Electroluminescence, the emission of light in the presence of an electric current, provides information on the allowed electronic transitions of a given system. Our work shows that, together with usual electroluminescence, systems in the ultrastrong light-matter coupling regime emit a uniquely quantum radiation when a flow of current is driven through them. While standard electroluminescence relies on spontaneous emission from excited states of the system, the process we describe extracts bound photons from the dressed ground state and it has peculiar features that unequivocally distinguish it from usual electroluminescence.

Reference: http://arxiv.org/abs/1508.05849.