Bulletin of the American Physical Society
2006 37th Meeting of the Division of Atomic, Molecular and Optical Physics
Tuesday–Saturday, May 16–20, 2006; Knoxville, TN
Session L3: BEC Vortices and Spinor Condensates |
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Chair: James Williams, National Institute of Standards and Technology Room: Knoxville Convention Center 301D |
Thursday, May 18, 2006 10:30AM - 10:42AM |
L3.00001: Vortex pinning in a fast rotating Bose-Einstein condensate Shihkuang Tung, Volker Schweikhard, Eric Cornell We present the first experiment on vortex pinning in a fast rotating Bose-Einstein condensate. The attractive pinning potential for the vortices is constructed by a two-dimensional optical lattice, centered and co-rotating with a rotating BEC. We report the results of vortex pinning with two different applied optical lattices, triangular and square, respectively. When a triangular optical lattice is applied, the angular orientation of the vortex lattice locks to the optical lattice. A pinning phase diagram is mapped out as a function of optical lattice rotation rate and optical potential depth. In another experiment when a square optical lattice is applied, we observe the structural phase transition from a triangular vortex lattice to a pinned square vortex lattice. The transition takes place via a ``half pinned'' phase where one plane of vortices locks to the optical lattice while the structure remains close to triangular. With increasing optical potential depth the lattice structure changes to the fully pinned square structure. We again present a phase diagram for this transition. [Preview Abstract] |
Thursday, May 18, 2006 10:42AM - 10:54AM |
L3.00002: Bragg Spectroscopy of Vortex Lattices in Bose-Einstein condensates Sergio R. Muniz, Devang S. Naik, Mishkatul Bhattacharya, Chandra Raman We have measured the velocity field of a vortex lattice within a sodium Bose-Einstein condensate using Bragg scattering. The phase gradient of the macroscopic wavefunction was mapped into the spatial structure of the diffracted atom cloud, allowing for single shot measurement of the rotation parameters. A combination of spectral and spatial information yields a complete description of the superfluid flow, coarse-grained over the lattice structure, including direct and independent measurements of the rate and sense of rotation. Signatures of the microscopic quantum rotation have also been observed. [Preview Abstract] |
Thursday, May 18, 2006 10:54AM - 11:06AM |
L3.00003: Phase transitions in rotating Bose-Einstein condensates. Oleg Vorov, Klaus Bartschat, P. Van Isacker, M. Hussein Phase transitions, or abrupt changes of state under a smooth variation of external conditions, are of great interest in natural sciences. A remarkable property of a Bose-Einstein superfluid in a rotating bucket is its change to a vortex state once the bucket's rotational velocity exceeds a critical value. This transition to the Abrikosov state has been observed in cold atomic gases [1]. Such critical behavior is very sensitive to the interaction between the particles in the condensate [2,3]. We give an analytic description [4] of the first phase-transition point and classify the types of the corresponding instabilities that depend on the interaction. This toy model of a continuous phase transition predicts the same behavior patterns for all systems governed by a similar energy functional. [1] V. Schweikhard, I. Coddington, P. Engels, V. P. Mogendorff, and E. A. Cornell, Phys. Rev. Lett. {\bf 92}, 040404 (2004). [2] O. K. Vorov, P. Van Isacker, M. S. Hussein and K. Bartschat, Phys. Rev. Lett. {\bf 95}, 230406 (2005). [3] O. K. Vorov, M. S. Hussein and P. Van Isacker, Phys. Rev. Lett. {\bf 90}, 200402 (2003). [4] O. K. Vorov, P. Van Isacker, M. S. Hussein and K. Bartschat, submitted to Nature (2006). [Preview Abstract] |
Thursday, May 18, 2006 11:06AM - 11:18AM |
L3.00004: Stability of Ring Dark Solitons in Bose-Einstein Condensates Mark Edwards, Lincoln Carr, Charles W. Clark Bose-Einstein condensates confined in a cylindrical ``can'' potential (Prince Albert potential) admit vortex-like solutions of the time-independent Gross-Pitaevskii (GP) equation that consist of a number of nodal rings concentric with the vortex line. The radius of the can must coincide with one of the nodal rings in order that the state be a stationary solution of the GP equation. If a phase imprint consisting of a single jump at one of the intermediate nodal rings is applied, a ring-shaped dark soliton is created which exhibits oscillatory radial motion. We have studied the stability of this time-dependent state by performing a partial-wave analysis of the solution of the time- dependent GP equation and deriving the coupled time-dependent equations of motion for the partial waves and by performing a Bogoliubov analysis. We have used these equations to study the effects of a ring phase imprint that is not concentric with the vortex line and the rate of diffusion of a single ring soliton when partial waves of neighboring winding number are seeded with a small amount of population. We also show the connection with the Bogoliubov analysis. [Preview Abstract] |
Thursday, May 18, 2006 11:18AM - 11:30AM |
L3.00005: Fragmentation and Phase Manipulation Studies of Bose-Einstein Condensates using Computer-Generated Holograms Brian Anderson, David Scherer, Chad Weiler, Tyler Neely Computer-generated holograms (CGHs) and diffractive optical elements can be used as tools to manipulate Bose-Einstein condensates with tailored optical fields of arbitrary profiles. Using CGHs designed and created at the College of Optical Sciences, we are investigating phase manipulation and fragmentation dynamics of Bose-Einstein condensates in combined optical and magnetic trapping fields. We will briefly summarize our CGH creation technique and report on the progress of our experiments with Rb-87 Bose-Einstein condensates. [Preview Abstract] |
