Bulletin of the American Physical Society
39th Annual Meeting of the APS Division of Atomic, Molecular, and Optical Physics
Volume 53, Number 7
Tuesday–Saturday, May 27–31, 2008; State College, Pennsylvania
Session P4: Bose-Einstein Condensates |
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Chair: Joseph Thywissen, University of Toronto Room: Nittany Lion Inn Ballroom AB |
Friday, May 30, 2008 11:00AM - 11:12AM |
P4.00001: Generation of effective magnetic fields in Raman-dressed states I.B. Spielman, Y.-J. Lin, W.D. Phillips, J.V. Porto We load a $^{87}$Rb BEC into the dressed states formed by a pair of far off resonant Raman beams. These counter-propagating beams are tuned to resonance between the three states in the linear-Zeeman split $F=1$ manifold. We show that we can adiabatically load a BEC into these spin and momentum superposition states and hold it for times $t>200$~ms. By changing the detuning between the Raman beams we transfer the BEC into states with non-zero momentum, which surprisingly are unmoving in the trapping potential. Finally we show that by applying a magnetic field gradient the atoms can move as do charged particles in a magnetic field. [Preview Abstract] |
Friday, May 30, 2008 11:12AM - 11:24AM |
P4.00002: Quantum quench in a spinor BEC Sabrina Leslie, Jennie Guzman, Mukund Vengalattore, Christopher Smallwood, Dan Stamper-Kurn We study the amplification of quantum fluctuations in a $^{87}$Rb spinor BEC that is rapidly quenched from its paramagnetic phase to its ferromagnetic phase, as a function of the quench end point. By characterizing the onset of spontaneous ferromagnetism and the amplification properties of the spinor condensate, we probe the initial quantum fluctuations from which the resulting structures evolve. To characterize the spinor condensate as an amplifier, we temporally and spatially resolve the evolution of the vector magnetization profile as a function of the quench end point. In particular, we describe the formation of transversely magnetized domains and vortices as a function of the end point. [Preview Abstract] |
Friday, May 30, 2008 11:24AM - 11:36AM |
P4.00003: Weakly interacting Bose-Einstein condensate in a disordered optical potential T.A. Corcovilos, D. Dries, J. Hitchcock, M. Junker, Y.P. Chen, R.G. Hulet We report on experimental progress in studying the behavior of a nearly noninteracting Bose-Einstein condensate (BEC) of $^7$Li atoms in a tunable disordered optical potential generated by laser speckle. We investigate the previously unexplored regime where the characteristic length scale of the disorder potential is shorter than the healing length, $\xi$, of the BEC. We increase $\xi$ by using a Feshbach resonance to tune the $s$-wave scattering length of the atoms to nearly zero (specifically, less than the Bohr radius). Under these conditions new phenomena, such as Anderson localization, are predicted. [Preview Abstract] |
Friday, May 30, 2008 11:36AM - 11:48AM |
P4.00004: Linewidth broadening in a $^{87}$Rb Bose-Einstein Condensate J.H.T. Burke, B. Deissler, K.J. Hughes, C.A. Sackett Bose-Einstein Condensates have been predicted to exhibit linewidth broadening [1,2]. We examine a condensate of $^{87} $Rb by probing the $5^{2}S_{1/2} F=2 \leftrightarrow 5^{2}P_ {3/2} F=3$ transition. Our magnetic trap has unusually weak confinement, which helps keep the resonant optical density from being too large to measure. Using this advantage, we measure the lineshape by scanning the probe in frequency across the resonance. We see approximatly a \%30 broadening of the linewidth with a polarization dependence that could be an effect of superradiance similar to what was observed by the group of Ketterle in [3]. Additionally, we measure the atom loss from the probe and observe an intensity dependent linewidth broadening which in the limit of low intensity tends towards the same broadening seen with absorption. We attribute the intensity dependence to multi-photon scattering. This intensity dependence was not observed when using photon absorption. \newline [1] J. Javanainen \textsl{Phys. Rev. Lett.} \textbf{72} 2375 (1994) \newline [2] L. You \textsl{et al. Phys. Rev. A} \textbf{53} 329 (1996) \newline [3] S. Inouye \textsl{et al. Science} \textbf{285} 571 (1999) [Preview Abstract] |
Friday, May 30, 2008 11:48AM - 12:00PM |
