# Spin Measurements of NV Centers Coupled to a Photonic Crystal Cavity

## TL;DR

This study demonstrates that coupling NV centers in diamond to a photonic crystal cavity significantly enhances the signal-to-noise ratio of optical spin read-out, advancing quantum sensing and communication technologies.

## Contribution

The paper reports the fabrication of high-Q photonic crystal cavities in diamond and their integration with NV centers to improve spin read-out performance.

## Key findings

- ZPL emission enhanced by nearly tenfold on resonance
- SNR of spin read-out almost tripled with cavity coupling
- Cavities achieved Q-factors up to 8250 in diamond membranes

## Abstract

Nitrogen-vacancy (NV) centers feature outstanding properties like a spin coherence time of up to one second as well as a level structure offering the possibility to initialize, coherently manipulate and optically read-out the spin degree of freedom of the ground state. However, only about three percent of their photon emission are channeled into the zero phonon line (ZPL), limiting both the rate of indistinguishable single photons and the signal-to-noise ratio (SNR) of coherent spin-photon interfaces. We here report on the enhancement of the SNR of the optical spin read-out achieved by tuning the mode of a two-dimensional photonic crystal (PhC)cavity into resonance with the NV-ZPL. PhC cavities are fabricated by focused ion beam (FIB) milling in thin reactive ion (RIE) etched ultrapure single crystal diamond membranes featuring modes with Q-factors of up to 8250 at mode volumes below one cubic wavelength. NV centers are produced in the cavities in a controlled fashion by a high resolution atomic force microscope (AFM) implantation technique. On cavity resonance we observe a lifetime shortening from 9.0ns to 8.0ns as well as an enhancement of the ZPL emission by almost one order of magnitude. Although on resonance the collection efficiency of ZPL photons and the spin-dependent fluorescence contrast are reduced, the SNR of the optical spin read-out is almost tripled for the cavity-coupled NV centers.