Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session X9: Focus Session: Spinor Condensates and Dipolar Gases |
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Sponsoring Units: DAMOP Chair: Chris Greene, University of Colorado Room: Morial Convention Center RO7 |
Friday, March 14, 2008 8:00AM - 8:12AM |
X9.00001: Amplification of quantum fluctuations across a quantum phase transition in a spinor BEC Sabrina Leslie, Jennie Guzman, Mukund Vengalattore, Dan Stamper-Kurn We study the amplification of quantum fluctuations in a $^{87}$Rb spinor BEC that is rapidly quenched from its paramagnetic phase to its ferromagnetic phase. By characterizing the onset of spontaneous ferromagnetism and the amplification properties of the spinor condensate, we probe the initial quantum fluctuations from which the resulting structures evolve. To characterize the spinor condensate as an amplifier, we temporally and spatially resolve the evolution of the vector magnetization profile as a function of the end point of the quench. In particular, we describe the formation of transversely magnetized domains and vortices as a function of the end point. [Preview Abstract] |
Friday, March 14, 2008 8:12AM - 8:24AM |
X9.00002: Equilibrium phases of a dipolar spinor Bose gas Mukund Vengalattore, S. R. Leslie, J. Guzman, C. Smallwood, D. M. Stamper-Kurn We investigate the effect of magnetic dipole interactions in determining the properties of $F=1$ spinor Bose gases of $^{87}$Rb. Due to the competition between the local ferromagnetic interaction and the long-range, anisotropic dipole interaction, we observe the spontaneous formation of modulated spin domains that exhibit crystalline order. The formation of this modulated spin texture is accompanied by the creation of spin vortices in this dipolar superfluid. We observe this modulated phase both as an equilibrium phenomenon by cooling an incoherent thermal spinor gas, and as a result of a dynamical instability in a pure transversely magnetized spinor condensate. We clarify the crucial role played by dipolar interactions in the creation of the crystalline phase in the spinor condensate and study the finite temperature phase diagram of this dipolar quantum fluid. [Preview Abstract] |
Friday, March 14, 2008 8:24AM - 8:36AM |
X9.00003: Dynamical instability of the XY spiral state of ferromagnetic condensates Robert Cherng, Vladimir Gritsev, Dan Stamper-Kurn, Eugene Demler We calculate the spectrum of collective excitations of the XY spiral state prepared adiabatically or suddenly from a uniform ferromagnetic F = 1 condensate. For spiral wavevectors past a critical value, spin wave excitation energies become imaginary indicating a dynamical instability. We construct phase diagrams as functions of spiral wavevector and quadratic Zeeman energy. [Preview Abstract] |
Friday, March 14, 2008 8:36AM - 8:48AM |
X9.00004: Spin Nematics and Quantum Fluctuation-Controlled Coherent Spin Dynamics of Hyperfine Spin F=2 Cold Atoms Jun Liang Song, Gordon Semenoff, Fei Zhou We show that quantum fluctuations lift the accidental continuous degeneracy that was found in the mean field analysis of spin nematic states of hyperfine spin F=2 $^{87}$Rb. Two distinct spin nematic states with higher symmetries are selected out depending on scattering lengths: a uniaxial spin nematic and a biaxial spin nematic. Recently we also study coherent spin dynamics mainly driven by quantum fluctuations. Unlike the usual mean-field driven dynamics, quantum fluctuation-controlled spin dynamics are sensible to the variation of fluctuations and the potential induced by quantum fluctuations can be tuned by four or five orders of magnitude in optical lattices. These dynamics have unique dependence on quadratic Zeeman fields and potential depth in optical lattices. We find that although these dynamics are difficult to observe in traps, it is possible to observe them in optical lattices; particularly they can survive in F=2 $^{87}$Rb condensates with a relatively short life time. [Preview Abstract] |
Friday, March 14, 2008 8:48AM - 9:00AM |
X9.00005: Nematic order by disorder in spin-2 BECs Ryan Barnett, Ari Turner, Eugene Demler, Ashvin Vishwanath The effect of quantum and thermal fluctuations on the phase diagram of spin-2 BECs is examined. They are found to play an important role in the nematic part of the phase diagram, where a mean-field treatment of two-body interactions is unable to lift the accidental degeneracy between nematic states. Quantum and thermal fluctuations resolve this degeneracy, selecting the uniaxial nematic state, for scattering lengths $a_4$ greater than $a_2$, and the square biaxial nematic state for $a_4$ less than $a_2$. Paradoxically, the fluctuation induced order is stronger at higher temperatures, for a range of temperatures below $T_c$. For the experimentally relevant cases of spin-2 $^{87}$Rb and $^{23}$Na, we argue that such fluctuations could successfully compete against other effects like the quadratic Zeeman field, and stabilize the uniaxial phase for experimentally realistic conditions. A continuous transition of the Ising type from uniaxial to square biaxial order is predicted on raising the magnetic field. These systems present a promising experimental opportunity to realize the `order by disorder' phenomenon. [Preview Abstract] |
Friday, March 14, 2008 9:00AM - 9:12AM |
X9.00006: ABSTRACT WITHDRAWN |
Friday, March 14, 2008 9:12AM - 9:48AM |
