Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session H36: BEC and Trapped Bose Gases |
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Sponsoring Units: DAMOP Chair: Dan Stamper-Kurn, UC-Berkeley Room: Convention Center 510 |
Tuesday, March 22, 2005 8:00AM - 8:12AM |
H36.00001: Ring Dark Solitons in Bose-Einstein Condensates Bryan Nelsen, Mark Edwards, Lincoln Carr, Charles W. Clark The time--independent Gross--Pitaevskii equation describing a Bose--Einstein condensate confined in a cylindrical box admits ``ring solutions.''$^{1}$ These solutions consist of a central vortex line surrounded by concentric nodal rings. We have studied the time evolution of ring solutions having one node between the vortex line at $\rho=0$ and the box wall and which have had a phase mask placed across the node. This phase gradient mimics the phase jump exhibited by a dark soliton in motion. Our study has been carried out by solving the time-- dependent Gross--Pitaevskii equation using a Crank--Nicolson propagator. The initial conditions were generated using a shooting algorithm that needed a power series solution of the time--independent Gross--Pitaevskii equation to find the solution away from the singularity at the vortex line. We find that, in general, these systems behave like dark or gray solitons where the node exhibits radial oscillations. We shall present results for various phase gradients and winding numbers and comment on the possibility of observing these phenomena in laboratory Bose--Einstein condensates.\\ \ \\ $^{1}$L.D.\ Carr and C.W.\ Clark, cond--mat/0408460 [Preview Abstract] |
Tuesday, March 22, 2005 8:12AM - 8:24AM |
H36.00002: Experiments with Ultracold Atoms in an Optical Cavity Subhadeep Gupta, Kevin Moore, Thomas Purdy, Kater Murch, Stefan Schmid, Dan Stamper-Kurn Magnetically-trapped ultracold atoms provide a robust, long-lived atomic source for many-atom cavity QED.~We have developed a system which is capable of placing a large ensemble of $^{87}$Rb atoms within the confines of a high finesse optical cavity. Recent experimental progress will be discussed. [Preview Abstract] |
Tuesday, March 22, 2005 8:24AM - 8:36AM |
H36.00003: BEC in a novel magnetic trap for many-atom cavity QED Kevin Moore, Kater Murch, Thomas Purdy, Subhadeep Gupta, Dan Stamper-Kurn We have produced a Rb-87 BEC in novel mm-scale Ioffe-Pritchard trap. The trap is designed to interface with a high finesse optical cavity with the goal of performing cavity QED with ultracold atomic samples. Performance of the trap and recent experimental progress will be discussed. [Preview Abstract] |
Tuesday, March 22, 2005 8:36AM - 8:48AM |
H36.00004: Exact Calculations for Ultracold Rotating Bose Gases Alexis Gagnon Morris, David Feder Through the use of exact diagonalization, we have investigated general properties of harmonically trapped, rotating ultracold bose gases having both attractive and repulsive interactions. We have calculated the low energy spectrum for a small number of bosons and have used the similarities between fermions in a strong magnetic field and bosons subjected to rotation in order to identify different bosonic fractional quantum states which may be used to perform topological quantum computations. [Preview Abstract] |
Tuesday, March 22, 2005 8:48AM - 9:00AM |
H36.00005: Nambu-Goldstone Mode in a Rotating Dilute Bose-Einstein Condensate Tatsuya Nakajima, Masahito Ueda The Nambu-Goldstone mode associated with vortex nucleation in a harmonically confined, two-dimensional dilute Bose-Einstein condensate is identified to be the lowest-lying envelope of a series of octupole-mode branches that are shifted one by one by an additional quadrupole-mode excitation. As the vortex reaches the center of the condensate and becomes stabilized, the Nambu- Goldstone mode is found to acquire mass due to its coupling to higher rotational bands. [Preview Abstract] |
Tuesday, March 22, 2005 9:00AM - 9:12AM |
H36.00006: Pinning of vortices in a Bose-Einstein condensate by an optical lattice J.W. Reijnders, R.A. Duine We consider the ground state of vortices in a Bose-Einstein condensate. We show that turning on a weak optical periodic potential leads to a transition from the triangular Abrikosov vortex lattice to phases where the vortices are pinned by the optical potential. We discuss the phase diagram of the system for a two-dimensional optical periodic potential with one vortex per optical lattice cell. We also discuss the influence of a one-dimensional optical periodic potential on the vortex ground state. The latter situation has no analogue in other condensed-matter systems. [Preview Abstract] |
Tuesday, March 22, 2005 9:12AM - 9:24AM |
H36.00007: Quantum Theory of LLL Cold-Atom Vortices C.B. Hanna, A.J. Sup, A.H. MacDonald In the lowest-Landau-level (LLL) approximation, interacting bosons can be described without further approximation in terms of vortex positions. We report on the quantum theory of LLL vortices in trapped cold-atom systems. For this system, the harmonic theory of vibrating vortices is equivalent to the Bogoliubov theory of weakly interacting cold atoms. We find that a proper description of the vortex system requires the inclusion of invisible vortices located outside the high-atomic density region of the atom cloud. The vortex degrees of freedom have non-local commutation relations, which leads to kinetic vortex-vortex coupling in the semi-classical equations of motion. The excitation spectrum includes collective vortex vibrations and single-particle excitations, and a low-energy ``zero mode'' whose energy vanishes for a trap with perfect circular symmetry. We discuss the effects of small trap asymmetry on this zero mode, and calculate its influence on quantum fluctuations within the Bogoliubov approximation. [Preview Abstract] |
