New defects in 4H-SiC with possible spin-qubit functionalities

We propose neutral defects in 4H-SiC comprising a silicon vacancy and a dopant substituting a carbon atom as a promising optically controllable qubit. According to our first principles calculations, the defect has two different atomic configurations, both have triplet and singlet ground states. Both configurations have close total energies, so they can coexist in the host. We apply the linear response GW method as well as the Bethe-Salpeter equation technique to calculate the optical excitation spectra for the triplet and singlet states of both configurations. Using the obtained data we build the optical spin-polarization cycles for the systems under consideration and find that both configurations of the proposed defect possess promising qubit functionality.