QUANTUM DIFFUSION AND TUNNELING WITH PARAMETRIC BANDED RANDOM-MATRIX HAMILTONIANS

The microscopic origin of dissipation of a driven quantum many-body sy stem is addressed in the framework of a parametric banded random matri x approach. We find noticeable violations of the fluctuation-dissipati on theorem and we observe also that the energy diffusion has a markedl y non-Gaussian character. Within the Feynman-Vernon path integral form alism and in the Markovian limit, we further consider the time evoluti on of a slow subsystem coupled to such a 'bath' of intrinsic degrees o f freedom. We show that dissipation leads to qualitative modifications of the time evolution of the density matrix of the slow subsystem. In either the spatial, momentum or energy representation the density dis tribution acquires very long tails and tunneling is greatly enhanced. (C) 1997 Elsevier Science Ltd.