Thursday, May 18, 2006 11:30AM - 11:42AM |
L3.00006: Normal modes of vortex sheets in a BEC - connection of Tkachenko modes with hydrodynamic excitations Sungjong Woo, Stephen Choi, Leslie Baksmaty, Nicholas Bigelow It is well known that quantized vortices are formed in a rotating Bose-Einstein condensate (BEC). If there are more than one species in a BEC described by seperate order parameters, it has been found theoretically that vortex sheets are formed which are different from the ordinary triangular vortex lattice. In our research, the dynamics of vortex sheets has been studied. Differently from the the traditional treatment of the vortex dynamics, we start with an idea that the precessional motion of a vortex in a Tkachenko mode can be understood as a local hydrodynamic excitation confined within a vortex. We find that the excitation of a vortex sheet is a connecting route between Tkachenko modes of the vortices and the hydrodynamic modes of the underlying superfluid. Energy spectrum of the Tkachenko modes and hydrodynamic excitations and how they are related through vortex sheets will be discussed. [Preview Abstract] |
Thursday, May 18, 2006 11:42AM - 11:54AM |
L3.00007: Single-Mode Approximation and Dynamical Localization in a Ferromagnetic Spin-1 Condensate Q. Qin, E.M. Bookjans, P.F. Griffin, M.-S. Chang, M.S. Chapman Bose condensates with internal degrees of freedom offer rich quantum dynamics due to the nonlinear spin-spin interactions and the vector properties of the condensate order parameter. Recent experiments on spin-1 condensates have revealed that the internal spin-changing collisions lead to coherent spin mixing [1]. When the size of the condensate is smaller than the spin healing length, all three Zeeman components will have the same spatial wavefunction, a condition referred to as the single-mode approximation (SMA). In this case, the coherent spin mixing in a spin-1 condensate represents a nonlinear Josephson oscillator, similar to two weakly-linked superconductors. This is an ideal system for observing Shapiro levels or the dynamical localization of the spinor system. We will report the most recent progress of our experiment.\newline \newline [1] M.-S. Chang, et al., Nat. Phys., \textbf{1}, 111 (2001) [Preview Abstract] |
Thursday, May 18, 2006 11:54AM - 12:06PM |
L3.00008: Nonadiabatic production of spinor condensates with a QUIC trap Peng Zhang, Zhan Xu, Li You A recent experiment [Xiu-Quan Ma {\it et al.}, Chin. Phys. Lett. {\bf 22}, 1106 (2005)] reported the observation of a multi-component spinor condensate when the magnetic field of a QUIC trap containing a spin polarized condensate was switched off. Our theoretical study show that this phenomena can be described within a general framework of the nonadiabatic Landau-Zener transition theory. We will discuss the population transfers at the zero field level crossing for this interesting case involving more than two levels, and provide a detailed understanding of the relevant nonadiabatic behavior. [Preview Abstract] |
Thursday, May 18, 2006 12:06PM - 12:18PM |
L3.00009: Spontaneous Symmetry Breaking in a Quenched Ferromagnetic Spinor Condensate Mukund Vengalattore, Lorraine Sadler, James Higbie, Sabrina Leslie, Dan Stamper-Kurn We observe spontaneous symmetry breaking in a F=1 $^{87}$Rb spinor condensate after it is quenched past a ``polar'' to ferromagnetic quantum phase transition. As an initially unmagnetized condensate is brought to low magnetic field, nondestructive phase contrast images reveal the spontaneous formation of ferromagnetic domains with a characteristic length scale of 6 microns, much smaller than the size of the condensate. Concurrent with the formation of these domains, we also observe topological defects which we characterize as singly charged spin vortices. The time scale of the evolution is well described by a dynamical instability resulting from a competition between the quadratic Zeeman energy and the spin dependent interaction energy. Recent progress from this study will be presented. [Preview Abstract] |
Thursday, May 18, 2006 12:18PM - 12:30PM |
L3.00010: Magnetometry with Spinor Condensates Sabrina Leslie, James Higbie, Mukund Vengalattore, Lorraine Sadler, Dan Stamper-Kurn We demonstrate the use an F=1 spinor Bose Einstein condensate as a magnetometer with high spatial resolution. The magnetization profile of the condensate is non-destructively imaged and from a sequence of such images, the temporal phase of a Larmor precessing transversely magnetized spinor condensate is extracted. Interactions in a spinor condensate are rotationally symmetric, and thus the precession frequency is expected to be density independent. Comparison of this phase with a local oscillator after a coherent evolution yields a spatially-resolved measurement of the magnetic field. Preliminary experiments have been performed in which a local magnetic field is applied optically to part of the condensate using the spin-dependence of the AC Stark Shift. The present resolution of this magnetometer is 9nG for a spatial resolution of 6 microns, or 144 pG should the condensate be used as a single-channel magnetometer. This method is best suited for mapping magnetic field inhomogeneities with high spatial resolution, ultimately rivaling the performance of spatially-scanned SQUID magnetometers. [Preview Abstract] |
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