10 research outputs found
Collective Motion of Polarized Dipolar Fermi Gases in the Hydrodynamic Regime
Recently, a seminal STIRAP experiment allowed the creation of 40K-87Rb
molecules in the rovibrational ground state [K.-K. Ni et al., Science 322, 231
(2008)]. In order to describe such a polarized dipolar Fermi gas in the
hydrodynamic regime, we work out a variational time-dependent Hartree-Fock
approach. With this we calculate dynamical properties of such a system as, for
instance, the frequencies of the low-lying excitations and the time-of-flight
expansion. We find that the dipole-dipole interaction induces anisotropic
breathing oscillations in momentum space. In addition, after release from the
trap, the momentum distribution becomes asymptotically isotropic, while the
particle density becomes anisotropic
Quantum Fluctuations in Dipolar Bose Gases
We investigate the influence of quantum fluctuations upon dipolar Bose gases
by means of the Bogoliubov-de Gennes theory. Thereby, we make use of the local
density approximation to evaluate the dipolar exchange interaction between the
condensate and the excited particles. This allows to obtain the Bogoliubov
spectrum analytically in the limit of large particle numbers. After discussing
the condensate depletion and the ground-state energy correction, we derive
quantum corrected equations of motion for harmonically trapped dipolar Bose
gases by using superfluid hydrodynamics. These equations are subsequently
applied to analyze the equilibrium configuration, the low-lying oscillation
frequencies, and the time-of-flight dynamics. We find that both atomic magnetic
and molecular electric dipolar systems offer promising scenarios for detecting
beyond mean-field effects.Comment: Published in PR
Rotating Fermi gases in an anharmonic trap
Motivated by recent experiments on rotating Bose-Einstein condensates, we
investigate a rotating, polarized Fermi gas trapped in an anharmonic potential.
We apply a semiclassical expansion of the density of states in order to
determine how the thermodynamic properties depend on the rotation frequency.
The accuracy of the semiclassical approximation is tested and shown to be
sufficient for describing typical experiments. At zero temperature, rotating
the gas above a given frequency leads to a `donut'-shaped
cloud which is analogous to the hole found in two-dimensional Bose-Einstein
condensates. The free expansion of the gas after suddenly turning off the trap
is considered and characterized by the time and rotation frequency dependence
of the aspect ratio. Temperature effects are also taken into account and both
low- and high-temperature expansions are presented for the relevant
thermodynamical quantities. In the high-temperature regime a virial theorem
approach is used to study the delicate interplay between rotation and
anharmonicity
Bound vortex states and exotic lattices in multi-component Bose-Einstein condensates: The role of vortex-vortex interaction
We numerically study the vortex-vortex interaction in multi-component
homogeneous Bose-Einstein condensates within the realm of the Gross-Pitaevskii
theory. We provide strong evidences that pairwise vortex interaction captures
the underlying mechanisms which determine the geometric configuration of the
vortices, such as different lattices in many-vortex states, as well as the
bound vortex states with two (dimer) or three (trimer) vortices. Specifically,
we discuss and apply our theoretical approach to investigate intra- and
inter-component vortex-vortex interactions in two- and three-component
Bose-Einstein condensates, thereby shedding light on the formation of the
exotic vortex configurations. These results correlate with current experimental
efforts in multi-component Bose-Einstein condensates, and the understanding of
the role of vortex interactions in multiband superconductors.Comment: Published in PR