High spatial resolution optical sensing with nitrogen vacancy center*

Quantum sensing with nanoscale resolution is a useful tool for nanoscience. Due to long spin coherence time and stable fluorescence, nitrogen vacancy (NV) center in diamond emerges as an important system for quantum sensing. Also, because of its sub-nanometer size, high spatial resolution is one of the most important advantages of the NV-based-sensing. By controlling the charge state transition between NV$^0$ and NV$^-$, we have developed a charge state depletion (CSD) nanoscopy on NV center to achieve sub-10nm spatial resolution with ultra-low pump power \footnote{ X.-D. Chen, et.al. Light-Sci. & Appl. 4, e230 (2015); X.-D. Chen, et.al. Phys. Rev. Appl. 7, 014008 (2017)}. Such a CSD nanoscopy has been applied to image the nanostructure with high spatial resolution. Moreover, by combining the CSD nanoscopy with fluorescence lifetime imaging microscopy, the optical density of a metal nanowire has been measured with sub-diffraction limit resolution. Since the NV center can also be applied in the sensing of electromagnetic field and temperature, a multi-function quantum sensor with nanoscale resolution can be achieved based on the CSD nanoscopy.