Optimized production of large Bose-Einstein condensates

We describe several routes to quantum degenerate gases based on simple schemes to efficiently load atoms into and evaporate them from a “dimple” crossed dipolar trap. The dimple is loaded nonadiabatically by collisions between atoms which are trapped in a reservoir which can be provided either by a dark spontaneous-force magneto-optical trap (MOT), the (aberrated) laser beam itself, or by a quadrupolar or quadratic magnetic trap. Optimal loading parameters for the dimple, relatively high temperature, and tight optical trap are derived from thermodynamic equations including possible inelastic and Majorana losses. Evaporative cooling is described by a set of simple equations, taking into account gravity, the possible occurrence of the hydrodynamical regime, Feshbach resonances, and three body recombination. The solution implies that to have efficient evaporation the elastic collisional rate (in ${\mathrm{s}}^{-1}$) must be on the order of the trap frequency and lower than 100 times the temperature in microkelvins. Following this approach Bose-Einstein condensates with more than ${10}^7$ atoms should be obtained in much less than $1\mathrm{s}$ starting from an ordinary MOT setup.