Spin-exchange collision cooling in an ultracold $^{85}$Rb/$^{87}$Rb Mixture

We have confined ultracold $^{85}$Rb and $^{87}$Rb simultaneously in an optical trap. Through optical pumping, spin-exchange collisions between $^{85}$Rb and $^{87}$Rb in a magnetic field can be made to be endothermic, transferring kinetic energy to Zeeman energy. Subsequent optical pumping removes the Zeeman energy from the gas, cooling it without requiring atom loss. We describe our implementation of this cooling scheme\footnote{G. Ferrari, European Physical Journal D 13, 67-70 (2001).} and describe our experimental observations and characterizations of this cooling. We also discuss the advantages of using two different types of atoms in the cooling.