Variability in Si/SiGe and Si/SiO2 Spin Qubits Due to Interfacial Disorder

Silicon provides a promising platform to host solid-state spin qubits owing to long coherence times through isotopic purification and the highly advanced level of development in material processing and fabrication techniques. In practice, the uniformity of spin qubits is limited by uncontrolled atomistic fluctuations at the interface between the semiconductor and the confining material. Maintaining a qubit fidelity well above the quantum fault-tolerance threshold is only possible for a clean and well-defined two state system and accounting for the specific parameters of each qubit would quickly become a bottleneck for any large-scale quantum computer. Despite extensive efforts in the modeling of qubits, a detailed understanding of the impact of interfacial disorder on the atomic scale is still missing. Within this work, we model realistic Si-based 3D interface structures by ab initio calculations. We improve current modeling approaches by considering a disordered atomistic environment and extract important qubit parameters like valley and spin splittings from these models.