Collective excitations, metastability, and nonlinear response of a trapped two-species Bose-Einstein condensate

We present a new theoretical treatment of the collective excitation spectrum of a two-species Bose-Einstein condensate confined in a magnetic trap, We show that the interspecies interaction significantly modifies th excitation spectrum and gives rise to a rich set of new phenomena. We identify a novel metastable stare of the double condensate and show that under external perturbation there can be a macroscopic quantum transition between this metastable state and the true ground state of the double condensate system. [S0031-9007(97)05175-2].