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 Si 3 N 4 due to low-photon loss and well-established fabrication techniques. However, quantum optics applications are not yet established. Here, we investigate an approach toward Si 3 N 4 -based quantum photonics utilizing a crossed waveguide, 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 × 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 β λ -factor reaching values as large as 0.71. We further demonstrate on-chip excitation of the quantum emitter with strong suppression (∼20 dB) of the background fluorescence. Our results unfold the potential to utilize negatively charged nitrogen vacancy centers in nanodiamonds and Si 3 N 4 platforms as an efficient, on-chip spin-photon interface in quantum photonics experiments.