Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session L16: Cold Gases: Spin, Rotation, and Reduced Dimension |
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Sponsoring Units: DAMOP Chair: Ludwig Mathey, National Institute of Standards and Technology Room: 317 |
Tuesday, March 17, 2009 2:30PM - 2:42PM |
L16.00001: Spin Structure and Critical Nucleation Frequency of Fractionalized Vortices in 2D Topologically Ordered Superfluids of Cold Atoms Junliang Song, Fei Zhou We have studied spin structures of fluctuation-driven fractionalized vortices and topological spin order in 2D nematic superfluids of cold sodium atoms. Our Monte Carlo simulations suggest a softened $\pi$-spin disclination structure in a half-quantum vortex when spin correlations are short ranged; in addition, calculations indicate that a unique non-local topological spin order emerges simultaneously as cold atoms become a superfluid below a critical temperature. We have also estimated fluctuation-dependent critical frequencies for half-quantum vortex nucleation in rotating optical traps and discussed probing these excitations in experiments. [Preview Abstract] |
Tuesday, March 17, 2009 2:42PM - 2:54PM |
L16.00002: Vortex lattice locking in rotating two-component Bose-Einstein Condensates Ryan Barnett, Edward Chen, Mason Porter, Hans Peter Buchler, Gil Refael The vortex density of a rotating superfluid, divided by its particle mass, dictates a superfluid's angular velocity through the Feynman relation. To find how the Feynman relation applies to superfluid mixtures, we investigate a rotating two- component Bose Einstein condensate, composed of bosons with different masses. We find that in the case of sufficiently strong interspecies attraction, the vortex lattices of the two condensates lock and rotate at the drive frequency, while the superfluids themselves rotate at two different velocities, whose ratio is that of the particle masses of the two species. In this talk, I will characterize the vortex-locked state, establish its regime of stability, and find that it survives within a disk smaller than a critical radius, beyond which vortices become unbound. Finally, numerical solution of the coupled Gross-Pitaevskii equations in support of this will be presented. [Preview Abstract] |
Tuesday, March 17, 2009 2:54PM - 3:06PM |
L16.00003: Quantum fluctuations of a Bose-Josephson junction on a quasi-one-dimensional ring trap Nicolas Didier, Anna Minguzzi, Roberta Citro, Frank W.J. Hekking Ring traps for ultracold atomic gases are becoming experimentally feasible. We study the theory of quantum fluctuations of a Bose Einstein condensate confined to a quasi one-dimensional ring trap where a Josephson junction is realized with a localized barrier potential. We consider the situation where the transverse confinement of the trap is so tight that only longitudinal quasi-1D motion is allowed along the ring. The condensate is treated as a Luttinger liquid and the low energy properties are described within the bosonization formalism. For a very large barrier, we study the one-particle density-matrix including the correction due to the density fluctuations. Our analysis reveals different power law decays depending on the location of the probed points, i.e. whether they are chosen in the bulk or at the edge of the ring under consideration. This quasi-long range order could be probed using an interference measurement. In the Tonks-Girardeau limit, the density-density correlation function tends to the exact result obtained from the Bose-Fermi mapping. The momentum distribution is calculated and compared to the result for a very small barrier. Furthermore, for a barrier of finite height, within the renormalization group approach, we study how quantum fluctuations reduce the effective Josephson coupling energy. [Preview Abstract] |
Tuesday, March 17, 2009 3:06PM - 3:18PM |
L16.00004: Detecting statistics of quasiparticles using dynamical probes Claudia De Grandi, Roman Barankov, Anatoli Polkovnikov We study a time-dependent sine-Gordon model in the range of the coupling costant (Luttinger parameter) where the quasiparticles excitations change from massive bosons to free fermions. We find that, if we include the effects of finite temperature, the non-adiabatic response to slow perturbations is enhanced for the bosonic case and reduced for the fermionic one with respect to zero temperature. The signature of this \textit{bunching (anti-bunching)} behaviour can also be seen at zero temperature by analyzing the second order corrections of a perturbative approach in the number of quasiparticles created. This suggests the existence of a crossover (for the Luttinger parameter) that separates systems with bose-like statistics from systems with fermi-like statistics, and therefore time-dependent perturbations to the system can be used to probe the statistics of the quasiparticles. We show how this model is relevant for cold atoms experiments that realize splitting and merging of two one-dimensional bose gases. [Preview Abstract] |
