The alkali Bose condensates are dilute gases of millions of ultracold atoms occupying a single quantum state a few microns across. Are these mesoscopic condensates superfluids? The answer to this question hinges on the response of these finite and highly compressible systems to externally imposed rotation. This talk will describe the nature of the rotating states and the onset of rotation using many-body perturbation theory in the dilute limit for both positive and negative scattering lengths.(D.A. Butts and D.S. Rokhsar, Signatures of rotating Bose-Einstein condensates, to appear, Nature.)
[SC06.02] Expansion of a droplet of Bose-Einstein condensate
Boris Laikhtman, Dror Sagi (Hebrew University, Jerusalem, Israel)
The free expansion of a Bose-Einstein condensate droplet is studied. Basically we mean the exciton condensate in Cu_2O but the most of the results can be applied also to the trapped Bose condensate of alkali atoms. The expansion leads to a formation of a shock wave. The deformation potential interaction with phonons is very weak and cannot prevent the formation of the shock wave. The expanding condensate droplet appears to be unstable with respect to creation of normal excitations. This instability leads to depletion of the condensate. The depletion time is estimated.
[SC06.03] Real-space Condensation in a Dilute Bose Gas at Low Temperature
I. O. Kulik, B. Tanatar (Department of Physics, Bilkent University, Ankara, Turkey)
We consider the properties of Bose gas in a thermal environment (blackbody radiation) at temperature T_1 simultaneously interacting with an ``optical molasses'' at much lower temperature T_2 produced by laser irradiation. In a ``trap'' - which is choosen for simplicity as a radial parabolic well - particles condense in the phase space at point r=0, p= 0, thus showing also a condensation to a globular structure in real space. Quantization of particle motion in a well wipes out sharp transition at T_c but supports the distribution of radial particle density \rho(r) peaked at r=0 (a real-space condensate) as well as the phase-space Wigner distribution W(r, p) peaked at r=0 and p=0. We also resolve the seeming paradox of giant particle-number fluctuation in a grand canonical ensemble generally accepted for the treatment of Bose-Einstein condensation in systems of fixed number of particles.
[SC06.04] Stochastic Dynamics of the Condensate in a Weakly Non-Ideal Bose Fluid
R. \vSá\vsik, S. Habib, A. R. Bishop (Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545)
We present a semi-classical phenomenological theory of stochastic dynamics of the Bose condensate in contact with a thermal heat bath. The condensate wavefunction \psi(r,t) is treated as a classical field whose elementary excitations in equilibrium have a Bose-Einstein distribution. The equation of motion for \psi(r,t) involves a non-local random force with a length scale equal to the phonon thermal length, \hbar c/(k_BT), where c is the speed of sound in the superfluid. In the underdamped limit this equation becomes equivalent to the Gross-Pitaevskii equation.
[SC06.05] Spin Textures of Spin-1 Bose Condensates in Optical Traps
Cristian V. Ciobanu, Tin-Lun Ho (Dept. of Physics, The Ohio State University)
We have studied the spin texture of F=1 spinor Bose condensates with both ferromagnetic and antiferromagnetic interactions in anisotropic optical traps. For a wide range of anisotropy, the system can have Skyrmion textures which generate persistent currents through spin-gauge effects. Effects of external rotations have also been studied.
[SC06.06] Solution of the time-dependent, fully three dimensional GP equation
J. L. V. Lewandowski, M. Gulacsi (Australian National University, Canberra, Australia)
The first numerical solution of the time-dependent, fully three dimensional Gross-Pitaevskii (GP) equation in a cylindrical coordinates is presented. A second-order accurate numerical method satisfying the specific symmetries of the problem is used to study the stability and properties of a Bose-Einstein condensate (BEC). In particular, the time evolution of asymmetric BECs has also been studied.
[SC06.07] Bose-Einstein Condensation and Single Particle Orbitals in Trapped Hard Sphere Bosons
Jonathan L. DuBois, Henry R. Glyde (University of Delaware)
Several properties of trapped hard sphere bosons are evaluated using variational Monte Carlo techniques. A trial wave function composed of a renormalized single particle gaussian and a hard sphere Jastrow function for pair correlations is used to study the sensitivity of condensate and non-condensate properties to the hard sphere radius and the number of particles. Special attention is given to diagonalizing the one body density matrix and obtaining the corresponding single particle natural orbitals and their occupation numbers for the system. The condensate wave function and condensate fraction are then obtained from the lowest energy single particle orbital. The effect of interaction on other quantities such as the ground state energy, the mean radius, and the momentum distribution are estimated as well. Results are compared with solutions of the Gross-Pitaevskii equation in the dilute limit and the slave boson approach in the dense regime.
[SC06.08] Spinor F=2 Bose Condensates
Sungkip Yip (Center for Theoretical Sciences, Hinschu, Taiwan), Cristian V. Ciobanu, Tin-Lun Ho (Dept.of Physics, The Ohio State University)
We have obtained the general phase diagram of F=2 spinor Bose condensates in optical traps including quadratic Zeeman effect. In zero field, there are only three phases possible, one ferromagnetic and two non-magnetic. Our method also shows a remarkable connection between the structures of spinor Bose condensates, large spin s-wave Cooper pairs, and singlet superconductors of arbitrary angular momentum.
[SC06.09] Broken Symmetries in Binary Bose-Einstein Condensate Mixtures of Weakly and Strongly Segregated Phases
S.T. Chui (University of Delaware, USA), P Ao (Umea University, SWEDEN)
We find the absence of cylindrical symmetry in the density difference of a binary mixture of Bose-Einstein condensates in traps in the phase segregated regime. We further analize it in a mean-field manner as a function of the mutual repulsive interaction strength, and find that there are two distinct phases in the phase segregated regime: the weakly segregated phase characterized by a `penetration depth' and the strongly segregated phase characterized by a healing length. In the weakly segregated phase the symmetry of the shape of each condensate will not take that of the trap because of the finite surface tension, but their total density profile still does. In the strongly segregated phase even the total density profile takes a different symmetry from that of the trap because of the mutual exclusion of the condensates. The floating of a condensate droplet in the phase segregated regime and The lower critical condensate-atom number to observe the complete phase segregation is discussed.
[SC06.10] Droplets of He3-He4 mixtures
Hualin Shi, S. T. Chui (Bartol Research Institute, Univ. of Delaware, Newark, DE 19716)
We describe simulation results for droplets of He3-He4
mixtures. The effect of the phase segragation on the shape
of the droplet will be discussed. For clouds of Alkali atom
Bose condensates, we recently discovered that the shape of
the symmetry can change. (S. T. Chui, P. Ao and B. Tanatar,
Phys. Rev. A). The present system is strongly interacting
whereas the BEC system is weakly interacting. The similarity
and differences of the present system from clouds of Alkali
atom Bose condensates will be considered. The effect of
droplet size and relative concentration on the symmetry of
the droplet will be mentioned.
[SC06.11] Supersolid and Insulating Phases of Bose Atoms in Optical Lattices
Cristian V. Ciobanu, Tin-Lun Ho (Dept. of Physics, The Ohio State University)
We have shown that the ground state of a Bose system in an optical lattice typically consists of layers of supersolid and insulating phases. We have studied the structure and dynamics of these phases.