Bulletin of the American Physical Society
42nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 56, Number 5
Monday–Friday, June 13–17, 2011; Atlanta, Georgia
Session K3: Excitations in Bose and Spinor Gases |
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Chair: Mukund Vengalattore, Cornell University Room: A703 |
Wednesday, June 15, 2011 2:00PM - 2:12PM |
K3.00001: Long timescale dynamics in a degenerate F=1 $^{87}$Rb spinor Bose gas Jennie Guzman, Gyu-Boong Jo, Claire Thomas, Andre Wenz, Kater Murch, Dan Stamper-Kurn We report on the long timescale behavior of a quasi two-dimensional spinor gas produced by cooling unmagnetized F=1 $^{87}$Rb spin mixtures. Using in-situ magnetization sensitive imaging, we are able to spatially and temporally resolve the vector magnetization profile of the spinor condensate. We explore the long timescale properties of the ferromagnetic (paramagnetic) spinor condensate at variable quadratic shift. At short evolution times, transverse and longitudinal ferromagnetic domains and domain walls spontaneously form throughout the condensate, while at long evolution times we observe the system evolve towards a homogeneously magnetized condensate, independent of the initially prepared spin mixture. [Preview Abstract] |
Wednesday, June 15, 2011 2:12PM - 2:24PM |
K3.00002: Role of topological defects in the dynamics of quenched spinor gases Srivatsan Chakram, Lauren Aycock, Mukund Vengalattore Recent experiments on $^{87}$Rb spinor condensates quenched from the polar to the ferromagnetic state have observed the spontaneous formation of spin textures and topological defects identified as polar core spin vortices [1]. Spin correlations seen in experimental and theoretical studies [2] of the quench disagree with those expected for a thermalized final state. This absence of thermalization might be due to spin vortices which are seen to persist over experimental time scales. As has been shown[3], the dynamics of these ``coreless'' vortices are distinct from that exhibited by ``charge'' vortices in a scalar superfluid [4]. Elucidating the dynamics of these spin vortices is key to understanding the non-equilibrium physics of quenched spinor gases. We investigate the dynamics of topological defects such as polar core vortices, merons and domain walls that could be generated during the quantum quench. We conclude with proposed experimental schemes for the deterministic generation and study of these defects.\\[0pt] [1] L. E. Sadler, J. M. Higbie, S. R. Leslie, M. Vengalattore and D. M. Stamper-Kurn, Nature 443, 312 (2006); [2] R.Barnett, M. Vengalattore and A. Polkovnikov, arXiv:1009.1646v2 (2010); [3] Ari M. Turner, Phys. Rev. Lett. 103, 080603 (2009); [4] C. Weiler, T. Neely, D. Scherer, A. Bradley, M. Davis, and B. Anderson, Nature 455, p.948 (2008) [Preview Abstract] |
Wednesday, June 15, 2011 2:24PM - 2:36PM |
K3.00003: Algebraic Origins of Reflectionless Scattering in Bogoliubov-de Gennes equations for a solitonic BEC Andrew Koller, Maxim Olshanii We consider small excitations around a one-dimensional bosonic soliton. It is well known that the corresponding Bogoliubov-de Gennes (BdG) Liouvillian features a vanishing reflection coefficient at all energies.\footnote{D. J. Kaup, J. Phys. A {\bf 42}, 5689 (1990).}$^,$\footnote{Y. Castin, Eur. Phys. J. B {\bf 68}, 317 (2009).} In this presentation, we show that this reflectionless property can be explained via an algebraic link (related to quantum-mechanical supersymmetry) to a potential-free Liouvillian. [Preview Abstract] |
Wednesday, June 15, 2011 2:36PM - 2:48PM |
K3.00004: Probing Bogoliubov phonons in quasi-2D BECs Lin Xia, Dan Lobser, Eric Cornell Quasi-2D condensate slices are created by loading a 3D Bose-Einstein condensate into a 1D optical lattice. Using a microwave pumping scheme a single layer is isolated. Bogoliubov phonons are projected onto free particles by rapidly turning off interatomic interactions. A temporal focusing technique is used to probe the momentum distribution of the resulting cloud. We measure correlations between density fluctuations at k and -k in the images and compare with Bogoliubov theory. This work funded by ONR and NSF. [Preview Abstract] |
Wednesday, June 15, 2011 2:48PM - 3:00PM |
K3.00005: ABSTRACT WITHDRAWN |
Wednesday, June 15, 2011 3:00PM - 3:12PM |
K3.00006: Generation and pinning of high winding-number vortices in Bose-Einstein condensates E. Carlo Samson, Kali Wilson, Zachary Newman, Ewan Wright, Brian P. Anderson We demonstrate the generation of pinned vortices with high winding numbers (up to 11) in Bose-Einstein condensates (BECs) held in highly oblate traps. In our method, a pancake-shaped BEC is initially produced in a combined magnetic and optical trap. Using time-varying magnetic fields to translate the position of the BEC with respect to a focused blue-detuned laser beam, we allow the BEC to spiral around the optical barrier until the barrier ends up at the BEC center. We explore the variation of the net winding number of the pinned vortices with the duration of the spiral trajectory. This procedure may be scaled to larger numbers of pinned vortices and will be useful in studies of superfluid dynamics and vortex interactions. [Preview Abstract] |