Tuesday, March 22, 2005 9:24AM - 9:36AM |
H36.00008: Density profiles for atomic quantum Hall states Frank van Lankvelt, Nigel Cooper, Jasper Reijnders, Kareljan Schoutens Among the fascinating developments in the field of quantum gases is the possibility to study correlated states of matter in a setting that is entirely different from the traditional setting of electrons in a solid state environment. A prime example are fractional quantum Hall (qH) states, which are expected when trapped atoms are made to rotate at ultra-high angular momentum. The most direct experimental signature of electronic (fractional) qH states, the quantization of the Hall conductance, is not easily available for realizations of such states with neutral atoms. Therefore, we need to find other signatures that arise from their presence. We will show what effect these states have on the density in a variety of regimes and in particular discuss the fate of (weakly) coupled layers of rotating Bose gases. [Preview Abstract] |
Tuesday, March 22, 2005 9:36AM - 9:48AM |
H36.00009: Drag effects and vortex states in binary superfluids in optical lattices Alexander Meyerovich, Anatoly Kuklov Drag effects in two-condensate superfluids (A and B) in optical lattices are explored in strongly interacting limit. Mutual drag changes circulation quanta of vortices depending on the component concentration and interaction. This is a lattice analog of $^{3}$He-HeII mixtures, in which the drag, proportional to the difference between bare and effective masses of quasiparticles, causes pressure-driven transitions in vortex charges [1]. The vortex binding in the hard-core boson limit relies, in contrast to the soft-core case studied in Monte Carlo simulations [2], on the vacancy-assisted tunneling. The model lattice for study of such effects is introduced. The variational and Monte Carlo calculations for the system, in which the tunneling for component A depends on the concentration of B, show the possibility of formation of the quasi-molecular condensate AB$_{m}$ in addition to the condensates of A and B. A strong drag, leading to the composite vortices with multiple quanta, also becomes possible. The work is supported by NSF grants DMR-0077266 and ITR\textbf{-}405460001 and PSC-CUNY- 665560035. 1. A. E. Meyerovich, Phys. Rev. A \textbf{68}, 05162 (2003); Sov. Phys.-JETP \textbf{60}, 41 (1984) 2. A. Kuklov, N. Prokof'ev, and B. Svistunov, Phys. Rev. Lett. \textbf{92}, 030403 (2004) [Preview Abstract] |
Tuesday, March 22, 2005 9:48AM - 10:00AM |
H36.00010: Real-time imaging of spinor dynamics in $^{87}$Rb Bose Einstein Condensates Sabrina R. Leslie, Lorraine Sadler, James Higbie, Shin Inouye, Ananth Chikkatur, Dan M. Stamper-Kurn We investigate spinor dynamics in a F=1 ferromagnetic $^{87}$Rb Bose Einstein Condensate, measured in real time. Previous work has used single-shot absorption imaging to determine the ferromagnetic nature of $^{87}$Rb. In contrast, we probe the system using non-destructive polarization-sensitive imaging, allowing us to spatially resolve and characterize both the longitudinal and transverse magnetization of a spinor wavefunction. Recent progress toward observation of spontaneous magnetization will be reported. [Preview Abstract] |
Tuesday, March 22, 2005 10:00AM - 10:12AM |
H36.00011: Quantum Chaos of Bogoliubov Waves for a Bose-Einstein Condensate in Stadium Chuanwei Zhang, Jie Liu, Mark Raizen, Qian Niu We investigate the possibility of quantum (or wave) chaos for the Bogoliubov excitations of a Bose-Einstein condensate in billiards. Because of the mean field interaction in the condensate, the Bogoliubov excitations are very different from the single particle excitations in a non-interacting system. Nevertheless, we predict that the statistical distribution of level spacings is unchanged by mapping the non-Hermitian Bogoliubov operator to a real symmetric matrix. We numerically test our prediction by using a phase shift method for calculating the excitation energies. [Preview Abstract] |
Tuesday, March 22, 2005 10:12AM - 10:24AM |
H36.00012: Bose-Einstein condensation with attractive interactions Asaad Sakhel, Jonathan Dubois, Henry Glyde We investigate 20 Bosons in a tight harmonic trap using quantum Monte Carlo methods. The Bosons interact via a pair potential that has a repulsive hard core plus an attractive square well leading to a negative scattering length. The total energy, Boson distribution in the trap, condensate fraction, condensate distribution in the trap and other properties are evaluated as a function of the attractive well depth (scattering length). In the weak attraction (dilute) limit, the Monte Carlo energies agree well with those calculated using the Gross-Pitaevskii (GP) equation. We also find a sharp increase in density in the regime where the GP equation predicts collapse. At the GP ``collapse" point, we find a gas to liquid transition to a liquid density and energy that saturates to fixed values as the scattering length is increased. The liquid density depends on the HC diameter and the Range of potential. At the liquid densities, the scattering length is no longer a good representation of the potential. The condensate fraction depends chiefly on the hard core part of the potential. There can be substantial depletion of the condensate (e.g. 50 percent) and its value is qualitatively predicted by the Bogoliubov expression if the hard core diameter is used (rather than the scattering length). [Preview Abstract] |
