Physics – Condensed Matter – Statistical Mechanics
Scientific paper
2002-12-20
Phys. Rev. A 67, 053615 (2003)
Physics
Condensed Matter
Statistical Mechanics
32 pages, 2 figures; typos corrected in revised version
Scientific paper
10.1103/PhysRevA.67.053615
We present an extension of the well-known Bogoliubov theory to treat low dimensional degenerate Bose gases in the limit of weak interactions and low density fluctuations. We use a density-phase representation and show that a precise definition of the phase operator requires a space discretisation in cells of size $l$. We perform a systematic expansion of the Hamiltonian in terms of two small parameters, the relative density fluctuations inside a cell and the phase change over a cell. The resulting macroscopic observables can be computed in one, two and three dimensions with no ultraviolet or infrared divergence. Furthermore this approach exactly matches Bogoliubov's approach when there is a true condensate. We give the resulting expressions for the equation of state of the gas, the ground state energy, the first order and second order correlations functions of the field. Explicit calculations are done for homogeneous systems.
Castin Yvan
Mora Christophe
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