Engineered valley-orbit splittings in quantum confined nanostructures in silicon

TL;DR

This paper investigates how to engineer valley-orbit splittings in silicon nanostructures, combining experimental measurements and large-scale atomistic calculations to optimize qubit performance.

Contribution

It provides a comprehensive analysis of valley-orbit splitting in silicon quantum devices using both experimental data and atomistic simulations, revealing how to control this property.

Findings

VO splitting varies with quantum confinement and electric fields.

Large-scale atomistic calculations match experimental results.

Engineered VO gaps can improve silicon qubit stability.

Abstract

An important challenge in silicon quantum electronics in the few electron regime is the potentially small energy gap between the ground and excited orbital states in 3D quantum confined nanostructures due to the multiple valley degeneracies of the conduction band present in silicon. Understanding the "valley-orbit" (VO) gap is essential for silicon qubits, as a large VO gap prevents leakage of the qubit states into a higher dimensional Hilbert space. The VO gap varies considerably depending on quantum confinement, and can be engineered by external electric fields. In this work we investigate VO splitting experimentally and theoretically in a range of confinement regimes. We report measurements of the VO splitting in silicon quantum dot and donor devices through excited state transport spectroscopy. These results are underpinned by large-scale atomistic tight-binding calculations involving over 1 million atoms to compute VO splittings as functions of electric fields, donor depths, and surface disorder. The results provide a comprehensive picture of the range of VO splittings that can be achieved through quantum engineering.