701 research outputs found
A superfluid gyroscope with cold atomic gases
A trapped Bose-Einstein condensed atomic gas containing a quantized vortex is
predicted to exhibit precession after a sudden rotation of the confining
potential.
The equations describing the motion of the condensate are derived and the
effects of superfluidity explicitly pointed out. The dependence of the
precession frequency on the relevant parameters of the problem is discussed.
The proposed gyroscope is well suited to explore rotational effects at the
level of single quanta of circulation.Comment: 1 eps figur
Molecular signatures in the structure factor of an interacting Fermi gas
The static and dynamic structure factors of an interacting Fermi gas along
the BCS-BEC crossover are calculated at momentum transfer higher
than the Fermi momentum. The spin structure factor is found to be very
sensitive to the correlations associated with the formation of molecules. On
the BEC side of the crossover, even close to unitarity, clear evidence is found
for a molecular excitation at , where is the atomic mass.
Both quantum Monte Carlo and dynamic mean-field results are presented.Comment: 4 pages, 4 figure
Dipolar Drag in Bilayer Harmonically Trapped Gases
We consider two separated pancake-shaped trapped gases interacting with a
dipolar (either magnetic or electric) force. We study how the center of mass
motion propagates from one cloud to the other as a consequence of the
long-range nature of the interaction. The corresponding dynamics is fixed by
the frequency difference between the in-phase and the out-of-phase center of
mass modes of the two clouds, whose dependence on the dipolar interaction
strength and the cloud separation is explicitly investigated. We discuss Fermi
gases in the degenerate as well as in the classical limit and comment on the
case of Bose-Einsten condensed gases.Comment: Submitted to EPJD, EuroQUAM special issue "Cold Quantum Matter -
Achievements and Prospects
Density and spin response function of a normal Fermi gas at unitarity
Using Landau theory of Fermi liquids we calculate the dynamic response of
both a polarized and unpolarized normal Fermi gas at zero temperature in the
strongly interacting regime of large scattering length. We show that at small
excitation energies the {\it in phase} (density) response is enhanced with
respect to the ideal gas prediction due to the increased compressibility.
Viceversa, the {\it out of phase} (spin) response is quenched as a consequence
of the tendency of the system to pair opposite spins. The long wavelength
behavior of the static structure factor is explicitly calculated. The results
are compared with the predictions in the collisional and superfluid regimes.
The emergence of a spin zero sound solution in the unpolarized normal phase is
explicitly discussed.Comment: 4 pages, 2 figure
First and second sound in cylindrically trapped gases
We investigate the propagation of density and temperature waves in a
cylindrically trapped gas with radial harmonic confinement. Starting from
two-fluid hydrodynamic theory we derive effective 1D equations for the chemical
potential and the temperature which explicitly account for the effects of
viscosity and thermal conductivity. Differently from quantum fluids confined by
rigid walls, the harmonic confinement allows for the propagation of both first
and second sound in the long wave length limit. We provide quantitative
predictions for the two sound velocities of a superfluid Fermi gas at
unitarity. For shorter wave-lengths we discover a new surprising class of
excitations continuously spread over a finite interval of frequencies. This
results in a non-dissipative damping in the response function which is
analytically calculated in the limiting case of a classical ideal gas.Comment: 4 pages, 2 figures. Published version in Phys. Rev. Let
Dynamical instability and dispersion management of an attractive condensate in an optical lattice
We investigate the stability of an attractive Bose-Einstein condensate in a
moving 1D optical lattice in the presence of transverse confinement. By means
of a Bogoliubov linear stability analysis we find that the system is
dynamically unstable for low quasimomenta and becomes stable near the band
edge, in a specular fashion with respect to the repulsive case. For low
interactions the instability occurs via long wavelength excitations that are
not sufficient for spoiling the condensate coherence, producing instead an
oscillating density pattern both in real and momentum space. This behaviour is
illustrated by simulations for the expansion of the condensate in a moving
lattice.Comment: 5 pages, 4 figure
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