284 research outputs found
Collective modes and the speed of sound in the Fulde-Ferrell-Larkin-Ovchinnikov state
We consider the density response of a spin-imbalanced ultracold Fermi gas in
an optical lattice in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. We
calculate the collective mode spectrum of the system in the generalised random
phase approximation and find that though the collective modes are damped even
at zero tempererature, the damping is weak enough to have well-defined
collective modes. We calculate the speed of sound in the gas and show that it
is anisotropic due to the anisotropy of the FFLO pairing, which implies an
experimental signature for the FFLO state.Comment: 13 pages, 9 figures (revised version
Quasi two-dimensional superfluid Fermi gases
We study a quasi two-dimensional superfluid Fermi gas where the confinement
in the third direction is due to a strong harmonic trapping. We investigate the
behavior of such a system when the chemical potential is varied and find strong
modifications of the superfluid properties due to the discrete harmonic
oscillator states. We show that such quasi two-dimensional behavior can be
created and observed with current experimental capabilities.Comment: In response to referee comments, minor changes from the earlier
versio
Localization and diffusion in Ising-type quantum networks
We investigate the effect of phase randomness in Ising-type quantum networks.
These networks model a large class of physical systems. They describe micro-
and nanostructures or arrays of optical elements such as beam splitters
(interferometers) or parameteric amplifiers. Most of these stuctures are
promising candidates for quantum information processing networks. We
demonstrate that such systems exhibit two very distinct types of behaviour. For
certain network configurations (parameters), they show quantum localization
similar to Anderson localization whereas classical stochastic behaviour is
observed in other cases. We relate these findings to the standard theory of
quantum localization.Comment: 12 page
Density response of a trapped Fermi gas: a crossover from the pair vibration mode to the Goldstone mode
We consider the density response of a trapped two-component Fermi gas.
Combining the Bogoliubov-deGennes method with the random phase approximation
allows the study of both collective and single particle excitations.
Calculating the density response across a wide range of interactions, we
observe a crossover from a weakly interacting pair vibration mode to a strongly
interacting Goldstone mode. The crossover is associated with a depressed
collective mode frequency and an increased damping rate, in agreement with
density response experiments performed in strongly interacting atomic gases.Comment: 14 pages, 8 figure
Impurity and soliton dynamics in a Fermi gas with nearest-neighbor interactions
We study spinless fermions with repulsive nearest-neighbor interactions
perturbed by an impurity particle or a local potential quench. Using the
numerical time-evolving block decimation method and a simplified analytic
model, we show that the pertubations create a soliton-antisoliton pair. If
solitons are already present in the bath, the two excitations have a
drastically different dynamics: The antisoliton does not annihilate with the
solitons and is therefore confined close to its origin while the soliton
excitation propagates. We discuss the consequences for experiments with
ultracold gases.Comment: 12 pages, 16 figure
Fast trimers in one-dimensional extended Fermi-Hubbard model
We consider a one-dimensional two component extended Fermi-Hubbard model with
nearest neighbor interactions and mass imbalance between the two species. We
study the stability of trimers, various observables for detecting them, and
expansion dynamics. We generalize the definition of the trimer gap to include
the formation of different types of clusters originating from nearest neighbor
interactions. Expansion dynamics reveal rapidly propagating trimers, with
speeds exceeding doublon propagation in strongly interacting regime. We present
a simple model for understanding this unique feature of the movement of the
trimers, and we discuss the potential for experimental realization.Comment: 10 pages, 10 figure
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