Fig. 3: Magnetic-field orientation and amplitude dependence of cwODMR.

a Angular magnetic-field dependence of cwODMR frequency (top panels) and contrast of resonances f_A to f_C (top to bottom), normalised by the zero-field cwODMR contrast of the f_B resonance, with 50-mT bias magnetic field applied in the yz plane. Data are presented as circles, with colour coding according to the inset of Fig. 1d, and curves indicate the cwODMR contrast simulated using the model of Fig. 2 and fit parameters presented in Tab.1. The inset indicates the direction of rotation of the bias magnetic field. b Calculated contrast of each resonance as a function of B_y and B_z. c as (a), but with 50-mT bias field applied in the xy plane of the defect (ϕ varies with fixed θ = 85°). d Calculated contrast of each resonance as a function of B_x and B_y. e Persistence of saturated cwODMR contrast for field applied along the defect y direction (ϕ = 90°, θ = 85°), shown up to 140 mT. The solid curves represent the transition frequencies of f_A (green), f_B (red), and f_C (blue) resonances as a function of B_y amplitude. The measured cwODMR contrast as a function of MW frequency is represented by blue circles. f Evolution of spin eigenstates of the Hamiltonian Eq. (1) with applied magnetic field along the x, y, z axes of the defect, from top to bottom. Calculated amplitudes of the optically initialised population of each spin sublevel are indicated by the size of the purple circles.