Enhancing Fluorescence of Shallow Nitrogen-Vacancy Centers in Diamond by Surface Coating with Titanium Oxide Layers

We present an enhancement of the fluorescence of shallow (<10 nm) nitrogen-vacancy (NV^-) centers by using atomic layer deposition to deposit titanium oxide layers on the diamond surface. In this way, the shallow NV^- center charge states were stabilized, leading to the increasing fluorescence intensity of about 2 times. This surface coating technique could produce a protective layer of controllable thickness without any damages to the solid-state quantum system surface, which might be an approach to the further passivation or packaging techniques for the solid-state quantum devices.