Achieving Ultralong Spin Coherent Time of Single Nitrogen Vacancy Centers in Diamond

Single negatively charged nitrogen vacancy (NV^-) centers in diamond have emerged as promising platforms for quantum information science, where long coherence times are essential for advancing quantum technologies. However, traditional fabrication methods often introduce lattice damage during the irradiation process used to create vacancies, significantly impairing the spin coherence properties of NV^- centers. In this study, we systematically investigate high-pressure/high-temperature (HPHT) annealing as a non-destructive approach to generate high-coherence single NV^- centers and elucidate the underlying mechanisms. Our results reveal that the distortion of the lattice field significantly influences the preferential formation of NV^- centers at the interface of the \langle 111\rangle-growth sector during diamond crystallization. Moreover, HPHT annealing effectively mobilizes nitrogen and vacancies, significantly promoting the formation of single NV^- centers. This process also mitigates the influence of the distortion of the lattice field, resulting in a marked enhancement of coherence properties, with T_2 times reaching 578 μs. Notably, a naturally formed single NV^- center in a low-stress region achieves an exceptional T_2 time of 721 μs, representing one of the highest values reported for diamonds with natural ^13C abundance. Building on these insights, we have successfully achieved controlled, large-scale fabrication of high-coherence single NV^- centers, providing essential guidance for future efforts to further enhance their coherence and establishing a robust foundation for their application in quantum technologies.