Tuesday, March 17, 2009 3:18PM - 3:30PM |
L16.00005: Motion of an impurity in a one-dimensional quantum liquid Austen Lamacraft We consider the motion of an impurity particle in a general one-dimensional quantum fluid at zero temperature. The dispersion relation $\Omega(P)$ of the impurity is strongly affected by interactions with the fluid as the momentum approaches $\pm\pi\hbar n, \pm 3\pi\hbar n, \ldots$, where $n$ is the density. This behavior is caused by singular $\pm 2\pi\hbar n$ scattering processes and can be understood by analogy to the Kondo effect, both at strong and weak coupling, with the possibility of a quantum phase transition where $\Omega'(\pm \pi n)$ jumps to zero with increasing coupling. The low energy singularities in the impurity spectral function can be understood on the same footing. [Preview Abstract] |
Tuesday, March 17, 2009 3:30PM - 3:42PM |
L16.00006: Breakdown of Macroscopic Quantum Self Trapping in Coupled 1D Bose Gases Rafael Hipolito, Roman Barankov, Anatoli Polkovnikov Two coupled 3D Bose-Einstein condensates with a large population imbalance exhibit macroscopic quantum self-trapping if the ratio of interaction energy to the coupling energy between the two gases is above a critical value. Above the self trapping transition, one sees only small amplitude high frequency oscillations of the population difference. In the analogous case of 1D coupled gases we find similar behavior for short times, but quantum fluctuations destroy the self trapped state by production of particle pairs of opposite momenta through parametric resonance with the oscillations of the population imbalance observed at small times. We show that through this resonance it is possible, by choosing the parameters of the system appropriately, to produce an interacting 1D bose gas with sharp momentum distribution, and show the conditions that the system must satisfy in order to produce such a state. [Preview Abstract] |
Tuesday, March 17, 2009 3:42PM - 3:54PM |
L16.00007: The Mass of a Spin Vortex, in a Bose Einstein Condensate Ari Turner Ferromagnetic condensates can have both spin-current and charge-current vortices. A moving charge-vortex experiences the Magnus force, perpendicular to its motion, when it moves. This effective ``magnetic field" is so strong that it dominates the inertial term in Newton's law; therefore it is not possible to set a charge-vortex moving at an arbitrary speed relative to the condensate. As we will show, a spin-vortex \emph{can} move ``inertially" through a condensate and resists acceleration with a mass. [Preview Abstract] |
Tuesday, March 17, 2009 3:54PM - 4:06PM |
L16.00008: Unusual states of vortex matter in interacting multicomponent Bose-Einstein condensates Egor Babaev, Eskil Dahl, Asle Sudbo A striking property of a single-component superfluid under rotation, is that a broken symmetry in the order parameter results in a broken translational symmetry, a vortex lattice. If translational symmetry is restored, the phase of the order parameter disorders and the broken symmetry in the order parameter is restored. We show that for interacting mixtures of Bose-condensate (with a dissipationless intercomponent drag), new situations arise. A phase disordered nonsuperfluid component can break translational symmetry in response to rotation due to interaction with a superfluid component. In a different regime instead of a vortex lattice, the system forms a highly disordered tangle which constantly undergoes merger and reconnecting processes involving different types of vortices, with a breakdown of translational symmetry only in a statistical sense. [Preview Abstract] |
Tuesday, March 17, 2009 4:06PM - 4:18PM |
L16.00009: Normal modes of a ring-shaped BEC with vortices Sungjong Woo, Young-Kyun Kwon Recently, a ring-shaped BEC was realized experimentally at NIST and long lasting perpetual current was observed. Using Bogoliubov-de Gennes equations, we have analyzed dynamics of such a non-simply connected rotating condensate system with quantized vortices. Surface modes of a simply connected rotating BEC are known to be associated with driven vortices that can make interactions with the vortex lattice that exists due to the rotation. In our current work, it has been found that stable vortex dipoles or velocity dipoles that do not exist in a normal mode for a simply connected BEC, exist in a non-simply connected case generating ``inner'' surfave modes. The interactions of such inner surface modes with quantized vortices as well as the stability of the perpetual current related to the low lying excitations will be discussed. How the angular dispersion relation changes as a BEC makes a transition from a simply connected to a ring-shaped one will also be presented. [Preview Abstract] |