P4.00005: Bose-Einstein condensate inside a Bragg-reflecting atom cavity Rui Zhang, Rachel Sapiro, Natalya Morrow, Rahul Mhaskar, Georg Raithel We experimentally realize an atom cavity consisting of an optical lattice and a magnetic trap. On one side, atoms trapped in the cavity are confined by the magnetic potential, while on the other the atoms are Bragg-reflected by the optical lattice. We demonstrate this atom cavity by recording the momentum-space oscillation of a Bose-Einstein condensate (BEC) inside the cavity. The BEC is first created in the magnetic trap and then adiabatically loaded into the optical lattice. After a sudden displacement from the trap center, the BEC experiences a near-constant force and starts to accelerate. The following motion of the BEC is similar to a Bloch oscillation. The oscillation periods are measured and compared with theoretical predications. We further propose a Mach-Zehnder-type atom interferometer based on this atom-cavity configuration. [Preview Abstract] |
Friday, May 30, 2008 12:00PM - 12:12PM |
P4.00006: The a.c. and d.c. Josephson effects in a Bose-Einstein condensate Jeff Steinhauer, Shahar Levy, Elias Lahoud, Itay Shomroni We report the first observations of the a.c. and d.c. Josephson effects in a single BEC Josephson junction [1]. We also measure the chemical potential -- current relation of the BEC Josephson junction. The coherent tunneling of the BEC is qualitatively altered by the thermal cloud, whose presence is varied. The system reported here constitutes a trapped-atom interferometer with continuous readout, which operates on the basis of the a.c. Josephson effect. This BEC Josephson junction is the first application of our new type of BEC system with ultra high-resolution, capable of applying almost arbitrary potentials and imaging on a tunneling length scale. In the a.c. Josephson effect, a constant chemical potential difference (voltage) is applied, which causes an oscillating current to flow through the barrier. In the d.c. Josephson effect, a small constant current is applied, resulting in a constant supercurrent flowing through the barrier. In a sense, the particles do not ``feel'' the presence of the tall tunneling barrier, and flow freely through it with no driving potential. \newline \newline [1] S. Levy, E. Lahoud, I. Shomroni, and J. Steinhauer, \textit{Nature} \textbf{449}, 579-583 (2007). [Preview Abstract] |
Friday, May 30, 2008 12:12PM - 12:24PM |
P4.00007: Mean-field Stationary State of a Bose Gas at a Feshbach Resonance Andrew Carmichael, Juha Javanainen We study the steady state behaviour of a zero-temperature Bose gas close to a Feshbach resonance using a simple mean field model which allows for atomic and molecular condensates as well as correlated zero-momentum ``BCS'' pairs whose provenance would be dissociated zero momentum molecules. Beginning with a second quantized Hamiltonian and equations conserving total (free and bound) atom number and enforcing an assumption that atoms only appear either in the condensates or pairs and the usual Bogoliubov approximation, the system is numerically (and in certain limits, analytically) soluble in the steady state and exhibits a first order phase transition to a pure atomic condensate when the controllable parameters of the coupling and detuning are varied across an (analytically determined) transition line. Analysis of the thermodynamics of the zero-entropy system shows a negative pressure and hence mechanical instability on both sides of the resonance. A mathematical difficulty arising from an ultra-violet divergence due to the assumption of a zero range interaction is resolved with the help of a simpler, exactly analytically soluble two atom version of the problem. [Preview Abstract] |
Friday, May 30, 2008 12:24PM - 12:36PM |
P4.00008: The nonlinear enhancement of fractal structure in the escape dynamics of Bose condensates Kevin Mitchell, Boaz Ilan Theoretical predictions for the escape of ultracold and Bose-condensed atoms from a double-Gaussian optical trap have shown that novel self-similar fractal features could be visible within the escape data. These predictions were based on modeling the quantum evolution by ensembles of classical trajectories. This talk presents recent results on the full quantum simulation of this escape process. These simulations show the clear influence of quantum interference on the escape data. However, quantum effects do not destroy our ability to resolve the fractal behavior, verifying the robustness of the classical analysis. Furthermore, full numerical solutions of the Gross-Pitaevskii equation show that a negative scattering length (focusing nonlinearity) can enhance our ability to resolve fractal features in the classical phase space. [Preview Abstract] |
