Environmental control of quantum sensors: the case of nitrogen-vacancy centers in diamond

Quantum sensing with nitrogen vacancy (NV) center in diamond is an emerging technology to detect nuclear spins and chemical species with nearly atomistic resolution. This is achieved by translating the magnetic- and electric-field fluctuations from the respective sources directly to an optical signal, detected by a change in the fluorescence intensity of the NV center. In this work, we develop realistic models of the diamond-solvent interfaces to elucidate new sensing applications for the NV center, which are based on the reversible variations in the surface potential. More specifically, we show that aqueous diamagnetic electrolyte solutions such as sodium chloride can be sensed by an increase of the spin relaxation time of near-surface NV-center ensembles. Our first principles calculations combined with interface modeling identify a critical role of the interfacial band bending which leads to a stabilization of fluctuating charges at the interface of an oxygen-terminated diamond. In addition, we demonstrate that aqueous environment enables to recover a contrast in the optically detected magnetic resonance experiment for the shallow NV centers at cryogenic temperatures. Both predicted phenomena were directly confirmed in experiments by observing the optically detected magnetic resonance and spin relaxation times of the ensemble and single NV-centers.