Semi classical description of a finite temperature Bose Einstein condensate

The semi-classical theory of a finite temperature Bose condensed gas is presented, based on the Gross-Pitaevskii equation. The theory leads to a straight forward numerical technique used to generate self-consistent thermally-excited states of a dilute boson gas, results of which are presented. The numerical technique is generalised to multi-component spinor fields, with results presented for the self-consistent thermally-excited states of a two-component field. The process of evaporative cooling is modeled by following the time evolution of the system using the same equation. It is shown that the subsequent rethermalisation of the thermally-excited state produces a cooler, more coherent condensate. Further results presented show that trapping vortex states with the ground state may be possible. The process of sympathetic cooling is modeled in a two-component spinor field using a generalisation of the evaporative cooling model. Results presented show that the subsequent rethermalisation and cross-thermalisation of the fields produces a cooler spinor condensate. Results of the numerical calculation of the energy spectrum of a self-consistent thermally-excited state are presented. It is shown that the Gross-Pitaevskii equation leads to the reproduction of the Kohn modes to an accuracy of 0.08%, a direct result of treating all the excited modes consistently. The temperature of the self-consistent thermally-excited state is calculated in the non-interacting limit. It is shown that the maximum condensate population occurs for a normalised temperature of T/T"0c #approx# 0.4. Finally, a direct characterisation of the temperature of the Bose-condensed gas with respect to the position of the 'r.f. scalpel' during the evaporative cooling process is presented. (author)Available from British Library Document Supply Centre- DSC:DXN057397 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo