Effective localization induced by noise and nonlinearity

With the aid of a very simple model with only two possible configurations, we study the dynamical transition from delocalized to localized states for quantum bistable systems. Results may have relevance for the understanding of the phenomenology of some mesoscopic systems which are usually found in a localized state as for example pyramidal AsH3 molecule. The interaction with the environment is modeled by considering both external noise disturbance and nonlinear effects due to the contraction of the Hilbert space. The noise alone produces decoherence and suppression of tunneling, but delocalized states spontaneously evolve into localized ones only when nonlinearity is also present.