title: Photon blockade in the ultrastrong coupling regime.
abstract: We explore photon coincidence counting statistics in the ultrastrong coupling regime, where the atom-cavity coupling rate becomes comparable to the cavity resonance frequency. In this regime, usual normal order correlation functions fail to describe the output photon statistics. By expressing the electric-field operator in the cavity-emitter dressed basis, we are able to propose correlation functions that are valid for arbitrary degrees of light-matter interaction. Our results show that the standard photon blockade scenario is significantly modified for ultrastrong coupling. We observe parametric processes even for two-level emitters and temporal oscillations of intensity correlation functions at a frequency given by the ultrastrong photon emitter coupling. These effects can be traced back to the presence of two-photon cascade decays induced by counterrotating interaction terms.
authors.affiliation: Physik Department, Technische Universität München, James-Franck-Strasse, 85748 Garching, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Ridolfo
authors.forename: M
authors.initials: M
authors.lastname: Leib
authors.forename: S
authors.initials: S
authors.lastname: Savasta
authors.forename: M J
authors.initials: MJ
authors.lastname: Hartmann