Decoherence properties of near-surface nitrogen-vacancies in diamond

Optically addressable spin-defects, such as the nitrogen-vacancy (NV) center in diamond, have emerged as potential quantum sensors with ultra-high sensitivity and sub-nm spatial resolution. The efficient utilization of quantum sensors requires the placement of the spin-defects in close proximity to the diamond surface, so as to strongly couple the defect with sensing targets. However, near-surface NV- centers are known to decohere significantly faster compared to their bulk counterparts indicating that the diamond surface introduces additional sources of noise, not present in the bulk material. To unravel the influence of the diamond surface on the coherence properties of NV centers in diamond, we performed a computational study of the coherence times of these centers as a function of the diamond surface orientation, reconstruction, and functionalization. Specifically, we combined cluster correlation expansion (CCE) and density functional theory calculations to estimate the Hahn-echo spin-coherence time of the NV centres at varying depth (< ca. 10 nm) from the surface. We used the Quantum Espresso and the pyCCE code [1] for DFT and CCE calculations, respectively.

Our results provide a theoretical upper bound of the coherence time for near-surface NV centers for a broad range of surface terminations and surface spin densities, giving important insights for the optimization of materials for diamond-based quantum sensors.