High phase space density loading of a falling magnetic trap

TL;DR

This paper demonstrates a novel high phase space density loading method for ultra-cold Rubidium atoms into a falling magnetic trap, significantly improving efficiency by dissipating gravitational energy and enabling rapid evaporation.

Contribution

The authors introduce a high phase space loading scheme using a falling magnetic trap with unequal coil currents, achieving a 20-fold density increase over static traps.

Findings

20-fold increase in phase space density

Efficient sub-second thermalization enabling fast evaporation

Effective dissipation of gravitational energy during loading

Abstract

Loading an ultra-cold ensemble into a static magnetic trap involves unavoidable loss of phase space density when the gravitational energy dominates the kinetic energy of the ensemble. In such a case the gravitational energy is transformed into heat, making a subsequent evaporation process slower and less efficient. We apply a high phase space loading scheme on a sub-doppler cooled ensemble of Rubidium atoms, with a gravitational energy much higher than its temperature of $1~\rm{\mu K}$. Using the regular configuration of a quadrupole magnetic trap, but driving unequal currents through the coils to allow the trap center to fall, we dissipate most of the gravitational energy and obtain a 20-fold improvement in the phase space density as compared to optimal loading into a static magnetic trap. Applying this scheme, we start an efficient and fast evaporation process as a result of the sub-second thermalization rate of the magnetically trapped ensemble.