Identifying and mitigating charge instabilities in shallow diamond nitrogen-vacancy centers

The charge degree of freedom in solid-state defects fundamentally underpins the electronic spin degree of freedom, a workhorse of quantum technologies. Here we study charge state properties of individual near-surface nitrogen-vacancy (NV) centers in diamond, where NV$^{-}$ hosts the metrologically relevant electron spin. We find that NV$^{-}$ initialization fidelity varies between individual centers and over time, and we alleviate the deleterious effects of reduced NV$^{-}$ initialization fidelity via logic-based initialization. We also find that NV$^{-}$ can ionize in the dark, which compromises spin measurements but is mitigated by measurement protocols we present here. We identify tunneling to a single, local electron trap as the mechanism for ionization in the dark and we develop NV-assisted techniques to control and readout the trap charge state. Our understanding and command of the NV's local electrostatic environment will simultaneously guide materials design and provide novel functionalities with NV centers.