Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session W32: BoseEinstein Condensation in Trapped Atomic Gases 
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Sponsoring Units: DAMOP Chair: Murray Holland, University of Colorado Room: Colorado Convention Center 402 

W32.00001: ABSTRACT WITHDRAWN 
Thursday, March 8, 2007 2:42PM  2:54PM 
W32.00002: Collective Excitations of a TwoComponent Bose Condensate at Finite Temperature Changhua Zhang, Herbert A. Fertig We compare the collective modes for Bosecondensed systems with two degenerate components with and without intercomponent coherence at finite temperature using the timedependent HartreeFock approximation. We show that the interaction between the condensate and noncondensate in these two cases results in qualitatively different collective excitation spectra. We show that at zero temperature the singleparticle excitations of the incoherent Bose condensate can be probed by intercomponent excitations. [Preview Abstract] 
Thursday, March 8, 2007 2:54PM  3:06PM 
W32.00003: ABSTRACT HAS BEEN MOVED TO B21.00008 
Thursday, March 8, 2007 3:06PM  3:18PM 
W32.00004: Dispersive Shock Wave Collisions in BoseEinstein Condensates and Light Mark Hoefer, Mark Ablowitz When two classical shock waves collide, the interaction is relatively simple and is explained by classical hyperbolic system theory and jump/entropy conditions. An analogous theory for the interaction of two dispersive shock waves (DSWs) is presented. Two cases will be considered: i) a collision where two DSWs are propagating directly toward one another, ii) merging where a faster DSW overtakes a slower one. It is shown that, after a complicated quasiperiodic or multiphase region is created, the DSW interaction process results in: i) two single DSWs propagating away from one another in the collision case, ii) a single, larger DSW representing the merger of the original two DSWs in the merging case. Remarkably, these results coincide exactly with their classical shock wave counterpart. These results have direct application to BoseEinstein condensates and nonlinear optics. [Preview Abstract] 
Thursday, March 8, 2007 3:18PM  3:30PM 
W32.00005: Effects of Disorder on a BoseEinstein Condensate with Tunable Interaction: Transition to an Insulator and Loss of Phase Coherence$^1$ Yong P. Chen, J. Hitchcock, D. Dries, M. Junker, C. Welford, R.G. Hulet We report our study of the effects of disorder on a BoseEinstein condensate (BEC) of $^7$Li atoms with tunable interaction. A large $^7$Li BEC is created in an elongated optical trap after forced evaporation. The strength of the repulsive interaction is tuned using a magnetic Feshbach resonance. A disordered optical potential, whose strength is also tunable, is generated by projecting a laser speckle pattern onto the atoms. We have performed transport studies by measuring the center of mass motion of the trapped BEC in the presence of disorder. Beyond a disorder strength ($V_t$), the dipole oscillation of the superfluid BEC is completely suppressed, signaling a transition to an insulator. We have also studied the time of flight expansion of the BEC after release from the trap and disordered potentials. With intermediate disorder strengths, striking fringes appear in the cloud after sufficient expansion time. Beyond some disorder strength ($V_p$), comparable to the chemical potential of the trapped BEC, the fringes are washed out, signaling a loss of phase coherence. Interestingly, $V_p$ is significantly larger than $V_t$, suggesting that finite phase coherence can still exist in the insulator. [Preview Abstract] 
Thursday, March 8, 2007 3:30PM  3:42PM 
W32.00006: Quantum Accelerator Modes in BEC Vijayashankar Ramareddy, Ghazal BehinAein, Peyman Ahmadi, Gil Summy The quantum delta kicked accelerator can be realized by subjecting cold atoms to spatially corrugated off resonant pulses of light. These standing wave pulses are applied in the direction in which there is a component of gravity and result in acceleration of a group of atoms. For the first time we observed Quantum Accelerator Modes (QAM) in BEC. We show that using the narrow momentum distribution of BEC, the structures in phase space map produced by a psuedo classical theory can be directly studied. We show that QAMs can be effeciently populated using BEC. Details will be presented. [Preview Abstract] 
Thursday, March 8, 2007 3:42PM  3:54PM 
