Coupling conduction-band valleys in SiGe heterostructures via shear strain and Ge concentration oscillations

TL;DR

This paper proposes a novel method to enhance conduction-band valley coupling in SiGe heterostructures using shear strain and Ge concentration oscillations, enabling scalable quantum computing with more practical fabrication techniques.

Contribution

It introduces a second-order coupling mechanism via shear strain that mimics short-wavelength oscillations in long-wavelength structures, simplifying fabrication.

Findings

Shear strain induces Brillouin-zone folding enhancing valley coupling.

Long-wavelength Ge oscillations can replicate effects of short-wavelength oscillations.

Strain can be achieved through standard fabrication techniques.

Abstract

Engineering conduction-band valley couplings is a key challenge for Si-based spin qubits. Recent work has shown that the most reliable method for enhancing valley couplings entails adding Ge concentration oscillations to the quantum well. However, ultrashort oscillation periods are difficult to grow, while long oscillation periods do not provide useful improvements. Here, we show that the main benefits of short-wavelength oscillations can be achieved in long-wavelength structures through a second-order coupling process involving Brillouin-zone folding induced by shear strain. We finally show that such strain can be achieved through common fabrication techniques, making this an exceptionally promising system for scalable quantum computing.