LAUSR

Coupled localized electron spins hosted by defects in semiconductors implement quantum bits with the potential to revolutionize nanoscale sensors and quantum information processing. The present understanding of optical means of spin state manipulation and read-out calls for quantitative theoretical description of the active states, built-up from correlated electrons in a bath of extended electron states. Hitherto we propose a first-principles scheme based on many body perturbation theory and configuration interaction and address two room temperature point defect qubits, the nitrogen vacancy in diamond and the divacancy in silicon carbide. We provide a complete quantitative description of the electronic structure and analyze the crossings and local minima of the energy surface of triplet and singlet states. Our numerical results not only extend the knowledge of the spin-dependent optical cycle of these defects, but also demonstrate the potential of our method for quantitative theoretical studies of point defect qubits.Point defects: The whole pictureThe electronic states of point defects in semiconductors can be studied via first principles, suitable for large systems with thousands of electrons. The nitrogen-vacancy centre in diamond and the divacancy complex in silicon carbide are promising candidates for quantum applications. The non-radiative decay from their optically allowed excited states is pivotal to initializing and reading their spin. Michel Bockstedte and colleagues now model the electronic states of these defects using a method that relies on many-body theory and is free of empirical parameters. They map the optical transitions, as well as the spin relaxation dynamics and the role of the spin-orbit and electron-phonon coupling interactions involved, in good agreement with experimental data. The method is suitable for large systems, and can therefore be used to model qubits in other semiconductors.