Defect states in hexagonal boron nitride: Assignments of observed properties and prediction of properties relevant to quantum computation

Key properties of nine possible defect sites in hexagonal boron nitride (h-BN), V-N, V-N(-1), C-N, VNO2B, VNNB, VNCB, VBCN, VBCNSiN, and VNCBSiB, are predicted using density-functional theory and are corrected by applying results from high-level ab initio calculations. Observed h-BN electron-paramagnetic resonance signals at 22.4, 20.83, and 352.70 MHz are assigned to V-N, C-N, and VNO2B, respectively, while the observed photoemission at 1.95 eV is assigned to VNCB. Detailed consideration of the available excited states, allowed spin-orbit couplings, zero-field splitting, and optical transitions is made for the two related defects VNCB and VBCN. VNCB is proposed for realizing long-lived quantum memory in h-BN. VBCN is predicted to have a triplet ground state, implying that spin initialization by optical means is feasible and suitable optical excitations are identified, making this defect of interest for possible quantum-qubit operations.