Resonant Excitation and Purcell Enhancement of Coherent Nitrogen-Vacancy Centers Coupled to a Micro-Cavity

Quantum networks are promising both for applications like secure communication and for basic science tests of quantum mechanics at a large scale. The Nitrogen-Vacancy (NV) center in diamond is an excellent node candidate, because of its long spin coherence and accessible local qubit registers, but it has limited collectible coherent photon emission. Integration into a cavity can boost collection via the Purcell effect, but poor optical coherence of near-surface NV centers has so far prevented their resonant optical control, as would be required for entanglement generation. Here, we overcome this challenge, and demonstrate resonant addressing of individual, fiber-cavity-coupled NV centers, and collection of their Purcell-enhanced coherent photon emission. Utilizing off-resonant and resonant addressing protocols, we extract an enhancement of the zero-phonon line emission by a factor of up to 4, consistent with a detailed theoretical model. Based on our results and model, we project that with some realistic improvements NV centers in cavities can speed up entanglement generation in present day networks by at least a factor of 100, bringing large scale quantum networks with NV centers much closer.