Bulletin of the American Physical Society
2005 36th Meeting of the Division of Atomic, Molecular and Optical Physics
Tuesday–Saturday, May 17–21, 2005; Lincoln, Nebraska
Session C4: Bose Einstein Condensation I |
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Chair: Gil Summy, Oklahoma State University Room: Burnham Yates Conference Center Hawthorne |
Wednesday, May 18, 2005 1:30PM - 1:42PM |
C4.00001: Time-Dependent Wavepacket Propagation using the Lie-Trotter-Suzuki Method Barry I. Schneider, Lee A. Collins The Lie-Trotter-Suzuki(LTS) formulae offer an extremely efficient approach to the solution of the time-dependent Schroedinger equation. By combining finite difference or finite element discrete variable spatial discretizations with the LTS formula, we have developed a computational method, accurate up to fourth order, and have applied it to a number of interesting problems. The algorithm is explicit, unconditionally stable, scales linearly with the number of basis functions used for the spatial discretization and is easily parallelized. A number of the applications, including a model for a BEC interferometer, will be presented in the talk. [Preview Abstract] |
Wednesday, May 18, 2005 1:42PM - 1:54PM |
C4.00002: Photon Recoil Momentum in Dispersive Media Gretchen K. Campbell, Aaron E. Leanhardt, Jonchul Mun, Micah Boyd, Erik Streed, Wolfgang Ketterle, David E. Pritchard We have measured a systematic shift of the photon recoil momentum due to the index of refraction of a dilute gas of atoms. The recoil frequency was measured with a two pulse light grating interferometer using near resonant laser light. By measuring the resulting frequency as a function of the laser detuning, we found a distinctive dispersive shape for $\omega_{rec}$ that fit the recoil momentum as $n\hbar k$, where $n$ is the index of refraction of the gas. For high atomic densities, this shift can have a significant effect on atom interferometers, and is of particular importance for precision measurements of $h/m$ with cold atoms. [Preview Abstract] |
Wednesday, May 18, 2005 1:54PM - 2:06PM |
C4.00003: Direct, non-destructive imaging of transverse and longitudinal magnetization in a bose gas: II Shin Inouye, James Higbie, Lorraine Sadler, Ananth Chikkatur, Sabrina Leslie, Kevin Moore, Veronique Savalli, Dan Stamper-Kurn The behavior of transverse and longitudinal magnetization of an ultracold thermal cloud was studied using polarization sensitive phase-contrast imaging. The decay time of the transverse magnetization signal was 65ms. This was more than factor of 10 shorter than the one equivalent decay time for the BEC, and was sensitive to magnetic field gradient across the cloud. This result can be understood with a simple kinetic model. [Preview Abstract] |
Wednesday, May 18, 2005 2:06PM - 2:18PM |
C4.00004: Multi-state fermionic Hamiltonian approach to the study of the BEC-BCS crossover in ultracold fermionic atom gases. B. Mihaila, M.M. Parish, S. Gaudio, E. Timmermans, K.B. Blagoev, A.V. Balatsky, D.L. Smith, P.B. Littlewood We study the crossover between the BEC and BCS regimes in an ultracold fermionic atom gas, in the framework of a multi-state fermionic Hamiltonian using a finite-range interaction. We compare the predictions for the ground-state properties of a 2- state (one-channel) model, with the ground-state properties of a 3-state ($^{40}$K-like), and a 4-state ($^{6}$Li-like) model, respectively. We discuss signatures of the onset of superfluidity as predicted by the $s$-wave mean-field approximation of the zero-temperature Hamiltonian. [Preview Abstract] |
Wednesday, May 18, 2005 2:18PM - 2:30PM |
C4.00005: Bogoliubov excitations of two-component BEC supported by different vortex configurations Sungjong Woo, Stephen Choi, Leslie Baksmaty, Nicholas Bigelow We have studied the Bogoliubov excitations of a rotating two-component trapped BEC with a vortex lattice or vortex sheets using the mean-field formalism. It is known that different ground state configurations of vortex lattices are possible depending on the relative magnitudes of the interaction strengths between particles. We have observed the Tkachenko modes and the hydrodynamic bulk excitations for each vortex configuration, a triangular or rectangular lattice or vortex sheets, and analyze the similarities and differences with a single component case. We also discuss about the dramatic enhancement of the resonance effect of certain surface modes with the vortex dynamics that had been observed before for the single component BEC. [Preview Abstract] |
