Mean-field interaction-induced dimensional crossover from two to three dimensions in a weakly interacting Bose gas

We study an interaction-induced dimensional crossover from two to three dimensions in a weakly interacting Rb-87 Bose-Einstein condensate (BEC). A highly oblate harmonic optical dipole trap was used where we independently controlled the chemical potential and the temperature of the gas. The dimensional crossover was studied from the thermal state occupancy of atoms. In particular, the growth rate of the thermal component was measured, which contradicted the expected behavior in a fixed dimension. Crossover chemical potential and temperature were obtained at the crossover point. We further validate our observation by numerical calculations based on mean-field Hartree-Fock theory and local density approximation, which not only provided a qualitative picture of the underlying mechanism for the dimensional crossover, but also matched well with the experimentally measured crossover parameter.