Growth dynamics of a Bose-Einstein condensate in a dimple trap without cooling

Michael C. Garrett, Adrian Ratnapala, Eikbert D. van Ooijen, Christopher J. Vale, Kristian Weegink, Sebastian K. Schnelle, Otto Vainio, Norman R. Heckenberg, Halina Rubinsztein-Dunlop and Matthew J. Davis

We study the formation of a Bose-Einstein condensate in a cigar-shaped three-dimensional harmonic trap, induced by the controlled addition of an attractive “dimple” potential along the weak axis. In this manner we are able to induce condensation without cooling due to a localized increase in the phase-space density. We perform a quantitative analysis of the thermodynamic transformation in both the sudden and adiabatic regimes for a range of dimple widths and depths. We find good agreement with equilibrium calculations based on self-consistent semiclassical Hartree-Fock theory describing the condensate and thermal cloud. We observe that there is an optimal dimple depth that results in a maximum in the condensate fraction. We also study the nonequilibrium dynamics of condensate formation in the sudden turn-on regime, finding good agreement for the observed time dependence of the condensate fraction with calculations based on quantum kinetic theory.