Enhancement of NV-center coherence times via suppression of the surface noise in coated nanodiamonds.

The emergence of Nitrogen-Vacancy centers (NVs) as a candidate for quantum sensing and metrology has recently attracted significant attention in the quantum information science community. While it is optimal to have shallow NV to increase its sensitivity to the external signal, this conflicts with the rapid increase of the noise near the surface – decreasing the signal-to-noise ratio. Accordingly, efforts have been devoted to explore techniques aiming to reduce the surface noise.

In this work we first model and study the relevant noise sources for NVs implanted within nanodiamonds. Furthermore, we theoretically obtain the signatures of both surface and bulk noises on the evolution of NV-coherence. By contrasting these findings with our experimental data, we show that while the surface noise is the dominant source for bare nanodiamonds, silica-coated nanodimamonds show a dominant bulk noise source, thus evidencing a surface noise suppression via coating processes. This suppression produces a 3.5-fold increase in the NV-coherence time, thus opening a path for enhancing the sensitivity of NV in nanodiamond.