VARIATIONAL STUDY OF DISSIPATIVE 2-STATE SYSTEMS

Two variational states, the displaced state and the displaced-squeezed state, are compared for a two-state system with super-Ohmic dissipati on, and their dependence on the form of the coupling strength g(l) sim ilar to omega(l)(lambda) (omega(l) is the phonon frequency) is analyze d. We find that, in the strong-coupling region, the displaced-squeezed state is more stable and the ground-state properties depend not only on the spectral density but also on the index lambda. Moreover, we fin d that the stable area of the displaced-squeezed state increases as la mbda decreases.