Low-lying excitations of double Bose-Einstein condensates

We present the excitation spectrum of a double Bose-Einstein condensate for the JILA time orbiting potential trap including the effects of gravity. We consider two cases: (i) fixed scattering lengths and equal numbers of each atomic species as a function of the number of atoms and (ii) fixed intraspecies scattering lengths and a fixed, equal number of atoms in each state as a function of interspecies scattering length. The spectra reveal the rich dynamics of the system and in particular show simultaneous collective excitations of both condensates. [S1050-2947(98)06302-1].