Inelastic photon scattering via the intracavity Rydberg blockade
  Electromagnetically induced transparency (EIT) in a ladder system involving a Rydberg level is known to yield giant optical nonlinearities for the probe field, even in the few-photon regime. This enhancement is due to the strong dipole-dipole interactions between Rydberg atoms and the resulting excitation blockade phenomenon. In order to study such highly correlated media, ad hoc models or low-excitation assumptions are generally used to tackle their dynamical response to optical fields. Here, we study the behaviour of a cavity Rydberg-EIT setup in the non-equilibrium quantum field formalism, and we obtain analytic expressions for elastic and inelastic components of the cavity transmission spectrum, valid up to higher excitation numbers than previously achieved. This allows us to identify and interpret a polaritonic resonance structure, to our knowledge unreported so far. 
A. Grankin, E. Brion, R. Boddeda, S. \'Cuk, I. Usmani, A. Ourjoumtsev,   P. Grangier
quant-ph