Unexpected enhancement of quartet spin state relaxation in silicon carbide due to isotope purification

Spin defects and nuclear spins are often the major sources of decoherence and spin relaxation of solid-state qubits formed by optically addressable point defect spins in semiconductors. Understanding these inherently many-body phenomena is of crucial importance for advancing entanglement-based applications in solids. In our recent work, we utilize state-of-the-art theoretical tools to investigate dipolar spin relaxation and decoherence of a quartet spin qubit system provided by the negatively charged silicon vacancy point defect in silicon carbide. In particular, we study spin flip-flops at the zero-field region, where the quartet states are only slightly split due to the marginal zero-field interaction, and quantify relevant decay times at increased magnetic field values for various spin-active defect concentrations and nuclear spin abundances. Furthermore, we demonstrate that isotope purification, which reduces nuclear spin induced decoherence and spin relaxation interactions, also enhances the coupling of the quartet spin with neighboring spin-1/2 point defects through the elimination of local inhomogeneity of the host. This magnetic field independent effect can limit both the T₁ and the T₂ time in an unexpected way in realistic materials.