Efficient Coupling of an Ensemble of Nitrogen Vacancy Center to the Mode of a High-Q, Si3N4 Photonic Crystal Cavity

Integrated nanophotonics is an emerging field with high potential for quantum technology applications such as quantum sensing or quantum networks. A desired photonics platform is Si3N4 due to low-photon loss and well-established fabrication techniques. However, quantum optics applications are not yet established. Here, we investigate an approach toward Si3N4-based quantum photonics utilizing a crossed wave-guide, pump-probe design. The platform enables efficient, on-chip excitation, strong background suppression, and at the same time, efficient coupling to the mode of a high-Q photonic crystal cavity. The freestanding photonic crystal cavities reach high Q-factors up to 47 X 10(3). To test our platform, we positioned an ensemble of negatively charged nitrogen vacancy centers located in a nanodiamond within the interaction zone of the photonic crystal cavity. We quantify the efficiency of the coupling with the beta(lambda)-factor reaching values as large as 0.71. We further demonstrate on-chip excitation of the quantum emitter with strong suppression (similar to 20 dB) of the background fluorescence. Our results unfold the potential to utilize negatively charged nitrogen vacancy centers in nanodiamonds and Si3N4 platforms as an efficient, on-chip spin-photon interface in quantum photonics experiments.