5,577 research outputs found
Phase space deformation of a trapped dipolar Fermi gas
We consider a system of quantum degenerate spin polarized fermions in a
harmonic trap at zero temperature, interacting via dipole-dipole forces. We
introduce a variational Wigner function to describe 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.Comment: 5 pages, 5 figure
Making vortices in dipolar spinor condensates via rapid adiabatic passage
We propose to the create vortices in spin-1 condensates via magnetic
dipole-dipole interaction. Starting with a polarized condensate prepared under
large axial magnetic field, we show that by gradually inverting the field,
population transfer among different spin states can be realized in a controlled
manner. Under optimal condition, we generate a doubly quantized vortex state
containing nearly all atoms in the condensate. The resulting vortex state is a
direct manifestation of the dipole-dipole interaction and spin textures in
spinor condensates. We also point out that the whole process can be
qualitatively described by a simple rapid adiabatic passage model.Comment: 4 pages, 4 figure
Self-trapping of a Fermi super-fluid in a double-well potential in the BEC-unitarity crossover
We derive a generalized Gross-Pitaevskii density-functional equation
appropriate to study the Bose-Einstein condensate (BEC) of dimers formed of
singlet spin-half Fermi pairs in the BEC-unitarity crossover while the
dimer-dimer scattering length changes from 0 to . Using an
effective one-dimensional form of this equation, we study the phenomenon of
dynamical self-trapping of a cigar-shaped Fermi super-fluid in the entire
BEC-unitarity crossover in a double-well potential. A simple two-mode model is
constructed to provide analytical insights. We also discuss the consequence of
our study on the self-trapping of an atomic BEC in a double-well potential.Comment: 10 pages, 9 figure
Dynamical properties of dipolar Fermi gases
We investigate dynamical properties of a one-component Fermi gas with
dipole-dipole interaction between particles. Using a variational function based
on the Thomas-Fermi density distribution in phase space representation, the
total energy is described by a function of deformation parameters in both real
and momentum space. Various thermodynamic quantities of a uniform dipolar Fermi
gas are derived, and then instability of this system is discussed. For a
trapped dipolar Fermi gas, the collective oscillation frequencies are derived
with the energy-weighted sum rule method. The frequencies for the monopole and
quadrupole modes are calculated, and softening against collapse is shown as the
dipolar strength approaches the critical value. Finally, we investigate the
effects of the dipolar interaction on the expansion dynamics of the Fermi gas
and show how the dipolar effects manifest in an expanded cloud.Comment: 14 pages, 8 figures, submitted to New J. Phy
Coherent population trapping and dynamical instability in the nonlinearly coupled atom-molecule system
We study the possibility of creating a coherent population trapping (CPT)
state, involving free atomic and ground molecular condensates, during the
process of associating atomic condensate into molecular condensate. We
generalize the Bogoliubov approach to this multi-component system and study the
collective excitations of the CPT state in the homogeneous limit. We develop a
set of analytical criteria based on the relationship among collisions involving
atoms and ground molecules, which are found to strongly affect the stability
properties of the CPT state, and use it to find the stability diagram and to
systematically classify various instabilities in the long-wavelength limit.Comment: 11 pages, 8 figure
Structural phase transitions of vortex matter in an optical lattice
We consider the vortex structure of a rapidly rotating trapped atomic
Bose-Einstein condensate in the presence of a co-rotating periodic optical
lattice potential. We observe a rich variety of structural phases which reflect
the interplay of the vortex-vortex and vortex-lattice interactions. The lattice
structure is very sensitive to the ratio of vortices to pinning sites and we
observe structural phase transitions and domain formation as this ratio is
varied.Comment: 4 pages, 3 figure
On the single mode approximation in spinor-1 atomic condensate
We investigate the validity conditions of the single mode approximation (SMA)
in spinor-1 atomic condensate when effects due to residual magnetic fields are
negligible. For atomic interactions of the ferromagnetic type, the SMA is shown
to be exact, with a mode function different from what is commonly used.
However, the quantitative deviation is small under current experimental
conditions (for Rb atoms). For anti-ferromagnetic interactions, we find
that the SMA becomes invalid in general. The differences among the mean field
mode functions for the three spin components are shown to depend strongly on
the system magnetization. Our results can be important for studies of beyond
mean field quantum correlations, such as fragmentation, spin squeezing, and
multi-partite entanglement.Comment: Revised, newly found analytic proof adde
Modulational instability of spinor condensates
We demonstrate, analytically and numerically, that the ferromagnetic phase of
the spinor Bose-Einstein condenstate may experience modulational instability of
the ground state leading to a fragmentation of the spin domains. Together with
other nonlinear effects in the atomic optics of ultra-cold gases (such as
coherent photoassociation and four-wave mixing) this effect provides one more
analogy between coherent matter waves and light waves in nonlinear optics.Comment: 4 pages, 4 figures. Accepted for Phys. Rev. A Rapid Communication
Binary Bose-Einstein Condensate Mixtures in Weakly and Strongly Segregated Phases
We perform a mean-field study of the binary Bose-Einstein condensate mixtures
as a function of the mutual repulsive interaction strength. In the phase
segregated regime, we find that there are two distinct phases: 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 its 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 lower critical condensate-atom number to observe the complete
phase segregation is discussed. A comparison to recent experimental data
suggests that the weakly segregated phase has been observed.Comment: minor change
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