Decay of symmetry-protected quantum states

We study the decay of bosonic many-body states in the triple-well Bose-Hubbard model where bosons in the central well can escape into a reservoir. For vanishing interparticle interaction this system supports a nondecaying many-body state which is the antisymmetric Bose-Einstein condensate with particles occupying only the edge wells. In the classical approach this quantum state corresponds to a symmetry-protected nondecaying state which is stable even at finite interaction below a certain intensity threshold. Here we demonstrate that despite the fact that the classical counterpart is stable the antisymmetric Bose-Einstein condensate is always metastable at finite interatomic interactions due to quantum fluctuations.