Macroscopic quantum tunneling of a Bose condensate

Abstract

We study, by means of a variational method, the stability of a condensate in a megnetically trapped Bose gas with a negative scattering length and find that the condensate is unstable in general. However, for temperatures sufficiently close to the citical temperature the condensate turns out to be metastable. For that case we determine in the usual WKB approximation the decay rate of the condensate due to macroscopic quantum fluctuations. When appropiate, we also calculate the decay rate due to thermal fluctuations. An important feature of our approach is that (nonsingular) phase fluctuations of the condensate are taken into account exactly.