Optical Schrödinger cat states in one mode and two coupled modes subject to environments

Taking the decoherence into account, we investigate nonclassical features of the optical Schr\"odinger cat states in one-mode and two-coupled-modes systems with two-photon driving. In the one-mode system, the relationship between the Schr\"odinger cat states and the system parameters is derived. We observe that in the presence of single-photon decay the steady states would be a mixture of Schr\"odinger cat states. The dynamics and steady states of such a cat versus single-photon decay are examined. In the two-coupled-modes cases with linear and nonlinear couplings, the dynamics of entanglement and mutual information are examined with two different initial states and single-photon decay. Compared to the linear coupling case, more complicated structure appears in the Wigner function in the nonlinear coupling case. The joint quadrature distributions are also explored. Such nonclassical states can be used not only in exploring the boundary between the classical and the quantum worlds but also in quantum metrology and quantum information processing.