Wednesday, May 18, 2005 2:30PM - 2:42PM |
C4.00006: Experiments with an ultracold mixture of $^{85}$Rb and $^{87}$Rb Scott B. Papp, Juan M. Pino II, Carl E. Wieman Magnetic field tunable Feshbach resonances are an invaluable tool for manipulating the inter-particle interactions in a Bose Einstein condensate (BEC). The $^{85}$Rb Feshbach resonance in collisions between two atoms in the low field seeking \textit{F} = 2, \textit{m$_F$} = $-2$ state is particularly convenient since it occurs at a moderate magnetic field of 155 G and spans more than 10 G. However, $^{85}$Rb is difficult to evaporatively cool due to large inelastic loss rates and a zero in the elastic cross section near 400 ${\mu}$K. We have designed and constructed an apparatus to overcome these challenges by making use of the favorable elastic cross section between $^{85}$Rb and $^{87}$Rb. We can obtain large $^{87}$Rb condensates in either the \textit{F} = 2, \textit{m$_F$} = 2 or the \textit{F} = 1, \textit{m$_F$} = $-1$ state. The $^{85}$Rb gas is sympathetically cooled due to thermal contact with the $^{87}$Rb gas. We discuss our results on cooling $^{85}$Rb to quantum degeneracy. With this system we also have the opportunity to study interspecies interactions. A Feshbach resonance is predicted to exist between $^{87}$Rb and $^{85}$Rb in magnetically trappable states at 270 G. We will discuss our observation of this interspecies Feshbach resonance. We acknowledge funding for this work from the NSF and ONR. One of us (S. B. P.) acknowledges the support of an NSF Graduate Research Fellowship. [Preview Abstract] |
Wednesday, May 18, 2005 2:42PM - 2:54PM |
C4.00007: Time averaged optical dipole traps for cold atoms Peyman Ahmadi, Brian Timmons, Gil Summy Achieving high atom populations in optical traps, (created by laser light far-detuned to the red of an atomic resonance, FORT) is essential for various experiments especially for all optical realization of a Bose-Einstein condensate. However an efficient loading of these traps still remains a challenge. The focus of this talk is to explain a new approach of maximizing optical trap populations. We show that the FORT population (N$_{FORT})$, which is proportional to the FORT volume, saturates once a certain potential depth is reached. Our goal is to increase the volume and keep the potential depth at its saturation limit. This is accomplished by a fast sweeping of the FORT beams while loading takes place. We observe a considerable increase in N$_{FORT }$for certain amplitudes and frequencies of the sweeping. A detailed study of these time averaged optical traps will be presented. [Preview Abstract] |
Wednesday, May 18, 2005 2:54PM - 3:06PM |
C4.00008: Collisions in a gas of metastable helium near quantum degeneracy Signe Seidelin, Jose Gomes, Rodolphe Hoppeler, Olivier Sirjean, Denis Boiron, Chris Westbrook, Alain Aspect Experiments with an atomic cloud of metastable helium (He*) in the vicinity of Bose-Einstein condensation will be presented. The metastability of the atoms has opened the door for using new and original detection methods: due to their internal energy, the atoms can be detected electronically by means of a micro-channel plate. The use of He* is also interesting due to the presence of ionizing collisions in the sample. The He$^{+}$ ions produced in collisions between the metastable atoms can be detected in real- time, and the ion signal constitutes an alternative and useful diagnostic. In particular, this signal allows one to identify very precisely the Bose-Einstein condensation threshold. One of the advantages of using this signal to probe the cloud is its ``non-invasive'' nature: observing the ions does not at all alter the natural evolution of the cloud, in contrast to the ordinary detection technique which consists of releasing the atoms from the trap and then imaging the cloud. In the experiments to be discussed, by using this new diagnostics based on the ion signal, we have measured some important parameters governing both elastic and inelastic collisions: the ionizing rate constants and the scattering length for metastable helium. [Preview Abstract] |
Wednesday, May 18, 2005 3:06PM - 3:18PM |
C4.00009: The phase transition in ground state configurations of a vortex lattice in an AMBEC Sungjong Woo, Nicholas Bigelow, Q-Han Park We study the ground state vortex configurations in a trapped atomic-molecular Bose-Einstein condensate with nontrivial angular momentum imposed in the system. We have confirmed a zero-temparature phase transition in the ground state vortex configurations between a rectangular lattice and a triangular paired vortex configuration, with rotational speed of the condensate as a parameter, analytically and numerically. A new type of dynamics involving the paired vortex lattice is also discussed. [Preview Abstract] |
