Fig. 1: A ground-state spin triplet.

a, An ODMR spectrum of a single defect in hBN measured in the absence of a magnetic field. The top-right inset shows a confocal image of the PL intensity of the hBN device under 532 nm laser illumination. Scale bar, 0–300 kcps. The bottom-right inset shows the measurement sequence. b, ODMR resonance frequencies for a defect, where the magnetic field is applied in the plane of the hBN layers along the defect z axis (θ₀ = 0°) (purple circles) and 60° from the z axis (θ₀ = 60°) (pink circles). Both measurements are fit with an S = 1 model using equation (1) (purple and pink curves, respectively). The inset defines the orientation of the magnetic field relative to the defect z axis and the hBN layers, identified by θ₀. c, Inferred level structure for the defect, displaying a spin-triplet ground state and a spin-singlet metastable state. The green arrows show optical excitation; yellow arrows, PL; black arrows, intersystem crossing; and pink arrows, microwave (MW) drive. d,e, Statistical distribution of the D and E zero-field splitting parameters obtained from 25 defects. f, Spin–lattice relaxation time (T₁) measurement of the ground-state spin, measured in the absence of a magnetic field. The inset shows the microwave measurement sequence (not drawn to scale), where r is the reference readout, s is the signal readout and t is the pulse delay. g, Second-order intensity-correlation measurement (g⁽²⁾(t)) of a single defect.