Two-photon-interaction effects in the bad-cavity limit

Various experimental platforms have proven to be valid testbeds for the implementation of nondipolar light-matter interactions, where atomic systems and confined modes interact via two-photon couplings. Here, we study a damped quantum harmonic oscillator interacting with N two-level systems via a two-photon coupling in the so-called bad-cavity limit, in the presence of finite-temperature baths and coherent and incoherent drivings. We have succeeded in applying a recently developed adiabatic elimination technique to derive an effective master equation for the two-level systems, presenting two fundamental differences compared to the case of a dipolar interaction: an enhancement of the two-level systems spontaneouslike emission rate, including a thermal contribution and a quadratic term in the coherent driving, and an increment of the effective temperature perceived by the two-level systems. These differences give rise to striking effects in the two-level systems dynamics, including a faster generation of steady-state coherence and a richer dependence on temperature of the collective effects, which can be made stronger at higher temperature.