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arXiv · 2607.15333

Nanoscale stray fields from micromagnets for optimal spin qubit architecture

Sandrine Lopes·Quentin Schaeverbeke·Matthieu M. Desjardins·Daniel Lacour·Michel Hehn·François Montaigne
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Abstract

On-chip micromagnets generate local magnetic-field asymmetries, enabling electrical control of spin qubits via electric dipole spin resonance and their integration into circuit quantum electrodynamics (QED) architectures. Accurate prediction of spin-qubit performance requires modeling micromagnet stray fields beyond the saturated-magnet approximation, accounting for nonuniform magnetization. Here, we combine thin-film characterization of Co, Co/Ta multilayers, and CoFe films with nanoscale stray-field measurements using NV-center magnetometry in the unsaturated regime to establish a reliable micromagnetic simulation framework. We show that CoFe micromagnets generate antisymmetric fields in double quantum-dot geometries exceeding +/- 100mT, owing to their high saturation magnetization and favorable magnetocrystalline anisotropy. For spin qubits coupled to microwave resonators, the predicted spin-photon coupling reaches $\left| g_s/g_c \right| \approx 0.5$, where $g_c$ denotes the charge-photon coupling strength of the underlying charge qubit, highlighting the potential for high-fidelity operations in circuit QED architectures.

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Sandrine Lopes, Quentin Schaeverbeke, Matthieu M. Desjardins, Daniel Lacour, Michel Hehn, François Montaigne. 2026-07-16. Nanoscale stray fields from micromagnets for optimal spin qubit architecture. https://doi.org/10.1021/acs.nanolett.6c01469

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