W32.00007: Density Profiles of $^{85}$Rb$^{87}$Rb Binary Mixtures Laura Halmo, Alison Lota, Mark Edwards, Scott Papp, Deborah Jin We have studied the density distribution of binary mixtures of $^{87}$Rb and $^{85}$Rb BoseEinstein condensates under conditions similar to a recent experiment conducted in the Jin Group at JILA. In this experiment, a binary mixture of the two Rb isotopes were confined in a magnetic trap and rf evaporative cooling was carried out on the $^{87}$Rb causing sympathetic cooling of the $^{85}$Rb. This mixture was then transferred to an optical trap to minimize $^{85}$Rb 3body loss and condensation was achieved by slowly decreasing the depth of the optical trap. An external magnetic field using a Feshbach resonance enabled tuning of the 8585 scattering length. Density profiles were obtained by taking absorption images of expanded condensates after releasing them from the trap. We have calculated the theoretical shape of such images by solving approximately the coupled timedependent (TD) GrossPitaevskii (GP) equations. As initial states we used ThomasFermi approximate solutions of the timeindependent GP equation and approximately solved the timedependent GrossPitaevskii equation to model the expansion. We present a comparison of this calcualation with the experimental data. [Preview Abstract] 
Thursday, March 8, 2007 3:54PM  4:06PM 
W32.00008: BoseEinstein S=1 Spinor Condensates, Dynamics, Noise Statistics and Scaling George I. Mias, Steven M. Girvin We examine BoseEinstein spinor condensates in the shorttime nonlinear regime for S=1 atoms in the context of $^{87}$Rb studied experimentally by the StamperKurn group [L. Sadler et al, Nature {\bf 443}, p193, 2006]. We will describe the quantum dynamics of a sample that starts as a condensate of $N$ atoms in a pure $S=1$, $m_f=0$ state. Our approach seeks to improve the meanfield description of such systems by including the contributions of quantum fluctuations that seed the eventual formation of ferromagnetic domains. We will give a simple quantum description of the system for the shorttime regime in analogy with ``twomode squeezing" of quantum optics, treating the initial $m_f=0$ condensate as a source for the conversion to pairs of $m_f=1,1$ states. Even though the system as a whole is described by a pure state with zero entropy, the reduced density matrix for the $m_f=+1$ degree of freedom, obtained by tracing out the $m_f=1,0$ degrees of freedom, is a thermal state. We propose to observe the large fluctuations associated with this thermal state using HanburyBrownTwiss noise correlation measurements in the density and momentum distributions of the individual $m_f$ species. Finally, we will discuss the effect of excitations in connection to the seeding and ultimate formation of domains of ferromagnetically aligned spins. (Supported by NSF DMR0603369). [Preview Abstract] 
Thursday, March 8, 2007 4:06PM  4:18PM 
W32.00009: Nonlinear quantum hydrodynamics in BoseEinstein condensates Peter Engels, Collin Atherton BoseEinstein condensates are quantum fluids governed by nonlinear interatomic interactions. They provide an excellent tool to study intriguing phenomena in the field of nonlinear hydrodynamics. We will report on hydrodynamics experiments carried out in a newly constructed BEC apparatus at Washington State University, Pullman. Current research directions include quantum shock waves and parametric resonances. We will describe the current results and future directions. [Preview Abstract] 
Thursday, March 8, 2007 4:18PM  4:30PM 
W32.00010: Quantum Field Theoretical Description of Dynamical Instability of Trapped BoseEinstein Condensates Makoto Mine, Masahiko Okumura, Tomoka Sunaga, Yoshiya Yamanaka The Bogoiubovde Gennes equations are used for a number of theoretical works on the trapped BoseEinsetein condensates. Particularly, it is important that if all of the eigenvalues of the equations are real, the solutions of the equations diagonalize the unperturbed Hamiltonian, and the quasiparticle picture, which describes the quantum fluctuation around the condensates, is obtained. We consider the quantum fluctuation in the case that these equations have complex eigenvalues. First, to expand quantum field which represents the quantum fluctuation, we give the complete set including pairs of complex modes whose eigenvalues are complex conjugate to each other. The expansion of the quantum field brings the operators associated with the complex modes, which are simply neither bosonic nor fermionic ones. Next, to evaluate physical quantities, we construct the eigenstate of the complex mode sector of the unperturbed Hamiltonian. Finally, we discuss the instability of the condensates caused by the quantum fluctuation associated with the complex mode in the context of Kubo's linear response theory. [Preview Abstract] 
