Mainz 2026 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 33: Cavity QED, QED, and Spin-Boson Systems I

Q 33.8: Talk

Wednesday, March 4, 2026, 16:15–16:30, P 4

Cavity elimination in cavity-QED: a self-consistent and non-Markovian input-output theory — •Eliott Rambeau and Loic Lanco — Université Paris Cité, Centre de Nanosciences et de Nanotechnologies, 91120 Palaiseau, France

Simplifying composite open quantum systems, as cavity-QED ones, through model reduction is central to enable their analytical and numerical understanding. In this work, we introduce a self-consistent approach to eliminate the cavtiy degrees of freedom of cavity-QED devices in the non-adiabatic regime, where the cavity memory time is comparable with the timescales of the atom dynamics. We consider a cavity-QED system consisting of a two-level atom coupled to a single-mode cavity, both weakly interacting with the environment through an arbitrary number of ports, within the input-output formalism. We then derive a generalized Purcell formula and, under reasonable approximations, a consistent effective dynamics within a two-dimensional Hilbert space, allowing to simplify both analytical and numerical calculations. The resulting reduced model captures the non-Markovian features of the light-matter interaction, which we characterize through an effective Lindblad equation exhibiting a negative decoherence rate. In the continuous-wave excitation regime, we benchmark our approach by computing effective output flux formulas, correlations and spectral densities, showing an excellent agreement with full CQED simulations, except in the strong coupling high excitation regime. Our results provide a practical framework for reducing the size of a CQED system and could be generalized to more complicated structures.

Keywords: Cavity QED; Input output formalism; Light-matter interfaces; Hilbert space reduction; Open quantum system