Figure 1

Main Figure: Schematics of the NV level scheme and of applied drivings. Green laser (green arrows) drives not-resonant optical spin-preserving transition from ground state(GS) to excited state(ES). Relaxation from ES to GS happens trough a radiative decay for states with \(m_{s}=0\), resulting in red photoluminescence (red-arrows). For the state with \(m_{s}=\pm 1\) relaxation happens either trough a radiative decay as in the previous case and trough a not-radiative decay involving a metastable state (MS) (dashed black lines). These results in a higher photoluminesce (turn-on lamp) for state with \(m_{s}=0\) compared to state with \(m_{s}=\pm 1\) (turn-off lamp). Populations of the spin staes can be varied by resonant microwave magnetic field (blue arrow) of frequency ν. A resonant magnetic field will increase the \(m_{s}=\pm 1\) state population causing a decrease in red photoluminesce. The application of a magnetic field removes the energy degeneracy between the \(m_{S}=\pm 1\) spin states, creating two separate resonance frequencies \(\nu _{-}\) and \(\nu _{+}\). Inset: Schematics of lock-in detection. The microwave signal is frequency modulated with an ampltude \(f_{\mathrm{dev}}\) at a frequency \(f_{\mathrm{mod}}\). \(f_{\mathrm{dev}}\), is equal to the full- width half maximum of the original ODMR signal. The resulting photoluminescence signal will be also modulated at frequency \(f_{\mathrm{mod}}\)