Visualized Axial Localization of Nitrogen-Vacancy Center in Bulk Diamond Assisted by Radially Polarized Beam

Nitrogen-vacancy (NV) centers in bulk diamond, as an excellent spin-based vector quantum sensor, require precise determination of the axis orientation information. Here, we efficiently visualize and completely determine the NV axis orientation in bulk diamond, assisted by a radially polarized beam. We observe the rotational asymmetric fluorescence pattern of NV centers in bulk diamond, which is quite different from that in nanodiamonds. Our theoretical calculations show this difference is mainly due to the fact that the ratio between the longitudinal and transverse electric field components of the focused radially polarized beam is greatly weakened in bulk diamond. This fluorescence pattern asymmetry can uniquely determine both the azimuth angle and the polar angle without degeneracy in bulk diamond. Then, we verify these theories in bulk diamond with different orientations and nanodiamonds. The experimental result is consistent with that of the traditional method by measuring a series of optically detected magnetic resonance (ODMR) spectra, and the error is less than 3.0 degrees. Our method can be easily extended to other solid-state spin systems and shows great potential in quantum sensing of vector magnetic fields and nanoscale dynamic processes.