Polariton condensation with nonlinear photons

In this paper we propose a model of polariton condensation with Kerr-type nonlinear photons. We introduce a generalized Dicke Hamiltonian to describe our system. By constructing the partition function as a path integral, the analytical and numerical solutions are presented. On the mean-field level, it is shown that the polariton condensation can occur and the Kerr nonlinearity affects the character of the polariton condensate. As the nonlinear coefficient increases, the condensate evolves from more photon-like to more exciton-like. Although the photon nonlinearity gives rise to a chemical potential greater than the photon energy, the quasiparticle excitation spectrum is still fully gapped. For the condensate collective excitations, the nonlinearity destroys the Goldstone modes and mixes the phase modes with the amplitude modes, resulting four non-zero-frequency collective modes. In addition, the influence of the photon-exciton detuning on the polariton condensate is also discussed.