We show that a properly dc-biased Josephson junction in series with two microwave resonators of different frequencies emits photon pairs in the resonators. By measuring auto- and inter-correlations of the power leaking out of the resonators, we demonstrate two-mode amplitude squeezing below the classical limit. This non-classical microwave light emission is found to be in quantitative agreement with our theoretical predictions, up to an emission rate of 2 billion photon pairs per second.
@article{arxiv.1703.05009,
title = {Emission of non-classical radiation by inelastic Cooper pair tunneling},
author = {M. Westig and B. Kubala and O. Parlavecchio and Y. Mukharsky and C. Altimiras and P Joyez and D. Vion and P. Roche and M. Hofheinz and D Esteve and M Trif and P. Simon and J. Ankerhold and F. Portier},
journal= {arXiv preprint arXiv:1703.05009},
year = {2017}
}