Spin measurements of NV centers coupled to a photonic crystal cavity

Abstract

Nitrogen-vacancy (NV) centers feature outstanding properties such as a spin coherence time of up to 1 s 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 3% of their photon emission is 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 milling in thin reactive ion 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 implantation technique. On cavity resonance, we observe a lifetime shortening from 9.0 ns to 8.0 ns 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.