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 w ith the environment is modeled by considering bath external noise disturban ce and nonlinear effects due to the contraction of the Hilbert space. The n oise alone produces decoherence and suppression of tunneling, but delocaliz ed states spontaneously evolve into localized ones only when nonlinearity i s also present. (C) 2000 Elsevier Science B.V. All rights reserved.