Atomic, Molecular, and Optical Physics Seminar

Stability of Bose and Fermi Gases with Isotropic and Anisotropic Interactions

Professor Doerte Blume
Department of Physics and Astronomy
Washington State University

The behaviors of weakly interacting isotropic Bose gases have been successfully modeled within a mean-field framework. To this end, one replaces the true atom-atom potential by a contact interaction, whose strength is given by the s-wave scattering length, and solves the resulting many-body Schroedinger equation at the Hartree level. The resulting non-linear single-particle Schroedinger equation, also referred to as Gross-Pitaevskii equation, predicts many behaviors of inhomogeneous Bose gases accurately, including the onset of instability for Bose systems with negative two-body s-wave scattering length for a critical number of particles. This talk discusses the validity regime of mean-field treatments for anisotropic Bose gases and Fermi gases, and investigates the stability of these systems within the mean-field framework and within alternative microscopic frameworks.

Degenerate atomic Bose gases with long-range anisotropic dipolar interactions have recently been condensed experimentally. In addition to the s-wave scattering length, the behaviors of these systems depend in general on the strength of the magnetic dipole moment or, in the case of polar molecules, on the strength of the electric dipole moment. For small dipole strengths, a mean-field framework that accounts for the anisotropic interactions reproduces the results obtained using an essentially exact many-body Monte Carlo framework. For larger dipole strengths, however, the mean-field framework needs to be modified. Unlike Bose gases, two-component Fermi gases with negative interspecies s-wave scattering length are stable even when the magnitude of the s-wave scattering length becomes infinitely large. This stability is at first sight somewhat counterintuitive but can, as is now well understood, be attributed to the Fermi pressure or Pauli exclusion principle. This talk investigates how the behaviors of two-component s-wave interacting Fermi gases change when a third or fourth component are added.

Monday, December 3, 2007
4:00 PM
Gant Science Complex
Physics Department
Room P121

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