Atomic fluctuations lifting the energy degeneracy in Si/SiGe quantum dots

TL;DR

This paper investigates how atomic-level fluctuations in Si/SiGe quantum dots influence valley splitting, proposing a novel approach to enhance qubit uniformity by manipulating alloy composition fluctuations.

Contribution

It combines 3D atomic-level modeling, theory, and transport data to explain valley splitting variability and suggests a new method to increase valley splitting through alloy composition control.

Findings

Atomic fluctuations explain valley splitting variability.

Incorporating Ge atoms can statistically enhance valley splitting.

The approach offers a pathway to improve qubit uniformity.

Abstract

Electron spins in Si/SiGe quantum wells suffer from nearly degenerate conduction band valleys, which compete with the spin degree of freedom in the formation of qubits. Despite attempts to enhance the valley energy splitting deterministically, by engineering a sharp interface, valley splitting fluctuations remain a serious problem for qubit uniformity, needed to scale up to large quantum processors. Here, we elucidate and statistically predict the valley splitting by the holistic integration of 3D atomic-level properties, theory and transport. We find that the concentration fluctuations of Si and Ge atoms within the 3D landscape of Si/SiGe interfaces can explain the observed large spread of valley splitting from measurements on many quantum dot devices. Against the prevailing belief, we propose to boost these random alloy composition fluctuations by incorporating Ge atoms in the Si quantum well to statistically enhance valley splitting.