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

Abstract

Key properties of nine possible defect sites in hexagonal boron nitride (h-BN), ${V}_{\mathrm{N}},{{V}_{\mathrm{N}}}^{\ensuremath{-}1},{\mathrm{C}}_{\mathrm{N}},{V}_{\mathrm{N}}{\mathrm{O}}_{2\mathrm{B}},{V}_{\mathrm{N}}{\mathrm{N}}_{\mathrm{B}},{V}_{\mathrm{N}}{\mathrm{C}}_{\mathrm{B}},{V}_{\mathrm{B}}{C}_{\mathrm{N}},{V}_{\mathrm{B}}{\mathrm{C}}_{\mathrm{N}}\mathrm{S}{\mathrm{i}}_{\mathrm{N}}$, and ${V}_{\mathrm{N}}{\mathrm{C}}_{\mathrm{B}}\mathrm{S}{\mathrm{i}}_{\mathrm{B}}$, 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 ${V}_{\mathrm{N}},{\mathrm{C}}_{\mathrm{N}}$, and ${V}_{\mathrm{N}}{\mathrm{O}}_{2\mathrm{B}}$, respectively, while the observed photoemission at 1.95 eV is assigned to ${V}_{\mathrm{N}}{\mathrm{C}}_{\mathrm{B}}$. Detailed consideration of the available excited states, allowed spin-orbit couplings, zero-field splitting, and optical transitions is made for the two related defects ${V}_{\mathrm{N}}{\mathrm{C}}_{\mathrm{B}}$ and ${V}_{\mathrm{B}}{C}_{\mathrm{N}}$. ${V}_{\mathrm{N}}{\mathrm{C}}_{\mathrm{B}}$ is proposed for realizing long-lived quantum memory in h-BN. ${V}_{\mathrm{B}}{C}_{\mathrm{N}}$ 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.