The interaction between two species of atoms in the condensate has been deduced and the trial wave functions that conserve the total spin have been constructed for the states of the ground band. A couple of generalized Gross-Pitaevskii equations have been derived for the spatial wave functions and the energies. The mixture of ${}^{23}\mathrm{Na}$ and ${}^{87}\mathrm{Rb}$ has been calculated as an example. The density of states is found to exhibit a ladder shape.

• Received 5 February 2007

DOI:https://doi.org/10.1103/PhysRevA.75.043609