Dual-frequency spin resonance spectroscopy of diamond nitrogen-vacancy centers in zero magnetic field

Abstract: The methods for controlling spin states of negatively charged nitrogen-vacancy (NV) centers using microwave (MW) or radiofrequency (RF) excitation fields for electron spin and nuclear spin transitions are effective in strong magnetic fields where a level anti-crossing (LAC) occurs. A LAC can also occur at zero field in the presence of transverse strain or electric fields in the diamond crystal, leading to mixing of the spin states. In this paper, we investigate zero-field LAC of NV centers using dual-frequency excitation spectroscopy. Under RF modulation of the spin states, we observe sideband transitions and Autler-Townes splitting in the optically detected magnetic resonance (ODMR) spectra. Numerical simulations show that the splitting originates from Landau-Zener transition between electron spin |$\pm$1> states, which potentially provides a new way of manipulating NV center spin states in zero or weak magnetic field.