Realization of a single-Cooper-pair Josephson laser
Fei Chen, Juliang Li, Andrew D. Armour, Erind Brahimi, Joel Stettenheim, Adam J. Sirois, Raymond W. Simmonds, M. P. Blencowe, A. J. Rimberg · Physical Review B · 2014
The authors couple a microwave cavity to a voltage-biased Cooper-pair transistor, which emits photons at the Josephson frequency $\frac{2e\phantom{\rule{0}{0ex}}V}{\mathrm{\ensuremath{\Elzxh}}}$. If that frequency matches the cavity frequency, photons build up in it, which in turn creates back-action on the Cooper-pair transistor leading to stimulated rather than spontaneous tunneling.