### Session J6: Bose-Einstein Condensation

Chair: Hal Metcalf, Stony Brook University
Room: Arboretum IV-V

 Thursday, May 27, 2010 8:00AM - 8:12AM J6.00001: Transfer and Storage of Optical Information in a Spinor Bose-Einstein Condensate L. Suzanne Leslie , Azure Hansen , Nicholas Bigelow Our previous experimental work has focused on the coherent transfer of optical information to a 87Rb Bose-Einstein condensate (BEC). We accomplish this through the use of a two-photon, stimulated-Raman technique that encodes the difference in angular momentum (both spin and orbital) of two Raman beams into the amplitude and phase of the spinor order parameter of the condensate. In particular, the orbital angular momentum of a Laguerre-Gaussian beam can be coherently transferred to the BEC and stored as a coreless vortex. The long coherence times of BECs and the topological stability of coreless vortices make them interesting candidates for information storage and manipulation. This information can be read back out of the condensate into light by reapplying one of the two Raman beams which then stimulates emission into the other Raman mode. The emitted light can be used to confirm both the transfer and storage of information in the BEC. Thursday, May 27, 2010 8:12AM - 8:24AM J6.00002: BEC manipulation with fictitious magnetic fields Jeffrey Heward , Mark Edwards , Charles W. Clark The interaction of Bose-Einstein condensate (BEC) atoms with counterpropagating laser beams can often be represented by fictitious magnetic fields [1]. These fictitious fields can be combined with ordinary magnetic fields to produce total fields whose amplitudes vary in space on the scale of the laser wavelength. When the strengths of such magnetic fields are positioned in the neighborhood of a Feshbach resonance, it can produce a spatial variation of the binary scattering length of the condensate atoms. We have studied how these fields can be used to engineer the shape and behavior of BEC's for typical experimental arrangements. We present results for $^{87}$Rb condensate shapes for BEC that can be formed when condensates are formed in the presence of spatially varying scattering lengths as well as the effects of turning on and off the fictitious magnetic fields in the presence of expanding condensates. All of the behaviors presented represent solutions of the time--independent and time--dependent Gross--Pitaevskii (GP) equation. Finally we comment briefly on cases where the GP equation breaks down.\\[4pt] [1] I. Deutsch and P. Jessen, {\bf 57}, 1972 (1998). Thursday, May 27, 2010 8:24AM - 8:36AM J6.00003: Probing quasi-2D condensates using $\it{in situ}$ and focusing imaging methods Shihkuang Tung , Giacomo Lamporesi , Daniel Lobser , Lin Xia , Eric Cornell A 2D interacting Bose gas in an infinite uniform system doesn't undergo Bose-Einstein condensation due to long-wavelength thermal fluctuations. Instead, a Berezinskii- Kosterlitz-Thouless (BKT) transition is predicted. The system goes from superfluid state to normal state by dissociating vortex and anti-vortex pairs when approaching the transition temperature from below. However, in a finite inhomogeneous quasi-2D system, the process of the transition coming from normal state to BEC state is still not clear. We report our latest results on probing quasi-2D condensates using two different imaging techniques, $\it{in situ}$ and focusing imaging. The $\it{in situ}$ imaging and the focusing imaging methods probe the quasi-2D gas in coordinate space and in momentum space respectively. The two distributions provide different crucial information about the properties of an interacting quasi-2D Bose gas in an inhomogeneous trapped system. Thursday, May 27, 2010 8:36AM - 8:48AM J6.00004: Observing Vortex Dynamics in a Bose-Einstein Condensate David Hall , Daniel Freilich , Dylan Bianchi , Adam Kaufman , Thomas Langin Nondestructive imaging techniques make possible the observation of condensate dynamics in the examination of a single atomic sample. This ability is especially useful when initial experimental conditions are difficult or impossible to reproduce, or when random processes play an important role. Established nondestructive techniques are of limited use, however, for observing excitations such as quantized vortices, for which the characteristic length scale is much smaller than the wavelength of the probe light. We describe here our successful experimental implementation of a quasi-nondestructive imaging method that opens a dramatic new window into the dynamics of one, two, and many-vortex condensate configurations. Thursday, May 27, 2010 8:48AM - 9:00AM J6.00005: Persistent flow in a toroidal BEC with a tunable barrier Kevin Wright , Sergio Muniz , Anand Ramanathan , William Phillips , Gretchen Campbell We are investigating the stability of persistent flow in a toroidal BEC. The BEC is held in a red-detuned optical trap formed by two beams: a tightly focused sheet'' of light providing tight vertical confinement, and a Laguerre-Gaussian beam confining the BEC to a ring in the radial direction. To this trap we have added a blue-detuned light sheet to create a variable weak link'' in the ring. The geometry of this BEC system is analogous to that of a superconducting quantum interference device (SQUID). We will present results of our investigation of this system, and discuss prospects for realizing an atomic analog of a SQUID. Thursday, May 27, 2010 9:00AM - 9:12AM J6.00006: Bose-Einstein condensation of $^{84}$Sr Y. Natali Martinez de Escobar , B.J. DeSalvo , P.G. Mickelson , M. Yan , T.C. Killian We observe Bose-Einstein condensation (BEC) in the alkaline-earth metal atom strontium (Sr). Bosonic $^{84}$Sr possesses ideal collisional properties for efficient evaporative cooling to quantum degeneracy despite not being the isotope of choice due to its unfavorably low natural abundance (0.6{\%}). This newly condensed element offers novel experimental possibilities, such as using an optical Feshbach resonance to tune atom-atom interactions with relatively low atomic losses. Equally exciting theoretical proposals use quantum fluids made of alkaline-earth atoms to create exotic quantum magnetism states and demonstrate quantum computation in optical lattices. Thursday, May 27, 2010 9:12AM - 9:24AM J6.00007: Bose-Einstein condensation of strontium Meng Khoon Tey , Simon Stellmer , Bo Huang , Rudolf Grimm , Florian Schreck We report on the attainment of Bose-Einstein condensation with ultracold strontium atoms. We use the $^{84}$Sr isotope, which has a low natural abundance but offers excellent scattering properties for evaporative cooling. By accumulating the atoms in a metastable state during the initial MOT phase, followed by narrowline cooling, and straightforward evaporative cooling in an optical trap, we obtain pure condensates containing $1.5\times10^5$ atoms. This puts $^{84}$Sr in a prime position for experiments on quantum-degenerate gases involving atomic two-electron systems. Furthermore, we report on recent advances towards a degenerate Fermi gas of $^{87}$Sr. Thursday, May 27, 2010 9:24AM - 9:36AM J6.00008: Quantum hydrodynamics of binary BECs Peter Engels , JiaJia Chang , Chris Hamner We investigate the quantum hydrodynamics of a binary BEC. We introduce relative motion between the two components of a binary BEC and experimentally observe intriguing nonlinear dynamics including the formation of dark/bright solitons and inter-component quantum shocks. This talk will present our recent results and the current status of the experiment. Thursday, May 27, 2010 9:36AM - 9:48AM J6.00009: Nonlinear structures in one and two-mode BECs Douglas Faust , William P. Reinhardt In recent years, precise control of optical potentials has allowed coherent BECs to be split into multiple entities. The most famous example is the superfluid to Mott insulator transition, where phase coherence is completely lost between wells. Alternatively, a specific phase relationship characterizes other structures - such as solitons and Josephson junctions - in quantum gasses. We present results from a novel computational method which is able to break the spatial symmetry of a mean-field state which evolves into multiple entities and gives a full accounting of both non-linear effects and tunneling to access the superfluid and Mott insulator regimes as well as give, previously unknown, details of the transition between them. Our results include characterizing BEC atom interferometry experiments and an investigation of two-mode analogues of one-mode structures such as solitons and phase-driven oscillations. Thursday, May 27, 2010 9:48AM - 10:00AM J6.00010: Atomic Four-Wave Mixing with Two-Component Matter Waves Daniel Pertot , Bryce Gadway , Dominik Schneble We report on a novel type of atomic four-wave mixing occurring in a two-component Bose--Einstein condensate. Seed and pump modes differing both in momentum and internal state are prepared via state-selective Kapitza--Dirac diffraction from a one-dimensional optical lattice. We find the initially empty output modes to be populated through a collinear four-wave mixing process involving both internal states, in excellent agreement with simulations based on a coupled-mode expansion of the Gross--Pitaevskii equation. We show how such four-wave mixing can affect studies of bosonic mixtures loaded into optical lattices, and we discuss possible applications in the context of quantum atom optics.