Abstract
The nitrogen-vacancy (NV) center in diamond has been established as a prime building block for quantum networks. However, scaling beyond a few network nodes is currently limited by low spin-photon entanglement rates, resulting from the NV center's low probability of coherent photon emission and collection. Integration into a cavity can boost both values 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 Purcell factors of up to 4, consistent with a detailed theoretical model. This model predicts that the probability of coherent photon detection per optical excitation can be increased to 10% for realistic parameters - an improvement over state-of-the art solid immersion lens collection systems by two orders of magnitude. The resonant operation of an improved optical interface for single coherent quantum emitters in a closed-cycle cryogenic system at T $\sim$ 4 K is an important result towards extensive quantum networks with long coherence.
Highlights
Future large-scale quantum networks sharing entanglement between their nodes may enable a suite of applications, such as secure communication, distributed quantum computation, and quantum enhanced sensing [1,2,3,4,5]
There are a number of changes that could improve zero-phonon line (ZPL) collection under resonant excitation; we focus on three main developments that have already been achieved in other systems
We demonstrate resonant excitation of cavity-coupled N-V centers with narrow optical transitions; the observed enhancement of collected coherent photons is in excellent agreement with our theoretical model
Summary
Future large-scale quantum networks sharing entanglement between their nodes may enable a suite of applications, such as secure communication, distributed quantum computation, and quantum enhanced sensing [1,2,3,4,5]. Entanglement generation rates are limited by the relatively low photon emission into the zero-phonon line (ZPL), as well as low collection efficiency from diamond, hindering scaling beyond a few nodes. Both values can be significantly increased by embedding the N-V center inside an optical cavity, making use of the Purcell effect. Poor optical coherence (approximately gigahertz linewidths), resulting from surface noise effects and/or implantationinduced damage, has so far prevented resonant optical addressing of Purcell-enhanced N-V centers [26,29,31,33, 35,36] This has presented a critical roadblock on the path towards remote entanglement generation. We conclude with an outlook including future prospects and avenues opened up by this work
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