Quantum noise in the parametric oscillator: From squeezed states to coherent-state superpositions

We compare the nonclassical states of light produced by a parametric oscillator for quantum noise of different strengths. Increasing noise strength brings a transition from a slightly perturbed classical state showing squeezing to a superposition of coherent states. We use the positive-P representation to illustrate the roles of quantum noise, quantum coherence, nonlinearity, and dissipation in this simple quantum dynamical system.