REFORMULATION OF STEADY-STATE NONEQUILIBRIUM QUANTUM STATISTICAL-MECHANICS

Starting from the usual formulation of nonequilibrium quantum statistical mechanics, the expectation value of an operator A in a steady state nonequilibrium quantum system is shown to have the form [A]=Tr{e(-beta(H-Y))A}/Tr{e(-beta(H-Y))}, where H is the Hamiltonian, beta is the inverse of the temperature, and Y is an operator which depends on how the system is driven out of equilibrium. Because [A] is not expressed as a sum of correlation functions integrated over real time, one can now consider performing nonperturbative calculations in interacting nonequilibrium quantum problems.