Maître de conférences Bruno Bellomo

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

Atomic systems interacting with confined photonic or phononic modes represent one of the most studied classes of quantum-optical systems. It has been recently predicted that using solid-state or atomic systems it is possible to implement nondipolar light-matter couplings, where the linear interaction is inhibited and quantum emitters and localized bosonic modes interact via the exchange of two-excitation quanta. In particular, such two-photon couplings can be observed by engineering superconducting atom-resonator systems or by applying analog quantum simulation schemes in trapped-ion or ultracold-atom systems. Here, we consider a damped quantum harmonic oscillator interacting with N two-level systems via a two-photon coupling in the so called bad-cavity limit, aiming to compare this configuration with the dipolar case characterized by a one-photon coupling. We suppose that the harmonic oscillator and each two-level system are each in contact with an independent thermal bath at finite temperature T (equal for all baths) and that a resonant coherent pumping on the harmonic oscillator and an incoherent local pumping on the two-level systems are available [1]. 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 [1]. Our analytical and numerical analysis of the time evolution and steady-state behavior unveils indeed an unexpected phenomenology induced by nondipolar light-matter interactions. Compared to the dipolar case, the differences in the effective master equation give rise to striking effects in the two-level systems dynamics, including a faster generation of steady-state coherence and a richer dependence on the temperature T of the collective effects, which can be made stronger by increasing T [1]. We finally remark that the models here investigated can be feasibly implemented with both solid-state and atomic existing quantum technologies. [1] N. Piccione, S. Felicetti, and B. Bellomo, Phys. Rev. A 105, L011702 (2022).