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

Abstract

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 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 × 10³. 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 Si₃N₄ platforms as an efficient, on-chip spin-photon interface in quantum photonics experiments.