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The negatively charged nitrogen-vacancy (NV) center in diamond is among the most promising solid-state systems implementations of a quantum bit. However, integration of the NV center into any efficient photonic environment requires microstructuring the diamond at below-micrometer scale. Preserving the low NV zero-phonon line inhomogeneous broadening during this process is a major challenge with standard NV creation methods. This issue severely limits practical applications of NV centers.
Initial studies on pulsed-laser assisted creation of NVs yielded promising results by creating NVs with low inhomogeneous broadening at desired spatial locations in diamond [1]. Crucially, the lattice damage resulting from implantation of energetic ions was avoided. However, the method relied on a narrow window of parameters for successful writing. We widen this window by using a solid immersion lens (SIL), which facilitates laser writing over a broad range of pulse energies and allows for vacancy formation close to a diamond surface without inducing surface graphitization. We operate in the previously unexplored regime where lattice vacancies are created following tunneling breakdown rather than multiphoton ionization [2]. We present NV arrays that have been created between 1 and 40 µm from a diamond surface, all presenting optical linewidth distributions with means as low as 61.0±22.8 MHz [2], including spectral diffusion induced by off-resonant repump for charge stabilization. This emphasizes the exceptionally low charge-noise environment of laser-written NVs. Such high-quality NV centers are excellent candidates for practical applications employing two-photon quantum interference with separate NV centers.
Finally, we propose a model for disentangling power broadening from inhomogeneous broadening in the NV zero-phonon line optical linewidth [2].
[1] Y.-C. Chen, P. S. Salter, S. Knauer, … and J. M. Smith, Nat. Photonics 11, 77 (2017).
[2] V. Yurgens, J.A Zuber, S. Flågan, M. De Luca, B.J. Shields, I. Zardo, P. Maletinsky, R.J. Warburton, and T. Jakubczyk, ACS Photonics 8, 1726–1734 (2021)
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