Localization induced by noise and non linearity

We introduce a model for a two configurations system, and we study the transition from quantum to classical behaviour. We first consider the effect of the interaction with the environment as an external noise and we show that it produces decoherence and suppression of tunnelling. These features are widely accepted as definition of classicality, while we believe that classicality implies that quantum delocalized states spontaneously evolve into localized ones. We than show that this evolution take place only when both noise and non linearity in the equations are present.