Anisotropy reduction and tunability of hole-spin qubit g-factor in strained parabolic Ge/SiGe quantum wells

TL;DR

This paper investigates how the confinement profile in Ge/SiGe quantum wells influences the g-factor anisotropy of hole-spin qubits, demonstrating that parabolic wells offer greater tunability and potential for improved qubit performance.

Contribution

It provides analytical and numerical analysis comparing square and parabolic quantum wells, highlighting the advantages of parabolic wells for g-factor tunability.

Findings

Decreasing in-plane confinement length reduces g-factor anisotropy.

Parabolic wells offer broader g-factor tunability than square wells.

Engineering quantum well profiles can optimize qubit properties.

Abstract

Hole-spin qubits in planar Ge/SiGe heterostructures have attracted significant attention in recent years owing to their favorable electrical characteristics and prolonged coherence times. However, the strong spin-orbit interaction also makes them susceptible to charge noise and inhomogeneous strain. This is further exacerbated by the highly anisotropic g-factor of the planar design. Although there are some known strategies to suppress charge noise, one approach is to engineer an isotropic g-factor. In this work we analyze how qubit confinement profile affects the g-factor of hole-spin qubits. We show that decreasing the characteristic in-plane qubit confinement length reduces the g-factor anisotropy. We perform analytical and numerical analysis to compare two types of quantum wells: square wells and parabolic wells. We show that square wells have limited tunability, while parabolic wells offer broader tunability, making them more promising for qubit engineering.