Since their first synthesis in 2015 [1], perovskite quantum dots (pQDs) have revealed their potential as scalable solid-state quantum emitters, combining bright emission, high-purity single photon generation at room temperature [2], and even photon indistinguishability with 50% visibility at cryogenic temperatures [3]. Coupling individual pQDs to optimized photonic structures in order to control and enhance their emission via cavity quantum electrodynamics (cQED) effects is now a crucial objective. In this context, a prerequisite is the precise characterization of key cQED metrics. The most challenging ones for solid-state emitters are the light-matter vacuum Rabi coupling strength and the homogeneous linewidth, the latter being typically blurred by spectral diffusion in standard photoluminescence measurements.

In this talk, I will present a linear cQED approach that delineates the respective contributions of pure dephasing and spectral diffusion to the emitter linewidth, without relying on quadratic photon correlation techniques, which often suffer from low signal-to-noise ratio [4]. Our method is based on a fully tunable cavity-emitter platform that enables the deterministic and reversible coupling of individual CsPbBr₃ pQDs to an open fiber Fabry-Pérot microcavity [5]. This allows us to study the very same pQD in both free space and cavity configurations while keeping its environment and excitation conditions unchanged, thereby eliminating the statistical biases inherent to monolithic photonic structures where spatial and spectral matching cannot be adjusted.
 
First, time-resolved photoluminescence experiments reveal up to a twofold increase in single photon emission rates by Purcell effect in the cavity configuration, corresponding to a Purcell factor of ~3.3. Then, by exploiting the cavity tunability, we study the cavity-induced reshaping of the multiplet excitonic fine structure and show that it provides a sensitive fingerprint of the light-matter coupling strength. Finally, combining these detailed temporal and spectral investigations enables a reliable determination of cQED parameters by crossing the constraints imposed by the two independent datasets, allowing us to extract both the homogeneous linewidth (~250 +/- 50 μeV, free of spectral diffusion) and a vacuum Rabi coupling strength up to 40 +/- 10 μeV for the smallest cavity mode volume.

Overall, I will present a robust framework for quantifying light-matter interaction in nano-emitters dominated by spectral diffusion, and I will show that the strong coupling regime is within reach with optimized pQDs and reduced cavity volumes.