SELF-CONSISTENT GREENS-FUNCTION APPROACH TO DISSIPATIVE 2-STATE SYSTEM

We study the properties of a dissipative two-state fermionic system em bedded in a phonon bath at zero temperature. In contrast to the tradit ional path-integral and canonical transformation approaches, we propos e a self-consistent Green's function approach. Our results show that t he mean field theory overestimates the polarization of the system. To justify our approach, we consider a simplest case in which there is on ly one phonon mode. This simple model call be 'exactly' diagonalized. We find that the results from the serf-consistent Green's function app roach agree well with the quantum mechanical diagonalization results.