Multimode cavity magnonics in mumax+: from coherent to dissipative coupling in ferromagnets and antiferromagnets

TL;DR

This paper introduces a GPU-accelerated extension for mumax+ that simulates cavity magnonics, enabling detailed modeling of photon-magnon interactions, including dissipative effects, with validated benchmarks across various coupling regimes.

Contribution

The authors develop a two-tier cavity magnonics extension for mumax+ that integrates cavity modes directly into micromagnetic simulations, allowing efficient and detailed modeling of complex photon-magnon interactions.

Findings

Validated with eight benchmark simulations.

Demonstrated transition from level repulsion to attraction.

Enabled selective mode addressing and hybridization analysis.

Abstract

Coherent coupling between microwave cavity photons and magnon excitations enables quantum transduction, magnon-mediated entanglement, and magnon number-resolved detection. Micromagnetic simulation of photon-magnon coupling typically requires either modifying the core solver or implementing a full electromagnetic solver. Here we present a two-tier cavity magnonics extension for mumax+, a GPU-accelerated open-source micromagnetic framework. The first tier consists of CUDA kernels that integrate N cavity-mode ODEs simultaneously with the LLG equation inside the GPU-based RK45 adaptive time-stepper, eliminating per-step GPU-CPU transfers; spatially resolved mode profiles enter both the coupling and the feedback, enabling selective addressing of non-uniform spin-wave modes. The second tier is a lightweight Python co-simulation class that reproduces the same uniform-mode physics through operator-split RK4 integration without recompilation. We validate the implementation with eight benchmark simulations: (i) magnon-polariton anticrossing spectra, (ii) vacuum Rabi oscillations, (iii) the cooperativity phase diagram spanning weak-to-strong coupling regimes, (iv) cavity mode-profile-dependent coupling selection rules, (v) multi-mode polariton hybridization with magnon-mediated cavity-cavity energy transfer, (vi) mode-selective coupling via spatial overlap engineering, (vii) antiferromagnetic magnon-cavity coupling with Neel-vector spectroscopy, and (viii) abnormal anticrossing from dissipative photon-magnon coupling, demonstrating the transition from level repulsion to level attraction.