Electromagnetic control of valley splitting in ideal and disordered Si quantum dots

TL;DR

This study models how electric and magnetic fields, along with interface disorder, influence valley splitting in silicon quantum dots, providing insights for optimizing qubit stability.

Contribution

It offers a detailed theoretical analysis of valley splitting dependence on fields and disorder, including the effects of interface steps and magnetic fields.

Findings

Magnetic fields slightly increase valley splitting in ideal interfaces.

Interface steps can significantly reduce valley splitting.

Magnetic fields can either increase or suppress valley splitting depending on disorder configuration.

Abstract

In silicon spin qubits, the valley splitting must be tuned far away from the qubit Zeeman splitting to prevent fast qubit relaxation. In this work, we study in detail how the valley splitting depends on the electric and magnetic fields as well as the quantum dot geometry for both ideal and disordered Si/SiGe interfaces. We theoretically model a realistic electrostatically defined quantum dot and find the exact ground and excited states for the out-of-plane electron motion. This enables us to find the electron envelope function and its dependence on the electric and magnetic fields. For a quantum dot with an ideal interface, the slight cyclotron motion of electrons driven by an in-plane magnetic field slightly increases the valley splitting. Importantly, our modeling makes it possible to analyze the effect of arbitrary configurations of interface disorders. In agreement with previous studies, we show that interface steps can significantly reduce the valley splitting. Interestingly, depending on where the interface steps are located, the magnetic field can increase or further suppress the valley splitting. Moreover, the valley splitting can scale linearly or, in the presence of interface steps, non-linearly with the electric field.