Quantum theory of optical bistability without adiabatic elimination

A quantum theory describing N two-level atoms in a coherently driven single-mode optical ring cavity is presented. The usual approximation that one may adiabatically eliminate either the cavity or atomic variables is not made. Hence the results are valid for a range of relative cavity and atomic relaxation rates. The theory is based on the linearized equations derived in the positive P representation. A simple analytical solution is presented, including the effect of detunings, for the steady-state transmitted spectrum. The transmitted intensity and squeezing spectra are discussed.