  We study thermal emission of a cavity quantum electrodynamic system in the
ultrastrong-coupling regime where the atom-cavity coupling rate becomes
comparable the cavity resonance frequency. In this regime, the standard
descriptions of photodetection and dissipation fail. Following an approach that
was recently put forward by Ridolfo et al.[arXiv:1206.0944], we are able to
calculate the emission of systems with arbitrary strength of light matter
interaction, by expressing the electric field operator in the cavity-emitter
dressed basis. Here we present thermal photoluminescence spectra, calculated
for given temperatures and for different couplings in particular for available
circuit QED parameters.
