Counteracting decoherence induced by spin-valley coupling in single-qubit manipulation zones via quantum optimal control

Quantum bus architectures based on electron spin shuttling in a Si/SiGe heterostructure are promising candidates for scalable quantum computing. Electrically controlled single qubit gates are achieved with a carefully placed micro-magnet that provides a synthetic spin-orbit coupling in the designated manipulation zones [Künne et al. arXiv:2306.16348 (2023)]. The presence of spin-valley hotspots at the vicinity of the micro-magnet can cause spin decoherence, limiting the capability to achieve fault tolerant gates. Using quantum optimal control techniques, we obtain new electron trajectories leading to significant improvements to the gate fidelity. The influence of valley splitting and the distance from spin-valley hotspots are also investigated, based on statistical sampling of prototypical device configurations. For increasing values of spin-valley coupling, 99.12% of the samples converged below the required fault tolerant gate fidelity threshold, where all of the under-performing samples are due to a high value of spin-valley coupling.