The Ideal Bose Gas

A. I. Bugrij, В. М. Локтев

Ideal Bose-gas with finite particle number N is investigated. It is shown that the well-known Bose–Einstein distribution of particles over their quantum states consists of two terms — Bose–Einstein term and an additional N-dependent one. The statement that the chemical potential of the ideal Bose-gas should be negative requires to be also corrected. It is obtained that the analytically calculated observables rather slowly approach the thermodynamic limit following the law N−1/3lnN.

Walter Greiner, Ludwig Neise, Horst Stöcker B

Ravinder Rupchand Puri

J.-B. Bru, Valentin Anatol'evich Zagrebnov

We show that the pressure of the Bogoliubov weakly imperfect Bose gas (WIBG) can be calculated exactly in the thermodynamic limit. We point out the sufficient and necessary conditions for it not to equate with the pressure of the ideal Bose gas (IBG). We prove that they differ only in that part of the phase diagram where the WIBG has a Bose condensate. We show that in contast to the conventional Bose condensate (e.g. in the IBG) the condensate in the WIBG is due to an effective attraction between bosons in the zero-mode.

Jérôme Estève, Jean-Baptiste Trebbia, Thorsten Schumm +3 more

We report in situ measurements of density fluctuations in a quasi-one-dimensional 87Rb Bose gas at thermal equilibrium in an elongated harmonic trap. We observe an excess of fluctuations compared to the shot-noise level expected for uncorrelated atoms. At low atomic density, the measured excess is in good agreement with the expected "bunching" for an ideal Bose gas. At high density, the measured fluctuations are strongly reduced compared to the ideal gas case. We attribute this reduction to repulsive interatomic interactions. The data are compared with a calculation for an interacting Bose gas in the quasicondensate regime.