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Many-Body Effects in Bose-Einstein Condensates of Dilute Atomic Gases

TitleMany-Body Effects in Bose-Einstein Condensates of Dilute Atomic Gases
Publication TypeThesis
Year of Publication1997
AuthorsEsry, BD
Academic DepartmentDepartment of Physics, University of Colorado Boulder
DegreeDoctor of Philosophy
Number of Pages199
Date Published1997-06
UniversityUniversity of Colorado
CityBoulder
Abstract

The recent experimental achievement of Bose-Einstein condensation in a dilute alkali gas has spurred a great deal of interest among physicists from many fields. Dilute atomic gas experiments are particularly attractive, compared to experiments on the closely related phenomena of superfluidity and superconductivity, because a dilute gas is a weakly interacting system which is far more amenable to theoretical description. Experimentally, dilute gas experiments are advantageous because relatively straightforward and convenient diagnostics exist, using laser excitation of atomic transitions. As a result, dilute atomic gas experiments can be more completely understood using first principles theoretical treatments

I have adapted the Hartree-Fock, random phase, and configuration interaction approximations to describe systems of interacting bosons, and have shown that such systems can be treated accurately and efficiently within a particle number conserving approximation. In fact, the resulting approximations are remarkably similar to those made in the standard Bogoliubov approach and lead to largely the same equations. A key conclusion is that a system of interacting bosons can be treated in a manner analogous to that used to describe the electronic states of atoms. The hope is that the knowledge and intuition that have been gained from the extensive study of the atomic structure problem will ultimately lead to a deeper understanding of the quantum mechanical states of interacting, trapped atoms

In the course of this work, several phenomena are studied using both the Hartree-Fock approximation and the random phase approximation. The resulting analysis of the stability criteria for single and double condensates improves on results available in the literature in both cases. The double condensate ground state is explored for various hyperfine and isotopic combinations of rubidium in fully three-dimensional con¯gyrations for realistic numbers of atoms. Random phase approximation excitation spectra are also calculated for both single and double iv condensates. Many of these predictions have not yet been tested experimentally, nor is there any other theoretical treatment with which comparisons can be made. A systematic study of spatial symmetry breaking at the Hartree-Fock level of approximation for the ground state of double condensates is also presented.