Polaritonics: from microcavities to sub‐wavelength confinement

Following the initial success of cavity quantum electrodynamics in atomic systems, strong coupling between light and matter excitations is now achieved in several solid‐state set‐ups. In those systems, the possibility to engineer quantum emitters and resonators with very different characteristics has allowed access to novel nonlinear and non‐perturbative phenomena of both fundamental and applied interest. In this article, we will review some advances in the field of solid‐state cavity quantum electrodynamics, focussing on the scaling of the relevant figures of merit in the transition from microcavities to sub‐wavelength confinement.