Friday, May 30, 2008 12:36PM - 12:48PM |
P4.00009: Bose Condensates with Small $s$-wave Scattering Lengths: Effect of Dipolar Interaction Yong Chen, D. Dries, J. Hitchcock, R.G. Hulet Using a variational approach, we have calculated the \textit {in}-\textit{situ} size and time-of-flight (TOF) expansion of a cylindrically symmetric Bose-Einstein Condensate (BEC) when the $s$-wave scattering length ($a_s$) is close to zero (which can be realized via, for example, a Feshbach resonance). We have specifically investigated the effect of dipolar interactions when the magnetic moment of the atoms is nonzero, and examined the dependence of the dipolar effect on the number of atoms, trap geometry and $a_s$. For a $^{52}$Cr BEC, we obtain quantitative agreement with observations in recent experiments [1], and predict a collapse due to dipolar interaction to occur at positive $a_s$ ($\sim$14$\pm$1$a_o$, using parameters similar to those in [1]). We have also performed calculations for BECs of alkali atoms, where the dipolar interactions are much weaker than in $^{52}$Cr. We will show how our calculations may help measure small $a_s$ and locate the zero- crossings. [1] T. Lahaye \textit{et al.}, Nature \textbf{448}, 672 (2007); J. Stuhler \textit{et al.}, Phys. Rev. Lett. \textbf{95}, 150406 (2005) [Preview Abstract] |
Friday, May 30, 2008 12:48PM - 1:00PM |
P4.00010: Bose-Einstein Condensation of Dark-State Polaritons Michael Fleischhauer, Johannes Otterbach, Razmik Unanyan We propose and theoretically analyse a mechanism for Bose-Einstein condensation of stationary dark-state polaritons (DSP) [1]. DSP's are quasi-particle arizing in the Raman interaction of light with three-level $\Lambda$-type systems. They are the basis of such phenomena as ultra-slow and stationary light. In contrast to exciton-polaritons, for which condensation has recently been observed [2], they have a long intrinsic lifetime, can be created with a three-dimensional quadratic dispersion profile, thus alleviating the need of resonators, and have a dynamically variable effective mass. Due to the very small effective mass the condensation temperature can be several orders of magnitude larger than that of atomic vapors. We introduce stationary dark-state polaritons, propose methods for their incoherent generation, and analyze their thermalization. Finally potential methods for an experimental verification of condensation will be discussed. \begin{description} \item{[1]} M. Fleischhauer and M.D. Lukin, PRL {\bf 84}, 5094 (2000); \\ F. Zimmer {\it et al.} arXiv:0712.0060 \item{[2]} J. Kasprzak {\it et al.} Nature {\bf 443}, 409 (2006) \end{description} [Preview Abstract] |
Friday, May 30, 2008 1:00PM - 1:12PM |
P4.00011: Slow Collisions of Bose-Einstein Condensates Bo Sun, Michael S. Pindzola, John A. Ludlow The dynamics of merging two initially independent Bose-Einstein condensates are studied by deforming a trap potential from a double well into a single well. The process is simulated by a full 3D calculation of the Gross-Pitaevskii equation. For cases in which both condensates begin in excited states, we find quite rich dynamics and complex final states. For example, when both condensates are in initial vortex states, or both are in initial soliton ring states, we find that additional vortices are created by the collision. We present probability density and current maps as a function of collision time in support of future experimental observations. [Preview Abstract] |
Friday, May 30, 2008 1:12PM - 1:24PM |
P4.00012: Cross-Molecular Coupling in Combined Photoassociation and Feshbach Resonances Matt Mackie, Jake Kesselman Photoassociation of a Feshbach-resonant condensate has revealed a shift of the laser resonance that is blue (red) below (above) the Feshbach resonance, as well as a rate constant that vanishes at a particular below-resonance magnetic field and saturates near-resonance at unprecedented values ($\sim10^{-7}$ cm$^3$/s). Here we report that cross-molecular coupling, enabled by the shared dissociation continuum, is implicated as the culprit behind these observations. [Preview Abstract] |
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