Tuesday, March 17, 2009 4:18PM - 4:30PM |
L16.00010: Hierarchy of Supercurrents in Multicomponent Atomic Josephson Vortices Vitaliy Kaurov We show that a quasi-1D long atomic Josephson junction [1,2] containing a mixture of BECs can sustain multi-component Josephson vortices (mJV). A new exact soliton solution is given to describe a stationary mJV in the general $N$-component case. Depending on system parameters (scattering lengths, tunneling strengths, and chemical potentials) Josephson supercurrents of different components form a hierarchy according to their intensity and proximity to phase slip. By tuning the parameters it is possible to turn off or on particular currents using the JV -- dark soliton interconversion effect [1,2]. Inside the mJV different components may circulate either in the same or opposite directions resulting in bulk super-counter-flow in the latter case. The weak tunneling limit can be described by a modified Sine-Gordon model. An approximate solution for mJV propagating along the junction is found for the two-component case. The degeneracy of stationary mJV with respect to co-flow or counter-flow configurations is lifted by the uniform motion of mJV. Which configuration is energetically preferable depends on the interspecies scattering length. [1] V. M. Kaurov and A. B. Kuklov, Phys. Rev. A 71, 011601(R) (2005). [2] V. M. Kaurov and A. B. Kuklov, Phys. Rev. A 73, 013627 (2006). [Preview Abstract] |
Tuesday, March 17, 2009 4:30PM - 4:42PM |
L16.00011: Rotating Bose-Einstein condensates at the phase transition point Mahir Hussein, Piet Van Isacker, Klaus Bartschat, Oleg Vorov Here we give analytic description of the phase transitions in the rotating Bose-Einstein condensate of weakly interacting atoms in a magnetic trap [1,2]. The analytic solution allows one to classify the instabilities in the condensates which occur when the rotational speed is increased [3]. In the case of predominantly repulsive interactions, the transition corresponds to the vortex entry the condensate. The transition to the Abrikosov state has follows if the rotational speed is increased further. In the case of predominantly attractive interactions, the transition corresponds to the escape of the condensate from the trap at the critical speed. [1] O. K. Vorov, P. Van Isacker, M. S. Hussein and K. Bartschat, Phys. Rev. Lett. 95, 230406 (2005). [2] O. K. Vorov, M. S. Hussein and P. Van Isacker, Phys. Rev. Lett. 90, 200402 (2003). [3] O. K. Vorov, P. Van Isacker, M. S. Hussein and K. Bartschat, to be submitted to Nature (2007). 1supported by NSF (USA), CEA (France) [Preview Abstract] |
Tuesday, March 17, 2009 4:42PM - 4:54PM |
L16.00012: Strongly Interacting Quantum gases using spin-Coherent state Representation Radha Balakrishnan, Indubala Satija For strongly interacting boson gas, spin-coherent states representation may provide a useful description of the Bose-Einstein Condensate as it encodes fluctuations and depletion. We investigate the the non-linear evolution equation for the order parameter obtained using spin-coherent states. The equation is not of the GPE-type and exhibits local fluctuations and in the limit of small order parameter, it reduces to the GPE equation. We compare and contrast the quasi-particle excitation and the vortex excitations of this system with that of weakly interacting quantum gas described by GPE equation. For a variety of problems, implication of this description of quantum gases will be discussed. [Preview Abstract] |
Tuesday, March 17, 2009 4:54PM - 5:06PM |
L16.00013: Dynamics of spinor condensates near point-group symmetric ground states Gil Refael, Ryan Barnett, Daniel Podolsky The mean-field ground state of spin-S BEC's often exhibits a high degree of symmetry, which only becomes apparent when considering the 2S reciprocal spin-states: coherent spin-states orthogonal to the ground state. Our presentation will concentrate on a description of the dynamics of spinor-condensates using these reciprocal states. First, we will present the resulting hydrodynamic Euler equations, which generalize Mermin-Ho relations to higher spin. Second, we will use the reciprocal states and their hidden point-group symmetry to construct the Goldstone and optical spin-wave modes of the spinor condensates. Finally, we will present a mapping between the spin-wave modes, and the wave functions of electrons in atoms, where the spherical symmetry is degraded by a crystal field. [Preview Abstract] |
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