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.