Nanoscale Stray Fields from Micromagnets for Optimal Spin Qubit Architecture

Area of Science:

• Quantum computing
• Spintronics
• Materials science

Background:

• On-chip micromagnets are crucial for electrical control of spin qubits in circuit quantum electrodynamics (QED).
• Accurate modeling of micromagnet stray fields, beyond simple approximations, is essential for predicting spin qubit performance.

Purpose of the Study:

• To develop a reliable micromagnetic simulation framework for predicting spin qubit performance.
• To investigate the stray field characteristics of various magnetic materials (Co, Co/Ta, CoFe) in unsaturated regimes.

Main Methods:

• Utilized thin-film characterization of Co, Co/Ta multilayers, and CoFe films.
• Employed nanoscale stray-field measurements using nitrogen-vacancy (NV) center magnetometry.
• Developed and validated a micromagnetic simulation framework accounting for nonuniform magnetization.

Main Results:

• CoFe micromagnets were shown to generate antisymmetric fields exceeding ±100 mT in double quantum-dot geometries.
• The high saturation magnetization and magnetocrystalline anisotropy of CoFe contribute to strong stray fields.
• Predicted spin-photon coupling strength |gs/gc| reached approximately 0.5 for spin qubits coupled to microwave resonators.

Conclusions:

• The established simulation framework enables accurate prediction of micromagnet stray fields for spin qubit control.
• CoFe micromagnets show significant potential for high-fidelity operations in circuit QED architectures.
• This work advances the integration of spin qubits into scalable quantum computing platforms.