ROLE OF COLLISIONS IN CREATION OF OVERLAPPING BOSE CONDENSATES

We study the elastic scattering length and inelastic decay rate associ ated with collisions of Na-23 and Rb-87 atoms in different hyperfine s tates: one with atoms in the \f=2, m(f)=2] and one with atoms in the \ f=1, m(f)=-1] state. For Na the real part of the a((22)+(1-1)) scatter ing length for \22] + \1-1] collisions is predicted to be positive and equal to 65+/-5 Bohr length units a(0) for small B. The zero-temperat ure low-field decay rate is of the order of a typical exchange rate: G ((22)+(1-1))=(1.5+/-0.7) 10(-11) cm(3) s(-1), showing that a two-conde nsate experiment is not feasible for a Na gas sample in a static magne tic trap. For the case of Rb atoms the present knowledge of the single t interaction does not allow a similar calculation. The extreme suppre ssion of G((22)+(1-1)) demonstrated by a recent experiment is shown to be very restrictive for the value of the singlet accumulated phase.