Dimensional and temperature crossover in trapped Bose gases

A detailed universal picture of the coherence properties of a Bose gas was obtained as a function of the dimensionality, the temperature, and the interaction strength. Focus was on the crossover from quasicondensation to true Bose-Einstein condensation. In a finite homogeneous system at zero temperature, the long-range coherence is lost when the dimension of the system is reduced to one. This dimensional reduction leads to the appearance of a quasicondensate, whose coherence extends over a range that is much larger than the coherence length but much smaller than the size of the system. Similar results were obtained when the effects of temperature and the strength of the mean-field interaction were investigated.