Lifetime-Limited and Tunable Emission from Charge-Stabilized Nickel Vacancy Centers in Diamond

The negatively charged nickel vacancy center (NiV$^-$) in diamond is a promising spin qubit candidate with predicted inversion symmetry, large ground state spin orbit splitting to limit phonon-induced decoherence, and emission in the near-infrared. Here, we experimentally confirm the proposed geometric and electronic structure of the NiV defect via magneto-optical spectroscopy. We characterize the optical properties and find a Debye-Waller factor of 0.62. Additionally, we engineer charge state stabilized defects using electrical bias in all-diamond p-i-p junctions. We measure a vanishing static dipole moment and no spectral diffusion, characteristic of inversion symmetry. Under bias, we observe stable transitions with lifetime limited linewidths as narrow as 16\,MHz and convenient frequency tuning of the emission via a second order Stark shift. Overall, this work provides a pathway towards coherent control of the NiV$^-$ and its use as a spin qubit and contributes to a more general understanding of charge dynamics experienced by defects in diamond.