Laser writing with a solid immersion lens: towards optically coherent nitrogen-vacancy centers in microstructured diamond

An open Fabry-Perot microcavity coupled to a negatively charged nitrogen-vacancy center (NV) in diamond is a promising spin-photon interface [1-4]. Implementation of diamond into the system requires thinning it down to ~µm thickness while maintaining the NV optical coherence, a well-known challenge with standard NV creation methods. Initial studies on laser writing of NVs yielded promising results, but relied on a narrow window of parameters for successful writing [5]. We widen this window by using a solid immersion lens (SIL), which not only facilitates laser writing over a broad range of pulse energies, but also allows for vacancy formation close to a diamond surface without inducing surface graphitization. We present NV arrays that have been created between 1 and 40 µm from a diamond surface, presenting optical linewidth distributions with means as low as 61.0 MHz, including spectral diffusion induced by off-resonant repump. This emphasizes the exceptionally low charge-noise environment of laser-written NVs – a crucial prerequisite for the realization of distributed quantum networks based on spins in diamond.
[1] J. Appl. Phys 110, 053107 (2011)
[2] New J. Phys. 17, 122003 (2015)
[3] Phys. Rev. Lett. 110, 243602 (2013)
[4] Phys. Rev. X 7, 1 (2017)
[5] Nat. Photonics 11, 77 (2017)