Controlling spin-orbit interactions in silicon quantum dots using magnetic field direction

TL;DR

This paper investigates how the spin-orbit interaction in silicon quantum dots can be controlled via magnetic field orientation, revealing its impact on qubit coherence and providing pathways for scalable silicon quantum computing.

Contribution

It provides a detailed experimental profile of spin-orbit interactions in silicon quantum dots and demonstrates how magnetic field direction can tune these interactions to improve qubit performance.

Findings

Spin-orbit interactions are dominated by vector potential effects.

Momentum-term spin-orbit interactions vary from 1.85 MHz to 27.5 MHz.

Tuning spin-orbit interaction increases qubit coherence time by 80%.

Abstract

Silicon quantum dots are considered an excellent platform for spin qubits, partly due to their weak spin-orbit interaction. However, the sharp interfaces in the heterostructures induce a small but significant spin-orbit interaction which degrade the performance of the qubits or, when understood and controlled, could be used as a powerful resource. To understand how to control this interaction we build a detailed profile of the spin-orbit interaction of a silicon metal-oxide-semiconductor double quantum dot system. We probe the derivative of the Stark shift, $g$-factor and $g$-factor difference for two single-electron quantum dot qubits as a function of external magnetic field and find that they are dominated by spin-orbit interactions originating from the vector potential, consistent with recent theoretical predictions. Conversely, by populating the double dot with two electrons we probe the mixing of singlet and spin-polarized triplet states during electron tunneling, which we conclude is dominated by momentum-term spin-orbit interactions that varies from 1.85 MHz up to 27.5 MHz depending on the magnetic field orientation. Finally, we exploit the tunability of the derivative of the Stark shift of one of the dots to reduce its sensitivity to electric noise and observe an 80 % increase in $T_2^*$. We conclude that the tuning of the spin-orbit interaction will be crucial for scalable quantum computing in silicon and that the optimal setting will depend on the exact mode of qubit operations used.