Anisotropic spin-valley coupling in SiMOS and Si/SiGe quantum dots

TL;DR

This study measures and models the anisotropic spin-valley coupling in silicon quantum dots, revealing significant differences between SiMOS and Si/SiGe systems and suggesting ways to optimize qubit performance.

Contribution

It provides a detailed physical model of intra- and inter-valley spin-orbit interactions in silicon quantum dots, comparing two common material platforms.

Findings

SiMOS quantum dots exhibit an order of magnitude larger spin-valley coupling than Si/SiGe.

Angular dependence of spin-valley coupling is similar in both systems, with specific magnetic field orientations minimizing coupling.

The model accurately infers SOC physics from experimental data, aiding qubit optimization.

Abstract

While bulk silicon has long been understood to exhibit relatively weak spin-orbit coupling (SOC), confinement of electrons to quantum dots (QDs) at a silicon heterointerface results in significantly larger SOC. This is a concern for electron spin qubit performance, as intravalley and intervalley SOC can significantly perturb the operation of electron spin qubits. While these interactions can be harnessed to drive coherent rotations in a singlet-triplet qubit, coupling to low-lying excited valley states can lead to undesirable spin relaxation when valley splitting is on resonance with the Zeeman energy. In this work, we measure the angular dependence of the interfacial spin-orbit interaction as a function of the direction and magnitude of an applied external magnetic field in SiMOS and Si/SiGe heterostructures, two common material platforms for silicon spin qubits. We construct a physical model that accurately infers intra- and inter-valley SOC physics from fits to the data, allowing for a direct comparison between these two material systems. For the devices measured we find that, while the $g$-factor differences are comparable, the SiMOS QDs exhibit an order of magnitude larger spin-valley coupling than for Si/SiGe. Moreover, we find that the angular dependence of the spin-valley coupling is similar for both devices, with similar magnetic field orientations minimizing the spin-valley coupling. Our work points towards operational schemes for optimizing spin-valley coupling to avoid or exploit this mechanism for qubit operation.