1,924 research outputs found
Pairing in a three component Fermi gas
We consider pairing in a three-component gas of degenerate fermions. In
particular, we solve the finite temperature mean-field theory of an interacting
gas for a system where both interaction strengths and fermion masses can be
unequal. At zero temperature we find a a possibility of a quantum phase
transition between states associated with pairing between different pairs of
fermions. On the other hand, finite temperature behavior of the three-component
system reveals some qualitative differences from the two-component gas: for a
range of parameters it is possible to have two different critical temperatures.
The lower one corresponds to a transition between different pairing channels,
while the higher one corresponds to the usual superfluid-normal transition. We
discuss how these phase transitions could be observed in ultracold gases of
fermionic atoms.Comment: 10 pages, 3 figure
Vortex-line solitons in a periodically modulated Bose gas
We study the nonlinear excitations of a vortex-line in a Bose-Einstein
condensate trapped in a one-dimensional optical lattice. We find that the
classical Euler dynamics of the vortex results in a description of the vortex
line in terms of a (discrete) one-dimensional Gross-Pitaevskii equation, which
allows for both bright and gray soliton solutions. We discuss these solutions
in detail and predict that it is possible to create vortex-line solitons with
current experimental capabilities.Comment: minor changes, updated/corrected references, 4 pages, 3 figure
Noise correlations of the ultra-cold Fermi gas in an optical lattice
In this paper we study the density noise correlations of the two component
Fermi gas in optical lattices. Three different type of phases, the BCS-state
(Bardeen, Cooper, and Schieffer), the FFLO-state (Fulde, Ferrel, Larkin, and
Ovchinnikov), and BP (breach pair) state, are considered. We show how these
states differ in their noise correlations. The noise correlations are
calculated not only at zero temperature, but also at non-zero temperatures
paying particular attention to how much the finite temperature effects might
complicate the detection of different phases. Since one-dimensional systems
have been shown to be very promising candidates to observe FFLO states, we
apply our results also to the computation of correlation signals in a
one-dimensional lattice. We find that the density noise correlations reveal
important information about the structure of the underlying order parameter as
well as about the quasiparticle dispersions.Comment: 25 pages, 11 figures. Some figures are updated and text has been
modifie
Finite temperature phase diagram of a polarized Fermi gas in an optical lattice
We present phase diagrams for a polarized Fermi gas in an optical lattice as
a function of temperature, polarization, and lattice filling factor. We
consider the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO), Sarma or breached pair
(BP), and BCS phases, and the normal state and phase separation. We show that
the FFLO phase appears in a considerable portion of the phase diagram. The
diagrams have two critical points of different nature. We show how various
phases leave clear signatures to momentum distributions of the atoms which can
be observed after time of flight expansion.Comment: Journal versio
Quantum fluctuations of a vortex in an optical lattice
Using a variational ansatz for the wave function of the Bose-Einstein
condensate, we develop a quantum theory of vortices and quadrupole modes in a
one-dimensional optical lattice. We study the coupling between the quadrupole
modes and Kelvin modes, which turns out to be formally analogous to the theory
of parametric processes in quantum optics. This leads to the possibility of
squeezing vortices. We solve the quantum multimode problem for the Kelvin modes
and quadrupole modes numerically and find properties that cannot be explained
with a simple linear-response theory.Comment: final version, minor change
Spontaneous squeezing of a vortex in an optical lattice
We study the equilibrium states of a vortex in a Bose-Einstein condensate in
a one-dimensional optical lattice. We find that quantum effects can be
important and that it is even possible for the vortex to be strongly squeezed,
which reflects itself in a different quantum mechanical uncertainty of the
vortex position in two orthogonal directions. The latter is observable by
measuring the atomic density after an expansion of the Bose-Einstein condensate
in the lattice.Comment: 8 pages, 3 figures, more details added, some new citation
Interband physics in an ultra-cold Fermi gas in an optical lattice
We study a gas of strongly polarized cold fermions in an optical lattice when
the excited p-bands are populated. We derive the relevant Hamiltonian and
discuss the expected phase diagram for both repulsive and attractive
interactions. In the parameter regime covered here, checkerboard
anti-ferromagnetic ordering is found to be possible for repulsive interactions
while for attractive interactions, transitions between different types of
paired phases are predicted.Comment: 5 pages, 2 figure
Quantum theory of a vortex line in an optical lattice
We investigate the quantum theory of a vortex line in a stack of
weakly-coupled two-dimensional Bose-Einstein condensates, that is created by a
one-dimensional optical lattice. We derive the dispersion relation of the
Kelvin modes of the vortex line and also study the coupling between the Kelvin
modes and the quadrupole modes. We solve the coupled dynamics of the vortex
line and the quadrupole modes, both classically as well as quantum
mechanically. The quantum mechanical solution reveals the possibility of
generating nonequilibrium squeezed vortex states by strongly driving the
quadrupole modes.Comment: Minor changes in response to a referee repor
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