Variability of Electron and Hole Spin Qubits Due to Interface Roughness and Charge Traps

Semiconductor spin qubits may show significant device-to-device variability in the presence of spinorbit coupling mechanisms. Interface roughness, charge traps, layout, or process inhomogeneities indeed shape the real-space wave functions, and hence the spin properties. It is, therefore, necessary to understand how reproducible the qubits can be, in order to assess strategies to cope with variability, and to set constraints on the quality of materials and fabrication. Here we model the variability of single-qubit properties (Larmor and Rabi frequencies) due to disorder at the Si/SiO2 interface (roughness, charge traps) in metal-oxide-semiconductor devices. We consider both electron qubits (with synthetic spin-orbit coupling fields created by micromagnets) and hole qubits (with intrinsic spin-orbit coupling). We show that charge traps are much more limiting than interface roughness, and can scatter Rabi frequencies over one order of magnitude. We discuss the implications for the design of spin qubits and for the choice of materials.