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), VN,VN-1,CN,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 VN,CN, 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.