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 W4: Bose-Einstein Condensates |
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Chair: J. Bohn, University of Colorado Room: TELUS Convention Centre Macleod A1-A2 |
Saturday, June 9, 2007 8:00AM - 8:12AM |
W4.00001: ABSTRACT WITHDRAWN |
Saturday, June 9, 2007 8:12AM - 8:24AM |
W4.00002: Evolution of Spin Textures in a Spinor Bose Einstein Condensate Jennie Guzman, Mukund Vengalattore, Sabrina Leslie, Dan Stamper-Kurn We study the evolution of spin textures in a F=1 spinor Bose Einstein condensate of $^{87}$Rb atoms. We do so by allowing the magnetization profile of the condensate to evolve in an inhomogeneous magnetic field. Utilizing in-situ magnetization sensitive imaging, we spatially and temporally resolve the resulting vector magnetization profile. These experiments are performed at low quadratic Zeeman shift where a $^{87}$Rb condensate is known to be ferromagnetic. [Preview Abstract] |
Saturday, June 9, 2007 8:24AM - 8:36AM |
W4.00003: ABSTRACT WITHDRAWN |
Saturday, June 9, 2007 8:36AM - 8:48AM |
W4.00004: Soliton-soliton interaction in F=1 spinor Bose-Einstein condensates Takahiko Miyakawa, Hiroyuki Abe, Yuko Fukuyo We consider a cold atomic gas with hyperfine spin F=1 at zero temperature. It was found that the multi-component Gross- Pitaevskii equations describing the dynamics of a spinor Bose- Einstein condensate in one dimension have one soliton solution. We derive an exact expression for two-soliton solution in order to investigate spin dependent forces among solitons. We also examine soliton-soliton collisions and show some aspects of the spin mixing dynamics and bound state formation in low-energy collisions. [Preview Abstract] |
Saturday, June 9, 2007 8:48AM - 9:00AM |
W4.00005: Observation of phase-fluctuating one-dimensional Bose-Einstein condensates Nicolaas van Druten, Aaldert van Amerongen, Jan-Joris van Es, Philipp Wicke The one-dimensional Bose gas is predicted to exhibit a rich variety of different quantum regimes. We experimentally study the properties of an elongated Bose-Einstein condensate crossing over from the three-dimensional into the one- dimensional regime. We reach extreme aspect ratios up to 400 of the needle shaped condensates using micron sized patterns on a chip. To probe the atomic velocity distribution in the elongated dilute cloud we focus the atoms along the long axis using a harmonic potential pulse. In the focus the initial velocities are mapped to a spatial distribution. This is a powerful technique that allows characterization of individual small, low-density clouds. Phase fluctuations stemming from elementary excitations along the axis of the elongated condensate are observed as density fluctuations in time-of- flight. These may provide the possibility of (noise) thermometry far below the condensation temperature. [Preview Abstract] |
Saturday, June 9, 2007 9:00AM - 9:12AM |
W4.00006: Critical behavior of a trapped interacting Bose gas Stephan Ritter, Tobias Donner, Thomas Bourdel, Ferdinand Brennecke, Anton \"Ottl, Michael K\"ohl, Tilman Esslinger In the vicinity of a phase transition minute variations in the controlling parameters can dramatically change the properties of a system. Using a trapped Bose gas we have entered the critical regime of Bose-Einstein condensation and gained access to its beyond mean-field physics. This regime is characterized by fluctuations extending far beyond the thermal de Broglie wavelength: The length scale over which the system behaves coherently diverges, which is directly reflected in the shape of the spatial first order correlation function. Using matter-wave interference we measure the correlation length of these fluctuations as a function of temperature. We study the divergence of the correlation length of the order parameter as the temperature approaches the critical point and determine its critical exponent for a trapped, weakly interacting Bose gas to be $\nu=0.67\pm0.13$. [Preview Abstract] |
Saturday, June 9, 2007 9:12AM - 9:24AM |
W4.00007: Observation of Faraday Waves in a Bose-Einstein Condensate Peter Engels, Collin Atherton, Mark Hoefer Faraday waves in a cigar-shaped Bose-Einstein condensate are created. It is shown that periodically modulating the transverse confinement, and thus the nonlinear interactions in the BEC, excites small amplitude longitudinal oscillations through a parametric resonance. It is also demonstrated that even without the presence of a continuous drive, an initial transverse breathing mode excitation of the condensate leads to spontaneous pattern formation in the longitudinal direction. Finally, the effects of strongly driving the transverse breathing mode with large amplitude are investigated. In this case, impact-oscillator behavior and intriguing nonlinear dynamics, including the gradual emergence of multiple longitudinal modes, are observed. [Preview Abstract] |
Saturday, June 9, 2007 9:24AM - 9:36AM |
