Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session A31: Spinor Degrees of Freedom and Rotation in Quantum Gases 
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Sponsoring Units: DAMOP Chair: Richard Scalettar, University of California, Davis Room: E141 
Monday, March 15, 2010 8:00AM  8:12AM 
A31.00001: Spin waves in a spin1 normal Bose gas Stefan Natu, Erich Mueller We present a theory of spin waves in a noncondensed gas of spin1 bosons: providing both analytic calculations of the linear theory, and full numerical simulations of the nonlinear response. We highlight the role of spindependent contact interactions in the dynamics of a thermal gas. Although these interactions are small compared to the thermal energy, they set the scale for low energy long wavelength spin waves. In particular, we find that the polar state of $^{87}$Rb is unstable to collisional mixing of magnetic sublevels even in the normal state. We augment our analytic calculations by providing full numerical simulations of a trapped gas, explicitly demonstrating this instability. Further we show that for strong enough antiferromagnetic interactions, the polar gas is unstable. Finally we explore coherent population dynamics in a collisionless transversely polarized gas. [Preview Abstract] 
Monday, March 15, 2010 8:12AM  8:24AM 
A31.00002: Low energy dynamics of spinor condensates Austen Lamacraft We present a derivation of the low energy Lagrangian governing the dynamics of the spin degrees of freedom in a spinor Bose condensate, for any phase in which the average magnetization vanishes. This includes all phases found within meanfield treatments except for the ferromagnet, for which the low energy dynamics has been discussed previously. The Lagrangian takes the form of a sigma model for the rotation matrix describing the local orientation of the spin state of the gas. [Preview Abstract] 
Monday, March 15, 2010 8:24AM  8:36AM 
A31.00003: Isentropes of spin1 bosons in an optical lattice Khan W. Mahmud, George G. Batrouni, Richard T. Scalettar We study the effects of adiabatic ramping of optical lattices on the temperature of spin1 bosons in a homogeneous lattice. Using meanfield theory, we present the isentropes in the temperatureinteraction strength ($T,U_0$) plane for ferromagnetic, antiferromagnetic, and zero spin couplings. Following the isentropic lines, temperature changes can be determined during adiabatic loading of current experiments. We show that the heatingcooling separatrix lies on the superfluidMott phase boundary with cooling occuring within the superfluid and heating in the Mott insulator, and quantify the effects of spin coupling on the heating rate. We find that the meanfield isentropes for low initial entropy terminate at the superfluidMott insulator phase boundary. [Preview Abstract] 
Monday, March 15, 2010 8:36AM  8:48AM 
A31.00004: Spin drag in noncondensed Bose gases Rembert Duine We show how timedependent magnetic fields lead to spin motive forces and spin drag in a spinor Bose gas. We propose to observe these effects in a toroidal trap and analyze this particular proposal in some detail. In the linearresponse regime we define a transport coefficient that is analogous to the usual drag resistivity in electron bilayer systems. Due to Bose enhancement of atomatom scattering, this coefficient strongly increases as temperature is lowered. We also investigate the effects of heating. [Preview Abstract] 
Monday, March 15, 2010 8:48AM  9:00AM 
A31.00005: Mott Insulator to Superfluid transition with two component bosons Barbara CapogrossoSansone, Marco Guglielmino, Vittorio Penna We consider the Mott insulator to superfluid transition of one component in the presence of a superfluid second component. We study how Mott lobes vary with changing density of the superfluid species and interspecies interaction. [Preview Abstract] 
Monday, March 15, 2010 9:00AM  9:12AM 
A31.00006: Thermodynamic properties of twocomponent cold Fermi gases with bound states Naoyuki Sakumichi, Norio Kawakami, Masahito Ueda We address the thermodynamics of a twocomponent cold Fermi gas with shortrange interaction. In the BEC region of the BCSBEC crossover the fermionic particles form bosonic dimers as the twoparticle bound states. We focus on the fermionic properties of the particles which constitute the dimers. To this end, we use the LeeYang quantum cluster expansion method, which enables us to expand the logarithm of the grand partition function in a power series of fugacity. By calculating the fourthorder contribution in fugacity we elucidate how the thermodynamic properties are affected by the quantumstatistical exchange effect between two fermionic particles that belong to different bosonic dimers. Furthermore, we extend the method to take into account the effect of the monomerdimer and dimerdimer scatterings and discuss the corresponding scattering length. [Preview Abstract] 
Monday, March 15, 2010 9:12AM  9:24AM 
A31.00007: Exotic paired states with anisotropic spindependent Fermi surfaces Adrian Feiguin, M. P. A. Fisher We propose a model for realizing exotic paired states in cold atomic Fermi gases. By using a {\it spin dependent} optical lattice it is possible to engineer spatially anisotropic Fermi surfaces for each hyperfine species, that are rotated 90 degrees with respect to one another. We consider a balanced population of the fermions with an attractive interaction. We explore the BCS mean field phase diagram as a function of the anisotropy, density, and interaction strength, and find the existence of an unusual paired superfluid state with coexisting pockets of gapless unpaired carriers. This state is a relative of the Sarma or breached pair states in polarized mixtures, but in our case the Fermi gas is unpolarized. We also propose the possible existence of an exotic paired ``Cooperpair BoseMetal" (CPBM) phase, which has a gap for single fermion excitations but gapless and uncondensed ``Cooper pair" excitations residing on a ``Bosesurface" in momentum space. We extend our study of the model to a ladder geometry by using the density matrix renormalization group method, and we unveil a phase diagram with paired states that reveal a striking resemblance to the physics of hardcore bosons with a frustrating ringexchange term. [Preview Abstract] 

