GAIN PRODUCED BY A 2-LEVEL ATOM IN CONTACT WITH A SQUEEZED BATH AND A COHERENT DRIVE

In Optics Comm. 110 (1994) 555, Ficek, Smyth and Swain consider a system comprising a two-level atom, a coherent drive field, a squeezed bath and a weak probe wave. They find a condition for achieving gain in the probe wave. In this paper, we show that their gain condition can be expressed as a condition among the derivatives of the atomic polarization vector with respect to the quadratures of the coherent drive. We then discuss this derivative condition in light of previous investigations that have considered such derivatives.