PROSPECTS FOR MIXED-ISOTOPE BOSE-EINSTEIN CONDENSATES IN RUBIDIUM

We calculate binary collision parameters for mixtures of ultracold gas es of Rb-85 and Rb-87 atoms. We predict a large positive triplet scatt ering length for mixed-isotope collisions, which implies that a stable mixed-isotope double condensate can be formed by sympathetic evaporat ive cooling. Moreover. collisions between Rb-85 and Rb-87 atoms in the lowest hyperfine manifold exhibit magnetic-field-induced Feshbach res onances which should allow partial control of the interaction between condensates. These considerations make Rb an ideal system for the stud y of interpenetrating bosonic superfluids.