Spin-orbit Interactions for Singlet-Triplet Qubits in Silicon

TL;DR

This paper investigates spin-orbit interactions in silicon quantum dot qubits, revealing multiple mechanisms influenced by crystal symmetry and tunneling, which are crucial for improving qubit control and coherence.

Contribution

It provides experimental evidence of intravalley, intervalley, and tunneling spin-flip mechanisms in silicon singlet-triplet qubits, enhancing understanding of spin-orbit effects.

Findings

Identified intravalley and intervalley mechanisms dominant at different magnetic field orientations.

Observed a third spin-flip mechanism due to tunneling between quantum dots.

Results align with a broken crystal symmetry model.

Abstract

Spin-orbit coupling is relatively weak for electrons in bulk silicon, but enhanced interactions are reported in nanostructures such as the quantum dots used for spin qubits. These interactions have been attributed to various dissimilar interface effects, including disorder or broken crystal symmetries. In this Letter, we use a double-quantum-dot qubit to probe these interactions by comparing the spins of separated singlet-triplet electron pairs. We observe both intravalley and intervalley mechanisms, each dominant for [110] and [100] magnetic field orientations, respectively, that are consistent with a broken crystal symmetry model. We also observe a third spin-flip mechanism caused by tunneling between the quantum dots. This improved understanding is important for qubit uniformity, spin control and decoherence, and two-qubit gates.