Production of Two Overlapping Bose-Einstein Condensates by Sympathetic Cooling

A new apparatus featuring a double magneto-optic trap and an Ioffe-type magnetic trap was used to create condensates of $2\times {10}^6$ atoms in either of the $|F=2,m=2\mathrm{}〉$ or $|F=1,m=-1\mathrm{}〉$ spin states of ${}^{87}$Rb. Overlapping condensates of the two states were also created using nearly lossless sympathetic cooling of one state via thermal contact with the other evaporatively cooled state. We observed that (i) the scattering length of the $|1,-1〉$ state is positive, (ii) the rate constant for binary inelastic collisions between the two states is $2.2\left(9\right)\times {10}^{-14\mathrm{}}{\mathrm{cm}}^3/\mathrm{s}$, and (iii) there is a repulsive interaction between the two condensates. Similarities and differences between the behaviors of the two spin states are observed.