Thursday, March 8, 2007 4:30PM  4:42PM 
W32.00011: Conversion efficiency of heteronuclear Feshbach molecules Shohei Watabe, James E. Williams, Tetsuro Nikuni We study formations of heteronuclear Feshbach molecule in population imbalanced atomic gases, extending the recent work [J. E. Williams et. al., New J. Phys. 8, 150 (2006)] on the Feshbach molecule formation. We find that conversion efficiency depends on a ratio of the number of atomic species in the initial state before the magnetic sweep, as well as an initial temperature and an initial peak phase space density. At low temperature in quantum degenerate regime, quantum statistics of atoms plays an important role in conversion efficiencies. Maximum conversion efficiencies are determined by quantum statistics and the number ratio. When the major component is bosonic, the maximum conversion efficiency is $50\%$. On the other hand, when the major component is fermionic and the minor component is bosonic, the maximum conversion efficiency has a range from $50\%$ to $100\%$, which is determined by the initial atomic ratio. In the case that both components are fermionic, the maximum conversion efficiency is $100\%$. In the region where the gases does not condense, the conversion efficiency is described as a function of initial peak phase space density of a major component. [Preview Abstract] 
Thursday, March 8, 2007 4:42PM  4:54PM 
W32.00012: Using modified Gaussian distribution to study the physical properties of one and twocomponent ultracold atoms ChouChun Huang, WenChin Wu Gaussian distribution is commonly used as a good approximation to study the trapped onecomponent Bosecondensed atoms with relatively small nonlinear effect. It is not adequate in dealing with the onecomponent system of large nonlinear effect, nor the twocomponent system where phase separation exists. We propose a modified Gaussian distribution which is more effective when dealing with the onecomponent system with relatively large nonlinear terms as well as the twocomponent system. The modified Gaussian is also used to study the breathing modes of the twocomponent system, which shows a drastic change in the mode dispersion at the occurrence of the phase separation. The results obtained are in agreement with other numerical results. [Preview Abstract] 
Thursday, March 8, 2007 4:54PM  5:06PM 
W32.00013: Study of impurities immersed in a trapped BoseEinstein condensate* Kwangsik Nho, D. P. Landau Using path integral Monte Carlo simulation methods[1], we have studied properties of impurities immersed in BoseEinstein Condensates harmonically trapped in low dimemsion. For twobody interactions, we use a hardsphere potential whose core radius equals its corresponding scattering length. We assume that the impurities experience the external trapping potential. We have tightly confined the motion of trapped particles in one or more direction by increasing the trap anisotropy in order to simulate lower dimensional atomic gases. By varying the strength of the bosonimpurity interactions and the number of impurities, we have investigated the effect of impurities on the energetics and structural properties such as the total energy, the density profile, and the superfluid fraction. Our results show that for impurities with larger twobody interactions than the bosonboson interactions, the impurities move away from the trap center and surround the trapped bosons, and the density profile is found to get narrower, with the peak density getting larger. The total superfluid fraction decreases due to the impurities, although the difference becomes smaller and smaller by increasing the trap anisotropy. \newline \newline \noindent *Research supported by NASA\\ \noindent [1] K.~Nho and D.~P.~Landau, Phys. Rev. A. {\bf 72}, 023615 (2005). [Preview Abstract] 
Thursday, March 8, 2007 5:06PM  5:18PM 
W32.00014: Modeling the Expansion of BoseEinstein Condensate Mixtures in the ThomasFermi Limit Alison Lota, Laura Halmo, Charles Holcombe, Mark Edwards We have studied the expansion of a mixture of $^{85}$Rb$^{87} $Rb BoseEinstein condensates within the ThomasFermi approximation. Systems involving mixtures of BoseEinstein condensates of different atomic species can be accurately modeled by coupled GrossPitaevskii equations. As for single condensates, the coupled GrossPitaevskii 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 (ThomasFermi approximation). In this case, it is possible to find timedependent ThomasFermi 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] 

W32.00015: ABSTRACT WITHDRAWN 
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