X9.00007: Ultracold dipolar gases -- challenge for Experiments and Theory Invited Speaker: Recent experimental progress in trapping and cooling of molecular gases boosts an interest to the interdisciplinary field of quantum gases with dominant dipole-dipole interactions. An unprecedented level of experimental control together with specific physical properties of the dipole-dipole interaction provides a unique possibility to find new physical phenomena and practical applications. In this talk, recent achievements in studies of ultracold dipolar gases, both fermionic and bosonic, are presented. We focus our attention on many-body properties of such systems and discuss how the characteristic features of the dipole-dipole interaction: long range and anisotropy, affect their collective behavior and result in novel macroscopic quantum phenomena. [Preview Abstract] |
Friday, March 14, 2008 9:48AM - 10:00AM |
X9.00008: Spin-orbit interaction effects in cold atomic systems Tudor Stanescu, Victor Galitski We propose a scheme for the realization of spin-orbit interaction in cold atomic systems. We show that, in a system of trapped multi-level atoms moving in the presence of spatially modulated laser fields, the atom-laser interaction generates an emergent pseudo-spin-1/2 degree of freedom that couples to the momentum, leading to an effective spin-orbit interaction. The parameters of the spin-orbit coupling can be modified by controlling the laser fields. Atomic spin-orbit interacting systems open the possibility of studying new effects that are not usually considered, or not accessible in solid state systems. We consider explicitly the problem of strongly non-equilibrium spin dynamics by studying the evolution of an initially spin-polarized Fermi gas in a two-dimensional harmonic trap. We derive the non-equilibrium behavior of the polarization and show that it is characterized by periodic echoes with a frequency equal to the trapping frequency. We also consider a system of multi-level Bose atoms. In the presence of spin-orbit coupling, the single-particle band structure is generally anisotropic and contains two minima at finite momenta. At low temperatures, the bosons condense into these states, leading to a new type of Bose-Einstein condensate. [Preview Abstract] |
Friday, March 14, 2008 10:00AM - 10:12AM |
X9.00009: Dipolar bosons in an array of one-dimensional tubes Julia S. Meyer, Corinna Kollath, Thierry Giamarchi Ultra-cold atomic and molecular gases offer a unique possibility to realize a range of novel interacting many-body systems. While in solid state systems electrons interact via the long-range Coulomb interactions, the interactions in cold gases are essentially local. However, the use of dipolar atoms or molecules allows one to surmount this limitation. We investigate bosonic atoms or molecules interacting via dipolar interactions in a planar array of one-dimensional tubes. In the situation where the dipoles are oriented perpendicular to the tubes by an external field, various quantum phases can be realized by varying the strength of the interactions and the orientation of the dipoles with respect to the plane of the array. We find a `sliding Luttinger liquid' phase in which the tubes remain Luttinger liquids and two-dimensional charge density wave ordered phases with different kinds of order. In particular, a stripe phase in which the bosons in different tubes are aligned as well as a checkerboard phase occur. [Preview Abstract] |
Friday, March 14, 2008 10:12AM - 10:24AM |
X9.00010: Phase space deformation of dipolar Fermi gas Han Pu, Takahiko Miyakawa, Takaaki Sogo, Hong Lu We consider a system of quantum degenerate spin polarized fermions in a harmonic trap at zero temperature, interacting via dipole-dipole forces. Under the semi-classical framework, we introduce a variational Wigner distribution function to characterize the deformation and compression of the Fermi gas in phase space and use it to examine the stability of the system. We emphasize the important roles played by the Fock exchange term of the dipolar interaction which results in a non-spherical Fermi surface. [Preview Abstract] |
Friday, March 14, 2008 10:24AM - 10:36AM |
X9.00011: ABSTRACT WITHDRAWN |
Friday, March 14, 2008 10:36AM - 10:48AM |
X9.00012: Towards Microwave Trapping of Cold Polar Molecules Y.-C. Chen, C.-C. Hsieh, T.-S. Ku, P. Dwivedi, R. Ho We describe our progress on production and trapping of cold SrF molecules. Specifically, we generate the SrF molecules by laser ablation of its solid precursor. We use helium buffer gas cooling as the first cooling stage to cool molecules down to a few Kelvin. To guide the generated cold molecules to ultrahigh vacuum region for further spectroscopic studies and trapping, we are also developing the electrostatic guiding of molecules. The experimental results will be presented. For a second-stage cooling in order to cool molecules down to ultracold regime, we plan to perform the sympathetic cooling of molecules with ultracold cesium atoms in a microwave trap. We have succeeded to build a microwave trap based on a high-power microwave Fabry-Perot resonator. We can couple 1.4 kW power into the cavity with a coupling efficiency more than 80{\%} under locked conditions. The trap depth for the absolute ground state of SrF molecules is 300mK. The design and performance as well as future improvements will be discussed in details. [Preview Abstract] |
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