High-resolution spectroscopy of single nitrogen-vacancy defects at zero magnetic field

Nitrogen-vacancy (NV) centers in diamond are excellent and versatile quantum sensors, even at room temperature and pressure. The extraordinary sensitivity of NV centers to the external and internal fields, including electric, magnetic, stress/strain fields and temperature, makes them susceptible to these perturbations, thus making the study of their effect on the NV centers essential. In this work, we discuss the effect of intrinsic electric and strain fields, collectively known as the effective field, on the energy level structure of the NV center. Our work is a vital step in understanding the consequence of the coupling of the NV center with its surrounding effective field.