Polarons and Bose decondensation: A self-trapping approach

An additional, quantum, particle interacting with a Bose condensate forms self-trapped "polaron" if the interaction is sufficiently strong. This is contrasted with the case where the additional particle is identical with those in the condensate, where the "self-trapping" would be interpreted as a consequence of a Mott transition. There the transition to the self-trapped state, if it exists, is abrupt, unlike the impurity case. An external potential enhances self-trapping in the nonidentical ease.