29 research outputs found
Directed transport and Floquet analysis for a periodically kicked wavepacket at a quantum resonance
The dynamics of a kicked quantum mechanical wavepacket at a quantum resonance
is studied in the framework of Floquet analysis. It is seen how a directed
current can be created out of a homogeneous initial state at certain resonances
in an asymmetric potential. The almost periodic parameter dependence of the
current is found to be connected with level crossings in the Floquet spectrum.Comment: 8 pages, 4 figures, submitted to Phys. Rev.
Ratchet effect for cold atoms in an optical lattice
The realization of a directed current for a quantum particle in a flashing
asymmetric potential is studied. It is found that a positive current, i.e. in
the direction expected for a conventional diffusive ratchet, can be attained at
short times in the limit where the potential is weak and quantum diffusion
dominates, while current reversal is obtained for stronger potentials. A single
parameter, the ratio between the kicking frequency and the optical lattice
potential strength, determines both the degree to which quantum effects
dominate, and the possibility of obtaining a ratchet current. The effect should
be readily observable in experiments.Comment: 4 pages, 3 figure
Construction of a giant vortex state in a trapped Fermi system
A superfluid atomic Fermi system may support a giant vortex if the trapping
potential is anharmonic. In such a potential, the single-particle spectrum has
a positive curvature as a function of angular momentum. A tractable model is
put up in which the lowest and next lowest Landau levels are occupied.
Different parameter regimes are identified and characterized. Due to the
dependence of the interaction on angular momentum quantum number, the Cooper
pairing is at its strongest not only close to the Fermi level, but also close
to the energy minimum. It is shown that the gas is superfluid in the interior
of the toroidal density distribution and normal in the outer regions.
Furthermore, the pairing may give rise to a localized density depression in
configuration space.Comment: 12 pages, 14 figure file