11,695 research outputs found
Motion of a condensate in a shaken and vibrating harmonic trap
The dynamics of a Bose-Einstein condensate (BEC) in a time-dependent harmonic
trapping potential is determined for arbitrary variations of the position of
the center of the trap and its frequencies. The dynamics of the BEC wavepacket
is soliton-like. The motion of the center of the wavepacket, and the spatially
and temporally dependent phase (which affects the coherence properties of the
BEC) multiplying the soliton-like part of the wavepacket, are analytically
determined.Comment: Accepted for publication in J. Phys. B: At Mol Opt Phy
Expansion of an interacting Fermi gas
We study the expansion of a dilute ultracold sample of fermions initially
trapped in a anisotropic harmonic trap. The expansion of the cloud provides
valuable information about the state of the system and the role of
interactions. In particular the time evolution of the deformation of the
expanding cloud behaves quite differently depending on whether the system is in
the normal or in the superfluid phase. For the superfluid phase, we predict an
inversion of the deformation of the sample, similarly to what happens with
Bose-Einstein condensates. Viceversa, in the normal phase, the inversion of the
aspect ratio is never achieved, if the mean field interaction is attractive and
collisions are negligible.Comment: 4 pages, 3 figures, final versio
Critical Dynamics of a Two-dimensional Superfluid near a Non-Thermal Fixed Point
Critical dynamics of an ultracold Bose gas far from equilibrium is studied in
two spatial dimensions. Superfluid turbulence is created by quenching the
equilibrium state close to zero temperature. Instead of immediately
re-thermalizing, the system approaches a meta-stable transient state,
characterized as a non-thermal fixed point. A focus is set on the vortex
density and vortex-antivortex correlations which characterize the evolution
towards the non-thermal fixed point and the departure to final
(quasi-)condensation. Two distinct power-law regimes in the vortex-density
decay are found and discussed in terms of a vortex binding-unbinding transition
and a kinetic description of vortex scattering. A possible relation to decaying
turbulence in classical fluids is pointed out. By comparing the results to
equilibrium studies of a two-dimensional Bose gas, an intuitive understanding
of the location of the non-thermal fixed point in a reduced phase space is
developed.Comment: 11 pages, 13 figures; PRA versio
Superconductivity from repulsive interactions in the two dimensional electron gas
We present a well-controlled perturbative renormalization group (RG)
treatment of superconductivity from short-ranged repulsive interactions in a
variety of model two dimensional electronic systems. Our analysis applies in
the limit where the repulsive interactions between the electrons are small
compared to their kinetic energy.Comment: 10 pages 3 figure
Bound states of three and four resonantly interacting particles
We present an exact diagrammatic approach for the problem of dimer-dimer
scattering in 3D for dimers being a resonant bound state of two fermions in a
spin-singlet state, with corresponding scattering length . Applying this
approach to the calculation of the dimer-dimer scattering length , we
recover exactly the already known result . We use the developed
approach to obtain new results in 2D for fermions as well as for bosons.
Namely, we calculate bound state energies for three and four
resonantly interacting bosons in 2D. For the case of resonant interaction
between fermions and bosons we calculate exactly bound state energies of the
following complexes: two bosons plus one fermion , two bosons plus two
fermions , and three bosons plus one fermion
.Comment: 10 pages, 9 figure
- …