Controllable valley splitting in silicon quantum devices

TL;DR

This paper demonstrates that lateral confinement in silicon quantum devices can significantly enhance valley splitting, which is crucial for stable spin qubits, by controlling atomic-scale interface steps and magnetic confinement.

Contribution

It reveals that lateral confinement and magnetic fields can be used to controllably increase valley splitting in silicon quantum dots, addressing a key decoherence issue.

Findings

Valley splitting up to 1.5 meV achieved.

Lateral confinement limits electron wavefunctions to atomic steps.

Valley splitting can be controlled over a wide range.

Abstract

Silicon has many attractive properties for quantum computing, and the quantum dot architecture is appealing because of its controllability and scalability. However, the multiple valleys in the silicon conduction band are potentially a serious source of decoherence for spin-based quantum dot qubits. Only when these valleys are split by a large energy does one obtain well-defined and long-lived spin states appropriate for quantum computing. Here we show that the small valley splittings observed in previous experiments on Si/SiGe heterostructures result from atomic steps at the quantum well interface. Lateral confinement in a quantum point contact limits the electron wavefunctions to several steps, and enhances the valley splitting substantially, up to 1.5 meV. The combination of electronic and magnetic confinement produces a valley splitting larger than the spin splitting, which is controllable over a wide range. These results improve the outlook for realizing spin qubits with long coherence times in silicon-based devices.