W4.00008: Chaotic escape dynamics of ultracold and Bose-condensed atoms Kevin Mitchell, Daniel A. Steck We consider the nonlinear dynamics of small packets of ultra-cold and Bose-condensed atoms in a two-dimensional, double-well optical trap, composed of two overlapping Gaussian beams. We are interested in the transport of such packets from one side of the well to the other, and potential escape from the trap. We theoretically investigate how the time-dependent escape rate of atoms from the trap is influenced by the chaotic dynamics of the potential and by the inherent nonlinearity induced by atom-atom interactions. [Preview Abstract] |
Saturday, June 9, 2007 9:36AM - 9:48AM |
W4.00009: Modeling the Expansion of Bose--Einstein Condensate Mixtures in the Thomas--Fermi Limit Mark Edwards, Laura Halmo, Charles Holcombe We have studied the expansion of a mixture of $^{85}$Rb--$^{87} $Rb Bose--Einstein condensates within the Thomas--Fermi approximation. Systems involving mixtures of Bose--Einstein condensates of different atomic species can be accurately modeled by coupled Gross--Pitaevskii equations. As for single condensates, the coupled Gross--Pitaevskii equations can be written in hydrodynamic form where each condensate is described by a density and phase. Also just as for single condensates, the hydrodynamic equations of motion for condensate mixtures reduce to classical equations of motion when their quantum pressure terms are neglected (Thomas--Fermi approximation). In this case, it is possible to find time--dependent Thomas--Fermi approximate solutions for the hydrodynamic equations of motion for mixtures. We present these equations and their solution for the particular case of a $^{85}$Rb--$^{87}$Rb expansion that occured in a recent experiment performed in the Jin group at JILA. We also highlight interesting features that can occur because of interaction effects in the expansion of multiple-- condensate mixtures. [Preview Abstract] |
Saturday, June 9, 2007 9:48AM - 10:00AM |
W4.00010: A Bose-Einstein Condensate Level Satyan Bhongale, Eddy Timmermans We consider a trapped, phase separated two-component or two-species Bose-Einstein condensate (BEC) system: a large BEC of bosonic atoms of type `a' in which a smaller bubble of a BEC of `b' atoms is immersed. If the trapping force of BEC a is tuned near the value at which it nearly cancels the buoyancy force experienced by the immersed BEC- b fluid, the equilibrium center-of mass position of the BEC- b bubble becomes highly sensitive to any force difference experienced by the a and b atoms. Imaging the position of the BEC-b bubble than gives a sensitive measure of the external force. If the cancellation is nearly complete, the equilibrium position of the nearly freely floating BEC-b bubble can be used to study the Casimir-like forces generated by the quantum fluctuations of he finite size BEC-system. [Preview Abstract] |
Saturday, June 9, 2007 10:00AM - 10:12AM |
W4.00011: Calculation of $g_2$ for a Finite Temperature Gas Alice Bezett, Emese Toth, Blair Blakie The landmark experiment done by Hanbury-Brown and Twiss (HBT) in 1956 has seen a renewal of interest in application to ultra-cold gases. It has long been desired that the HBT effect, that is, correlations between photons from a thermal source, be verified for bosonic atoms from a thermal cloud. There is a prohibitively small probability of observing a many-particle correlation effect in a conventional particle beam, and for this reason laser cooling and a combination of laser and evaporative cooling are employed in studies of particle correlations. We present a finite temperature theoretical model for calculating correlations in degenerate Bose gas that systematically includes the effects of harmonic trap confinement, interactions between the particles and is valid in the critical regime. This model is based on the non-pertubative Projected Gross Pitaevskii (PGPE) formalism, which includes the dynamics of the low lying modes of the thermal cloud, coupled to a semiclassical description of high the energy modes. We discuss results of these simulations for a three dimensional cloud of ultra-cold bosons at a range of temperatures below $T_c$. [Preview Abstract] |
Saturday, June 9, 2007 10:12AM - 10:24AM |
W4.00012: Radial and angular rotons in trapped dipolar gases Shai Ronen, Daniele Bortolotti, John Bohn We study Bose-Einstein condensates with purely dipolar interactions in oblate (pancake) traps. We find that the condensate always becomes unstable to collapse when the number of particles is sufficiently large. We analyze the instability, and find that it is the trapped-gas analogue of the ``roton- maxon'' instability previously reported for a gas that is unconfined in two dimensions. In addition, we find that under certain circumstances, the condensate wave function attains a biconcave shape (like a red-blood cell), with its maximum density away from the center of the gas. These biconcave condensates become unstable due to azimuthal excitation - an angular roton. [Preview Abstract] |
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