Programmable cavity magnonics via the Goldstone mode of bilayer cuprate antiferromagnets

Abstract

Hybrid platforms that couple microwave photons to collective spin excitations offer promising routes for coherent information processing, yet conventional magnets face inherent trade-offs among coupling strength, coherence, and tunability. We demonstrate that bilayer cuprate antiferromagnets—exemplified by YBa2Cu3O6+x—provide an alternative approach enabled by their unique magnon spectrum. Using a neutron-constrained bilayer spin model, we obtain the complete Γ-point spectrum and identify an in-plane acoustic α mode that remains gapless and Zeeman linear, alongside an in-plane optical β mode stabilized by weak anisotropy whose frequency can be tuned from GHz to THz ranges. When coupled to a single-mode microwave cavity, these modes create two distinct channels with a magnetically tunable α-photon coupling where |Gα|∝B−1/2 and a nearly field-independent β0photon coupling. This asymmetric behavior enables continuous, single-parameter control spanning from dispersive to strong coupling regimes. In the dispersive limit, Schrieffer-Wolff analysis reveals cavity-mediated magnon-magnon coupling gαβeff∝gαgβ/(ωm−ωc), while near triple resonance (fc=fα=fβ) the normal modes reorganize into bright and dark superpositions governed by a single collective energy scale. The calculated transmission exhibits vacuum Rabi splittings, dispersive shifts, and Fano-like lineshapes that provide concrete experimental benchmarks and suggest the potential for programmable filtering and coherent state transfer across the GHz-THz frequency range if realized experimentally with suitable interfaces.

Source-reported materials — not catalogue approval

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