1,512 research outputs found
Anderson localization of pairs in bichromatic optical lattices
We investigate the formation of bound states made of two interacting atoms
moving in a one dimensional (1D) quasi-periodic optical lattice. We derive the
quantum phase diagram for Anderson localization of both attractively and
repulsively bound pairs. We calculate the pair binding energy and show
analytically that its behavior as a function of the interaction strength
depends crucially on the nature -extended, multi-fractal, localized- of the
single-particle atomic states. Experimental implications of our results are
discussed.Comment: final revised version with more explanations, 4 pages, 3 figure
Equilibrium and dynamics of a trapped superfluid Fermi gas with unequal masses
Interacting Fermi gases with equal populations but unequal masses are
investigated at zero temperature using local density approximation and the
hydrodynamic theory of superfluids in the presence of harmonic trapping.
We derive the conditions of energetic stability of the superfluid
configuration with respect to phase separation and the frequencies of the
collective oscillations in terms of the mass ratio and the trapping frequencies
of the two components. We discuss the behavior of the gas after the trapping
potential of a single component is switched off and show that, near a Feshbach
resonance, the released component can still remain trapped due to many-body
interaction effects. Explicit predictions are presented for a mixture of Li
and K with resonant interaction.Comment: 4 pages, 2 figure
Umklapp collisions and center of mass oscillation of a trapped Fermi gas
Starting from the the Boltzmann equation, we study the center of mass
oscillation of a harmonically trapped normal Fermi gas in the presence of a
one-dimensional periodic potential. We show that for values of the the Fermi
energy above the first Bloch band the center of mass motion is strongly damped
in the collisional regime due to umklapp processes. This should be contrasted
with the behaviour of a superfluid where one instead expects the occurrence of
persistent Josephson-like oscillations.Comment: 11 pages, 3 figures, corrected typo
Quantum Monte Carlo simulations of two-dimensional repulsive Fermi gases with population imbalance
The ground-state properties of two-component repulsive Fermi gases in two
dimensions are investigated by means of fixed-node diffusion Monte Carlo
simulations. The energy per particle is determined as a function of the
intercomponent interaction strength and of the population imbalance. The regime
of universality in terms of the s-wave scattering length is identified by
comparing results for hard-disk and for soft-disk potentials. In the large
imbalance regime, the equation of state turns out to be well described by a
Landau-Pomeranchuk functional for two-dimensional polarons. To fully
characterize this expansion, we determine the polarons' effective mass and
their coupling parameter, complementing previous studies on their chemical
potential. Furthermore, we extract the magnetic susceptibility from
low-imbalance data, finding only small deviations from the mean-field
prediction. While the mean-field theory predicts a direct transition from a
paramagnetic to a fully ferromagnetic phase, our diffusion Monte Carlo results
suggest that the partially ferromagnetic phase is stable in a narrow interval
of the interaction parameter. This finding calls for further analyses on the
effects due to the fixed-node constraint.Comment: 10 pages, 5 figure
Sound propagation and oscillations of a superfluid Fermi gas in the presence of a 1D optical lattice
We develop the hydrodynamic theory of Fermi superfluids in the presence of a
periodic potential. The relevant parameters governing the propagation of sound
(compressibility and effective mass) are calculated in the weakly interacting
BCS limit. The conditions of stability of the superfluid motion with respect to
creation of elementary excitations are discussed.
We also evaluate the frequency of the center of mass oscillation when the
superfluid gas is additionally confined by a harmonic trap.Comment: Version accepted in Phys. Rev. A. It contains a discussion on the
dynamical instability of Fermi superfluids in optical lattice
In-Plane Conductivity Anisotropy in Underdoped Cuprates in the Spin-Charge Gauge Approach
Applying the recently developed spin-charge gauge theory for the pseudogap
phase in cuprates, we propose a self-consistent explanation of several peculiar
features of the far-infrared in-plane AC conductivity, including a broad peak
as a function of frequency and significant anisotropy at low temperatures,
along with a similar temperature-dependent in-plane anisotropy of DC
conductivity in lightly doped cuprates. The anisotropy of the metal-insulator
crossover scale is considered to be responsible for these phenomena. The
obtained results are in good agreement with experiments. An explicit proposal
is made to further check the theory.Comment: 5 pages, 3 figures, to appear in Phys. Rev.
Landau-Zener sweeps and sudden quenches in coupled Bose-Hubbard chains
We simulate numerically the dynamics of strongly correlated bosons in a
two-leg ladder subject to a time-dependent energy bias between the two chains.
When all atoms are initially in the leg with higher energy, we find a drastic
reduction of the inter-chain particle transfer for slow linear sweeps, in
quantitative agreement with recent experiments. This effect is preceded by a
rapid broadening of the quasi-momentum distribution of atoms, signaling the
presence of a bath of low-energy excitations in the chains. We further
investigate the scenario of quantum quenches to fixed values of the energy
bias. We find that for large enough density the momentum distribution relaxes
to that of an equilibrium thermal state with the same energy.Comment: 6 pages, 4 figure
Long-time behavior of the momentum distribution during the sudden expansion of a spin-imbalanced Fermi gas in one dimension
We study the sudden expansion of spin-imbalanced ultracold lattice fermions
with attractive interactions in one dimension after turning off the
longitudinal confining potential. We show that the momentum distribution
functions of majority and minority fermions approach stationary values quickly
due to a quantum distillation mechanism that results in a spatial separation of
pairs and majority fermions. As a consequence, Fulde-Ferrell-Larkin-Ovchinnikov
(FFLO) correlations are lost during the expansion. Furthermore, we argue that
the shape of the stationary momentum distribution functions can be understood
by relating them to the integrals of motion in this integrable quantum system.
We discuss our results in the context of proposals to observe FFLO
correlations, related to recent experiments by Liao et al., Nature 467, 567
(2010).Comment: 8 pages including supplementary material, 9 eps figures, revised
version as published, some text moved to the supplemental materia
Superfluid Fermi gas in a 1D optical lattice
We calculate the superfluid transition temperature for a two-component 3D
Fermi gas in a 1D tight optical lattice and discuss a dimensional crossover
from the 3D to quasi-2D regime. For the geometry of finite size discs in the 1D
lattice, we find that even for a large number of atoms per disc, the critical
effective tunneling rate for a quantum transition to the Mott insulator state
can be large compared to the loss rate caused by three-body recombination. This
allows the observation of the Mott transition, in contrast to the case of
Bose-condensed gases in the same geometry.Comment: 4 pages, 1 figur
A wearable multimodal interface for exploring urban points of interest
Locating points of interest (POIs) in cities is typically facilitated by visual aids such as paper maps, brochures, and mobile applications. However, these techniques require visual attention, which ideally should be on the surroundings. Non-visual techniques for navigating towards specific POIs typically lack support for free exploration of the city or more detailed guidance. To overcome these issues, we propose a multimodal, wearable system for alerting the user of nearby recommended POIs. The system, built around a tactile glove, provides audio-tactile cues when a new POI is in the vicinity, and more detailed information and guidance if the user expresses interest in this POI. We evaluated the system in a field study, comparing it to a visual baseline application. The encouraging results show that the glovebased system helps keep the attention on the surroundings and that its performance is on the same level as that of the baseline
- …