QUANTUM-MECHANICS AND THERMAL NOISE IN DISSIPATIVE SYSTEMS

We study the density matrix for systems with an arbitrary linear dissipative mechanism at finite temperature. We show how one may derive the tunneling Lagrangians using general methods in statistical mechanics. The derivation is phenomenological in nature and as such does not proceed from any particular microphysical description of a heat bath. Correspondingly, it is also a more general framework for studying other types of noise in quantum mechanical systems. For the special case of a linearly dissipative system we explicitly show how this method yields the formulae of Grabert et al. (Grabert, Weiss, and Hanggi. Phys. Rev. Lett.52 (1984), 2193; Grabert, Olschowski, and Weiss, Phys. Rev. B36 (1981), 1931). The appendix is a description of the phenomenological approach starting with a particular microphysical model of a linearly dissipative system. © 1993 Academic Press, Inc.