Stability and decoherence analysis of the silicon vacancy in 3C-SiC

The silicon vacancy (VSi) in 3C-SiC is studied as a center of interest in the field of quantum technologies, modeled as an electron spin (behaving as a two-state qubit in appropriate conditions) interacting through hyperfine coupling with the SiC nuclear spin bath containing Si29 and C13 nuclei in their natural isotopic concentration. We calculate the formation energies of the neutral and charged VSi with ab initio methods based on the density functional theory, identifying the stability of the neutral charge state for energies close to the valence band of 3C-SiC. In addition, magnetic properties are calculated for the VSi-1 in 3C-SiC and for VSi0 in both cubic and hexagonal SiC polytypes. We thereon evaluate, for the defect in the cubic polytype, the free induction decay and the Hahn-echo sequence on the electron spin interacting with the nuclear spin bath, shedding light on the electron spin-echo envelope modulation phenomenon and the decoherence effect by means of the cluster correlation expansion theory. We find a nonexponential coherence decay, which is a typical feature of solid-state qubits subjected to low-frequency 1/f-type noise from the environment.