DISSIPATIVE 2-STATE SYSTEM AT NONEQUILIBRIUM - REAL-TIME GREENS-FUNCTION APPROACH

In this paper Ne study the dynamical properties of a dissipative two-s tate fermionic system embedded in a phonon bath at finite temperature. The non-equilibrium thermo field dynamics, a real time formalism of t hermal quantum field theory, is employed to formulate time dependent e nergy renormalization and derive transport equations. The renormalizat ion procedures derived in this paper replace the on-shell energy defin itions in stationary situations and thus can be used in any situations . The procedure reduces to that of equilibrium situations when there i s no time dependence. We show that in a system where there are many co upled stages (with multi-components) quantum fluctuations among these states cannot be eliminated so that the long time limit of non-equilib rium theory does not exactly reproduce an equilibrium theory. The proc edures and conclusions obtained also apply to more general systems wit h multi-components.