Superconducting cavity bus for single nitrogen-vacancy defect centers in diamond

Circuit-QED has demonstrated very strong coupling between light and matter, and has the potential to engineer large quantum devices. Hybrid designs have been proposed which couple large ensembles of atomic and molecular systems to the superconducting resonator. We show that one can achieve an effective strong coupling between light and matter for much smaller ensembles (and even a single electronic spin), through the use of an interconnecting quantum system: in our case a persistent current qubit. Using this interconnect we show that one can effectively magnify the coupling strength between the light and matter by over five orders of magnitude g∼7 Hz→100 kHz and enter a regime where a single nitrogen-vacancy (NV) electronic spin can shift the cavity resonance line by over ∼20 linewidths. With such strong coupling between an individual electronic spin in an NV and the light in the resonator, one has the potential build devices where the associated NV nuclear spins can be strongly coupled over centimeters via the superconducting bus.