A31.00008: ABSTRACT WITHDRAWN 
Monday, March 15, 2010 9:36AM  9:48AM 
A31.00009: Magnetic phase diagram of a spin1 condensate in two dimensions with dipole interaction Jonas Kj\"{a}ll, Andrew Essin, Joel E. Moore Several new features arise in the groundstate phase diagram of a spin1 condensate trapped in an optical trap when the magnetic dipole interaction between the atoms is taken into account along with confinement and spin precession. The boundaries between the regions of ferromagnetic and polar phases move as the dipole strength is varied and the ferromagnetic phases can be modulated. The magnetization of the ferromagnetic phase perpendicular to the field becomes modulated as a helix winding around the magnetic field direction, with a wavelength inversely proportional to the dipole strength. This modulation should be observable for current experimental parameters in $^{87}$Rb. Hence the much sought supersolid state, with broken continuous translation invariance in one direction and broken global $U(1)$ invariance, occurs generically as a metastable state in this system as a result of dipole interaction. The ferromagnetic state parallel to the applied magnetic field becomes striped in a finite system at strong dipolar coupling. [Preview Abstract] 
Monday, March 15, 2010 9:48AM  10:00AM 
A31.00010: Quantum Phases of BoseEinstein condensates in rotating optical lattice Sankalpa Ghosh, Rashi Sachdeva , Sonika Johri Ultra cold BoseEintstein condensate of alkali atoms loaded in a deep optical lattice shows transition from the Superfluid(SF) phase to Mott Insulator(MI) Phase as the depth of the lattice potential is varied. When these phases are exposed to the effect of a rotation which is equivalent to apply the effect of of a magnetic field to such neutral atomic condensate, novel vortex lattice phases arises. The nature of the such vortex lattice phases strongly depend upon the strength and range of the interaction as well as the strength of the rotation. Whether the system is in deep inside the superfluid phase or near the SFMI transition boundary strongly influences the structure of the vortex lattice or nature of the vortex core. Using mean field Gutzwiller ansatz and imposing various type of boundary conditions that mimic a number of external applied potential we study such vortex and vortex lattice phase diagram for such BoseEinestein condensates in such rotated optical lattice. We also point out how experimentally one should be able to identify such novel collective phases of vortices. [Preview Abstract] 

A31.00011: ABSTRACT WITHDRAWN 
Monday, March 15, 2010 10:12AM  10:24AM 
A31.00012: Solvable model of the second order phase transition in rotating BEC Mahir Hussein, Klaus Bartschat, Pieter Van Isacker, Oleg Vorov We solve analytically a model of the secondorder phase transitions that arises in the context of rotating BoseEinstein condensate of cold atoms in a magnetic trap, interacting via twobody forces [1,2]. The 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 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.\\[4pt] [1] O. K. Vorov, P. Van Isacker, M. S. Hussein and K. Bartschat, Phys. Rev. Lett. 95, 230406 (2005).\\[0pt] [2] O. K. Vorov, M. S. Hussein and P. Van Isacker, Phys. Rev. Lett. 90, 200402 (2003).\\[0pt] [3] O. K. Vorov, P. Van Isacker, M. S. Hussein and K. Bartschat, to be submitted to Nature (2009). [Preview Abstract] 
Monday, March 15, 2010 10:24AM  10:36AM 
A31.00013: Hidden vortex lattices in a thermally paired superfluid Egor Babaev, Eskil Dahl, Asle Sudbo We study the evolution of rotational response of a twocomponent superfluid mixture with intercomponent drag interaction, as the system undergoes a transition into a paired phase at finite temperature. We find that the transition into a paired state manifests itself in a change of (i) vortex lattice symmetry, and (ii) nature of vortex state. Instead of a usual vortex lattice, the system forms a highly disordered vortex tangle which constantly undergoes merger and reconnecting processes involving different types of vortices, with a breakdown of translational symmetry only in a statistical sense. We discuss how it can complicate an observation of a paired bosonic state via rotational response. [Preview Abstract] 
Monday, March 15, 2010 10:36AM  10:48AM 
A31.00014: Unusual states of vortex matter in mixtures of BoseEinstein Condensates on rotating optical lattices Asle Sudbo, Eskil Dahl, Egor Babaev A striking property of a singlecomponent 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 BoseCondensate mixtures on optical lattices (which may possess a negative dissipationless intercomponent drag), a new situation arises. A phase disordered nonsuperfluid component can break translational symmetry in response to rotation due to interaction with a superfluid component. This state is a modulated vortex liquid which breaks translational symmetry in the direction transverse to the rotation vector. [Preview Abstract] 
Monday, March 15, 2010 10:48AM  11:00AM 
A31.00015: Coreless vorticity in multicomponent Bose and Fermi superfluids Gianluigi Catelani, Emil Yuzbashyan We consider quantized vortices in twocomponent BoseEinstein condensates and threecomponent Fermi gases with attractive interactions. In these systems, the vortex core can be either empty (normal in the fermion case) or filled with another superfluid. We determine critical values of the parameters  chemical potentials, scattering lengths and, for Fermi gases, temperature  at which a phase transition between the two types of vortices occurs. Population imbalance can lead to superfluid core (coreless) vorticity in multicomponent superfluids which otherwise support only usual vortices. For multicomponent Fermi gases, we construct the phase diagram including regions of coreless vorticity. We extend our results to trapped bosons and fermions using an appropriate local approximation, which goes beyond the usual ThomasFermi approximation for trapped bosons. [Preview Abstract] 
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