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 dissipation, and their dependence on the form of the coupling strength g(l) similar to omega(l)(lambda) (omega(l) is the phonon frequency) is analyzed. 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 find that the stable area of the displaced-squeezed state increases as lambda decreases.