, when the pairs are unbound, the gas enters a normal phase. The nature of the superfluid transition in a non-homogeneous trapped gas has been a topic of some debate. We are studying sodium atoms in a single quasi-2D optical trap. This trap is formed by an elliptical red detuned laser beam and has an aspect ratio of 40. We image the single ``pancake'' from both sides and observe density fluctuations with time of flight as well as phase fluctuations using Bragg interferometry techniques. Preliminary results provide evidence of the formation of vortex-antivortex pairs in this system. [Preview Abstract] |
Wednesday, June 6, 2007 12:06PM - 12:18PM |
B4.00009: Use of custom potentials to facilitate access to quantum Hall states in rotating Bose gases Alexis Morris, David Feder Through the use of exact diagonalization, we have numerically investigated the properties of zero-temperature, harmonically trapped, rotating ultracold Bose gases. For small number of alkali atoms, we consider the case of tight confinement along the axial direction such that the atoms are essentially two-dimensional. As the rotation rate is increased, the interacting Bose gas undergoes a series of transitions from one quantum Hall state to another akin to what is seen in a two-dimensional electron gas subjected to a strong perpendicular magnetic field. Unlike the electronic case, experimental verification of the existence of quantum Hall states in rotating Bose gases has not yet been achieved. To remedy this, we have investigated the possibility of adding custom built potentials to the existing trapping potential such that experimental access to specific quantum Hall states is facilitated. We find that the creation of certain quantum Hall states in rotating Bose gases should be feasible using current experimental capabilities. (Research supported by NSERC, iCORE and CFI) [Preview Abstract] |
Wednesday, June 6, 2007 12:18PM - 12:30PM |
B4.00010: Quantum phase transitions, symmetry breaking, and the Goldstone mode in metastable Bose-Einstein condensates Rina Kanamoto, Lincoln Carr, Masahito Ueda It is widely believed that the circulation in a repulsive superfluid system is quantized and that there is a discontinuous jump in states between different values of the circulation. We point out that this rule applies only to the ground state, and that continuous transitions between different values of the circulation do occur for metastable states of repulsive Bose-Einstein condensates on a ring. The key to these continuous transitions is the emergence of a dark or grey soliton train that carries a non-integer portion of the circulation. Mean-field theory shows that these continuous changes can be classified as second-order quantum phase transitions between metastable states, where quantized rotation and the soliton state are associated with bifurcations of metastable solutions. We also investigate this problem using quantum field theory, where the broken-symmetry solution and appearance of the Goldstone mode are described by a linear superposition of the quasidegenerate eigenstates of the many-body Hamiltonian. [Preview Abstract] |
Wednesday, June 6, 2007 12:30PM - 12:42PM |
B4.00011: ABSTRACT WITHDRAWN |
Wednesday, June 6, 2007 12:42PM - 12:54PM |
B4.00012: Nonlocal stabilization of nonlinear beams in a self-focusing atomic vapor Mark Saffman, Stefan Skupin, Wieslaw Krolikowski We show that ballistic transport of optically excited atoms in a hot atomic vapor provides a nonlocal nonlinearity which stabilizes the propagation of vortex beams and higher order modes in the presence of a self-focusing nonlinearity. Numerical experiments demonstrate stable propagation of lowest and higher order vortices over a hundred diffraction lengths, before dissipation leads to decay of these structures. [Preview Abstract] |
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