Nonclassical photon statistics and photon squeezing in the dissipative mixed quantum Rabi model

Nonclassical two-photon statistics and photon squeezing are considered as representative features of the nonclassicality of light. In this work we investigate two-photon correlation function and quadrature photon squeezing in the dissipative mixed quantum Rabi model (QRM), which includes both the one-photon and two-photon qubit-resonator interactions. The quantum dressed master equation combined with squeezed-coherent states is applied to obtain the steady state. Based on the zero-time delay two-photon correlation function, it is found that with the increase of the two-photon qubit-resonator interaction strength the photon antibunching behavior is monotonically suppressed, whereas the photon bunching signature persists. One additional giant photon bunching feature is unraveled at deep-strong two-photon coupling, which mainly stems from efficient successive transition trajectories. The finite-time delay two-photon correlation function asymptotically approaches the unit by raising the delayed time. Moreover, the steady-state quadrature photon squeezing becomes significant at strong two-photon coupling, which may become perfect in the zero temperature limit.