Electronic structure, spin properties, and charge state stability of the negatively charged nickel vacancy center in diamond

Crystal defects in diamond, specifically the nitrogen vacancy (NV) and group-IV vacancy (SiV, GeV, SnV) centers have emerged as leading qubit candidates and have been used in several proof-of-principle experiments. However, they face several orthogonal challenges, with the NV's lack of symmetry limiting its optical properties and the group-IV vacancies electronic structure resulting in short coherence times. Recently, we have identified the nickel vacancy (NiV) to be a highly promising inversion-symmetric and electronically favorable defect to overcome these remaining limitations. Here, we report first steps towards making the NiV accessible for applications in quantum information processing. We demonstrate creation of NiV- centers in both type IIa and IIb diamond via ion-implantation and high-temperature high-pressure annealing. Using confocal magneto-optical fluorescence spectroscopy at temperatures down to 1.7K and up to 9T, we further characterize the NiV's optical properties, transition linewidths, and fluorescence lifetimes. Our studies broadly confirm the predicted electronic and spin properties and are consistent with our own group theoretical model as well as with recent density functional theoretical calculations. Finally, we investigate the center's charge state stability and ground state spin properties under various illumination and diamond substrate conditions, paving the way for all-optical spin control.