  We consider a Bose-Einstein bicondensate (BEC) of $^{87}Rb$, trapped in two
different internal levels, in a situation where the density undergoes a
symmetry breaking in momentum space. This occurs for a suitable number of
condensed atoms within a double well dispersion curve, obtained by Raman
coupling two internal states with two tilted and detuned light fields. Evidence
of bistability results from the Gross-Pitaevskii equation. By second
quantization, we evaluate the tunneling rate between the two asymmetric states;
the effects of losses on coherence are also considered.