Wednesday, June 15, 2011 3:12PM - 3:24PM |
K3.00007: Dynamical excitations in a toroidal Bose-Einstein condensate Kevin C. Wright, A. Ramanathan, R.B. Blakestad, W.D. Phillips, G.K. Campbell Superfluids flow without dissipation if the flow velocity is below a threshold determined by the lowest energy excitation of the system. We have created a smooth, continuous BEC in a multiply-connected (toroidal) geometry, and investigated the dynamical characteristics of the system by inducing long-lived persistent currents, and perturbing these currents with localized repulsive optical barriers. Dynamical instability caused by the barriers can create quasiparticle excitations in the BEC (e.g. phonons, solitons, vortices) depending on the nature of the perturbation and the system geometry. If the perturbation is large enough, these excitations cause discrete phase slips which change the circulation state of the BEC around the ring. We have examined some of these dynamical processes in our toroidal BEC over a range of experimental conditions. [Preview Abstract] |
Wednesday, June 15, 2011 3:24PM - 3:36PM |
K3.00008: Example of a Quantum Anomaly in the Physics of Ultracold Gases Maxim Olshanii, H\'{e}l\`{e}ne Perrin, Vincent Lorent We propose an experimental scheme for the observation of a quantum anomaly---quantum-mechanical symmetry breaking--in a two-dimensional harmonically trapped Bose gas.\footnote{Maxim Olshanii, H\'{e}l\`{e}ne Perrin, Vincent Lorent, Phys.\ Rev.\ Lett. 105, 095302 (2010).} The anomaly manifests itself in a shift of the monopole excitation frequency away from the value dictated by the Pitaevskii-Rosch dynamical symmetry.\footnote{L. P. Pitaevskii and A. Rosch, Phys.\ Rev.\ A 55, R853 (1997).} While the corresponding classical Gross-Pitaevskii equation and the hydrodynamic equations derived from it do exhibit this symmetry, it is---as we show in our paper---violated under quantization. The resulting frequency shift is of the order of 1\% of the carrier, well in reach for modern experimental techniques. We propose using the dipole oscillations as a frequency gauge. [Preview Abstract] |
Wednesday, June 15, 2011 3:36PM - 3:48PM |
K3.00009: Quasi-1D Bose gas experiments: a quantitative study via the stochastic Gross-Pitaevskii equation Stuart P. Cockburn, Donatello Gallucci, Nick P. Proukakis A number of quantitative experiments have been performed in the last few years looking at properties of very elongated weakly-interacting quasi-one-dimensional Bose gases, where fluctuations have to be taken fully into account. We show here that a treatment based on a modified stochastic Gross-Pitaevskii equation provides an accurate ab initio model for describing such experiments. In particular, our approach reproduces accurately the in situ density profiles obtained in the experiments of Trebbia et al. [Phys. Rev. Lett. 97, 250403 (2006)] and van Amerongen et al. [Phys. Rev. Lett. 100, 090402 (2008)], while excellent agreement is found between the SGPE density fluctuation data and that from the recent experiment of Armijo et al. [Phys. Rev. Lett. 105, 230402 (2010)]. Our treatment is based on explicitly solving a one-dimensional stochastic Gross-Pitaevskii equation, with the effect of beyond-ground-state transverse occupied modes accounted for by simultaneously modifying the inherent system nonlinearity and treating thermally excited transverse modes as independent, ideal Bose gases. [Preview Abstract] |
Wednesday, June 15, 2011 3:48PM - 4:00PM |
K3.00010: Nonlinear matter-wave amplification in a $^{23}$Na spinor Bose-Einstein condensate Jonathan Wrubel, Paul Griffin, Hyewon Pechkis, Jianing Han, Ryan Barnett, Eite Tiesinga, Paul Lett An $F=1$, $^{23}$Na Bose-Einstein condensate (BEC) in a far off-resonant optical trap has a spinor order parameter for the hyperfine sublevels $m_F=+1,0,-1$. At low magnetic fields pairs of atoms may undergo spin-changing collisions between the $|m_{F_A},m_{F_B}>=|0,0>$ and $|+1,-1>$ states. The ground state is a BEC in the $m_F=0$ state. However, by dressing the $F=1$ energy levels with a microwave field off-resonant from the $F=2$ state, the sign of the effective quadratic Zeeman energy is reversed and the $m_F=0$ BEC becomes metastable. Vacuum fluctuations in the initially empty $m_F=+1,-1$ states drive nonlinear amplification of $|+1,-1>$ atom pairs. When the energy difference is equal to an interaction energy, then the rate of emission of $|+1,-1>$ pairs is maximal. This realizes a phase-insensitive parametric amplifier for matter waves and is characterized by sub-shot-noise spin correlations between the $m_F=+1$ and $m_F=-1$ BECs. We discuss progress in realizing this amplifier in a Na BEC as well as possibilities for building a nonlinear matter-wave interferometer. [Preview Abstract] |
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