Dissipative quantum tunneling of two-state systems in metals

The transition rates of a two-state system in a metal are calculated as a function of the temperature T, the tunneling matrix element {Δ}, the asymmetry energy {ε}, the electron-defect coupling parameter K, and the phonon-defect coupling parameter U. Closed analytical expressions for the rates are obtained for parameters of relevance for recent experiments. Several earlier results are recovered as special cases. The predicted phonon effects should be readily observable.