Electrically Tuneable Variability in Germanium Hole Spin Qubits

TL;DR

This paper introduces a method to electrically control and reduce variability in germanium hole spin qubits, enhancing their suitability for scalable quantum computing by engineering the g-tensor response.

Contribution

It presents a systematic approach to engineer the spin qubit response via quantum dot asymmetry, enabling on-demand electric g-tensor control and variability suppression.

Findings

Electrical tuning of the g-tensor is achieved through quantum dot size and asymmetry.

Variability in spin response can be significantly reduced for specific magnetic field directions.

Unstrained germanium channels are optimal for g-tensor engineering.

Abstract

Hole spin qubits in planar germanium heterostructures are frontrunners for scalable semiconductor quantum computing. However, their current performance is mostly limited by large dot-to-dot variability that leads to uncontrolled qubit energies and random tilts in the spin quantization axis. Here, we propose a systematic and local method to engineer the spin qubit response by imprinting a controlled anisotropy in the quantum dot confinement, enabling on-demand electric g-tensor control. In particular, we find that both the quantum-dot size and asymmetry allow electrical tuning of the g-tensor and significantly suppress magnitude and angular variability of the spin response for selected magnetic field directions. We confirm this behavior by analyzing single-disorder realizations and statistical ensembles in state-of-the-art strained and unstrained germanium channels, showing that the latter provides an optimal path for $g$-tensor engineering. Our results provide practical design principles for on-demand control of the spin response and mitigating variability, paving the way towards large-scale germanium-based quantum computers.