Field-driven dynamic charge stability of nitrogen vacancy centers near diamond-water interface

Negatively charged nitrogen vacancy (NV) centers in diamond are promising platforms for nanoscale quantum sensing, particularly in detecting single molecules in solution. However, solvents and electrical noise complicate these measurements, and the underlying molecular mechanisms are poorly understood. Here, we demonstrate how electrolytic solvents and applied electric fields influence the charge stability of NV centers in diamond using ab initio molecular dynamics simulations, hybrid density functional theory calculations, and the ab initio thermopotentiostat method. We find that the hydrophobicity of the diamond surface dictates the long-range electrostatic interactions between the electrolyte and the near-surface NV center, thereby impacting the charge state of NV centers. Additionally, applying external electric fields at the diamond-water interface enables conversion between the neutral and negatively charged states of NV centers via the Stark effect. These findings enhance our understanding of electrified interfaces of near-surface spin defects for quantum sensing applications.