Wednesday, May 18, 2005 3:18PM - 3:30PM |
C4.00010: Correlation properties of atoms in two strongly coupled waveguides Vanja Dunjko, Maxim Olshanii Behavior of an atomic gas in two neighboring waveguides is governed by a coupled two-specie Lieb-Liniger model. When tunnelling between two Lieb-Liniger gases is greater than all other energy scales, it is possible to treat the coupled system as a new Lieb-Liniger gas with an effective coupling constant, which we compute. The elements of the two-body density matrix involving excited dressed states are slaved to the density matrix of the effective Lieb-Liniger gas. Using these functions, we compute the relative phase fluctuations between the coupled gases, and compare with Whitlock and Bouchoule's results [Phys. Rev. A \textbf{68}, 053609 (2003)] valid for arbitrary tunnelling but weak interatomic interaction. [Preview Abstract] |
Wednesday, May 18, 2005 3:30PM - 3:42PM |
C4.00011: Coherent Molecular Optics using Sodium Dimers Daniel Miller, Kaiwen Xu, Jamil Abo-Shaeer, Jitkee Chin, Yingmei Liu, Wolfgang Ketterle Coherent molecular optics is performed using two-photon Bragg scattering. Molecules were produced by sweeping an atomic Bose-Einstein condensate through a Feshbach resonance. The spectral width of the molecular Bragg resonance corresponded to an instantaneous temperature of 20 nK, indicating that atomic coherence was transferred directly to the molecules. An autocorrelating interference technique was used to observe the quadratic spatial dependence of the phase of an expanding molecular cloud. Finally, atoms initially prepared in two momentum states were observed to cross-pair with one another, forming molecules in a third momentum state. This process is analogous to sum-frequency generation in optics. [Preview Abstract] |
Wednesday, May 18, 2005 3:42PM - 3:54PM |
C4.00012: Dynamical instability induced domain formation in a spin-1 condensate Wenxian Zhang, Duanlu Zhou, L. You Dynamical instability induced domain formation is an important topic in condensate physics, and has been carefully studied recently for a two component Bose-Einstein condensate (BEC) with conserved numbers of atoms for each component\footnote{K. Kasamatsu and M. Tsubota, Phys. Rev. Lett. {\bf 93}, 100402 (2004).}. In this study, we consider the same problem for a spin-1 condensate, where the numbers of atoms for each spin component can change due to the asymmetric spin mixing interaction, or spin exchange collisions of the type $2|F=1,m_F=0\rangle\leftrightarrow |F=1,m_F=-1 \rangle+ |F=1,m_F=1\rangle$. Our theoretical studies can be confirmed by a detailed observation of the off-equilibrium condensate dynamics from a sudden change of an external magnetic field. [Preview Abstract] |
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C4.00013: Bose-Einstein condensation of dipolar atoms Juergen Stuhler, Axel Griesmaier, Marco Fattori, Tobias Koch, Sven Hensler, Joerg Werner, Tilman Pfau We report on the realization of a Bose-Einstein condensate (BEC) of chromium with up to 50,000 condensed $^{52}$Cr atoms. The large magnetic dipole moment (6 Bohr magnetons) of chromium is unique among all species that have been Bose condensed so far. The preparation of the $^{52}$Cr BEC requires novel cooling strategies that are adapted to its special electronic properties and to its dipolar character. The final step to reach quantum degeneracy is forced evaporative cooling of $^{52}$Cr atoms within a crossed optical dipole trap. At a critical temperature of Tc $\sim $ 700 nK, we observe Bose-Einstein condensation of chromium by the appearance of a two-component velocity distribution. Released from an anisotropic trap, the BEC expands with an inversion of the aspect ratio. Exploiting one of our recently observed Feshbach resonances to tune the isotropic contact interaction should allow us to realize a dipolar BEC in which the magnetic dipole-dipole interaction is dominant. This will widely open the door for experimental studies of the effects of long-range and anisotropic dipolar interactions in degenerate quantum gases. Since chromium is the standard material in atom lithography, a $^{52}$Cr BEC has potential for use in technical applications as a coherent source of atoms in nanostructuring processes. [Preview Abstract] |
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