Disentangling orbital and confinement contributions to $g$-factor in Ge/SiGe hole quantum dots

TL;DR

This study disentangles the orbital and confinement effects on the hole $g$-factor in Ge/SiGe quantum dots, revealing gate-tunability and clarifying previous measurement discrepancies crucial for qubit control.

Contribution

It introduces a method to distinguish pure Zeeman and orbital contributions to the $g$-factor in hole quantum dots, enhancing understanding of spin-orbit effects in qubit systems.

Findings

Orbital and Zeeman contributions to $g$-factor are distinguishable using excitation spectra.

Gate-tuning of $g$-factors by 15% demonstrates control over qubit properties.

Discrepancies between different measurement methods are clarified by separating orbital effects.

Abstract

Spin qubits are typically operated in the lowest orbital of a quantum dot to minimize interference from nearby states. In valence-band hole systems, strong spin-orbit coupling links spin and orbital degrees of freedom, strongly influencing the hole $g$-factor, a key parameter for qubit control. We investigate the out-of-plane $g$-factor in Ge quantum dots using excitation (single-particle) and addition (many-body) spectra. Excitation spectra allow us to distinguish the pure Zeeman $g$-factor from orbital contributions to the magnetic field splitting of states despite the strong spin-orbit coupling. This distinction clarifies discrepancies between $g$-factors extracted with the two methods, for different orbital states and different hole numbers. Furthermore, we find gate-tunability of $g$-factors at the level of 15%, highlighting its relevance for all-electric qubit manipulation.