Theory of the neutral nitrogen-vacancy center in diamond and its application to the realization of a qubit

The negatively charged nitrogen-vacancy defect $({\text{NV}}^{\ensuremath{-}})$ in diamond has attracted much attention in recent years in qubit and biological applications. The negative charge is donated from nearby nitrogen donors that could limit or stem the successful application of ${\text{NV}}^{\ensuremath{-}}$. In this study, we identify the neutral nitrogen-vacancy defect $({\text{NV}}^{0})$ by ab initio supercell calculations through the comparison of the measured and calculated hyperfine tensors of the ${^{4}A}_{2}$ excited state. Our analysis shows that (i) the spin state can be selectively occupied optically, (ii) the electron spin state can be manipulated by time-varying magnetic field, and (iii) the spin state may be read out optically. Based on this ${\text{NV}}^{0}$ is a hope for realizing qubit in diamond without the need of nitrogen donors. In addition, we propose that ${\text{NV}}^{0}$ may be more sensitive magnetometer than the ultrasensitive ${\text{NV}}^{\ensuremath{-}}$.