5,238 research outputs found
BCS Theory for Trapped Ultracold Fermions
We develop an extension of the well-known BCS-theory to systems with trapped
fermions. The theory fully includes the quantized energy levels in the trap.
The key ingredient is to model the attractive interaction between two atoms by
a pseudo-potential which leads to a well defined scattering problem and
consequently a BCS-theory free of divergences. We present numerical results for
the BCS critical temperature and the temperature dependence of the gap. They
are used as a test of existing semi-classical approximations.Comment: 4 pages, 3 figures, submitted to PR
Characterisation of the dynamical quantum state of a zero temperature Bose-Einstein condensate
We describe the quantum state of a Bose-Einstein condensate at zero
temperature. By evaluating the Q-function we show that the ground state of
Bose-Einstein condensate under the Hartree approximation is squeezed. We find
that multimode Schroedinger cat states are generated as the condensate evolves
in a ballistic expansion.Comment: 13 pages, 6 figure
Classical field techniques for condensates in one-dimensional rings at finite temperatures
For a condensate in a one-dimensional ring geometry, we compare the
thermodynamic properties of three conceptually different classical field
techniques: stochastic dynamics, microcanonical molecular dynamics, and the
classical field method. Starting from non-equilibrium initial conditions, all
three methods approach steady states whose distribution and correlation
functions are in excellent agreement with an exact evaluation of the partition
function in the high-temperature limit. Our study helps to establish these
various classical field techniques as powerful non-perturbative tools for
systems at finite temperatures.Comment: 7 pages, 7 figures; minor changes, one reference adde
Creation of macroscopic superposition states from arrays of Bose-Einstein condensates
We consider how macroscopic quantum superpositions may be created from arrays
of Bose-Einstein condensates. We study a system of three condensates in Fock
states, all with the same number of atoms and show that this has the form of a
highly entangled superposition of different quasi-momenta. We then show how, by
partially releasing these condensates and detecting an interference pattern
where they overlap, it is possible to create a macroscopic superposition of
different relative phases for the remaining portions of the condensates. We
discuss methods for confirming these superpositions.Comment: 7 pages, 5 figure
Ultracold Bosonic Atoms in Disordered Optical Superlattices
The influence of disorder on ultracold atomic Bose gases in quasiperiodic
optical lattices is discussed in the framework of the one-dimensional
Bose-Hubbard model. It is shown that simple periodic modulations of the well
depths generate a rich phase diagram consisting of superfluid, Mott insulator,
Bose-glass and Anderson localized phases. The detailed evolution of mean
occupation numbers and number fluctuations as function of modulation amplitude
and interaction strength is discussed. Finally, the signatures of the different
phases, especially of the Bose-glass phase, in matter-wave interference
experiments are investigated.Comment: 4 pages, 4 figures, using REVTEX
Influence of spontaneous emission on laser-induced autoionization
A master equation that describes the effect of spontaneous emission on laser-induced autoionization is formulated and its solution is obtained for arbitrary laser strengths. The radiative decay is shown to affect drastically the nature of spectra near confluence. Analytic expressions for widths and positions are given to demonstrate the new features of spectra
Photoemission spectra in intense laser field induced autoionization
Photoemission spectra from autoionizing states in the presence of a strong laser field are calculated. Such spectra have very sharp features near "confluence" (at the Fano minimum) and are very similar, in structure, to photoelectron spectra. The total intensity, as a function of laser intensity or detuning, has a peak near confluence, which can be used, among other things, for the accurate determination of Fano asymmetry parameter q
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