Tuesday, March 22, 2005 10:24AM - 10:36AM |
H36.00013: The ground state of Bose gases with repulsive interaction: A quantum Monte Carlo study Wirawan Purwanto, Shiwei Zhang The capability of Feshbach resonances to experimentally tune the atomic interaction in trapped gases provides a rich opportunity to better understand the properties of strongly-correlated systems. We report results from many-body ground-state calculations of interacting Bose gases in 3D with repulsive interactions. We characterize the effect of many-body correlations as a function of atom-atom scattering length $a_s$. Calculations were done for both trapped atomic gases and bulk fluids at different densities. We use a recently developed Quantum Monte Carlo method\footnote{Phys. Rev. E 70, 056702 (2004)}, which gives a very good approximation to the true ground state. We put the bosons on a discrete mesh and model the interatomic interaction by an on-site, $\delta$-function potential parametrized by $a_s$. Results will be presented for the energetics, density profile, momentum distribution, condensate fraction, and correlation functions. We analyze the deviations of the standard Gross-Pitaevskii and Bogoliubov approaches from our results as the system becomes more strongly interacting, and discuss their implications. [Preview Abstract] |
Tuesday, March 22, 2005 10:36AM - 10:48AM |
H36.00014: Ab initio study of polar molecules in an optical lattice Svetlana Kotochigova, Eite Tiesinga The emerging field of trapping ultracold polar molecules in an optical lattice opens prospects for new physics, chemistry, and quantum computations. The ultimate goal of our study is to provide information needed to achieve control at the quantum level over internal and external degrees of freedom of a polar molecule in an optical lattice. Here we report data concerning polar RbCs molecules. This data includes relativistic electronic potentials, permanent and transition dipole moments, the ground-state molecular dynamic polarizability as function of the internuclear separation, and Franck-Condon factors between vibrational levels of ground and exited states, which are needed to design an optimal optical lattice. We also study interactions between polar RbCs molecules confined in different lattice sites. Theoretical tools include the relativistic multiconfiguration valence bond method for the electronic structure and a discrete variable representation method for the vibrational motion. [Preview Abstract] |
Tuesday, March 22, 2005 10:48AM - 11:00AM |
H36.00015: Bose-Einstein Condensation in Trapped Dipolar Gases Kwangsik Nho, D.P. Landau Using path integral Monte Carlo simulation methods[1], we have studied the equilibrium properties of harmonically trapped atomic condensates with long-range dipole-dipole interactions in addition to the usual short-range s-wave interactions. The recent observation of Bose-Einstein condensation of molecules has renewed interest in the investigation of quantum gases with dipolar interactions[2]. We have calculated the energetics and structural properties such as the total density profiles, the condensate density profiles, and the condensate fraction for various values of the number of atoms, dipolar moment, and the trap aspect ratio as a function of temperature. We found that the sign and the value of the dipole-dipole interaction energy depend on the trapping geometry. For a disk-shaped trap, the net effect of interactions is repulsive and the condensate expands with respect to that without long-range interactions along the radial direction. For dipoles oriented along the axis of a cylindrical trap we have found shrinking of the condensate due to the attractive dipolar interaction. \\ \newline \noindent *Research supported by NASA\\ \noindent [1] K. Nho and D. P. Landau, Phys. Rev. A. {\bf 70}, 53614 (2004).\\ \noindent [2] M. Greiner, C. A. Regal, and D.S. Jin, Nature {\bf 426}, 537 (2003); S. Jochim {\it et al.}, Science {\bf 302}, 2101 (2003); M. W. Zwierlein {\it et al.}, Phys. Rev. Lett. {\bf 91}, 250401 (2003). [Preview Abstract] |
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H36.00016: Interference of Rotating Atomic Clouds Erich Mueller, Tin-Lun Ho We study the theory of interference between spinning clouds of ultracold atoms; quantifying how intermeshed vortices in two displaced clouds form intricate patterns when the clouds are overlapped. These patterns, dominated by stripes, can be imaged in circumstances where individual vortices cannot be resolved. We contrast these structures (which were recently observed at JILA [Schweikhard et al. Phys. Rev. Lett. 93, 210403 (2003)]) with the ones which will be seen during the interference of two atomic clouds in highly correlated quantum Hall states. The striking differences in these interference patterns allows one to distinguish coherent and correlated states. [Preview Abstract] |
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