We show strong coupling between antiferromagnetic magnons and microwave cavity photons at both high and externally controllable magnon frequencies. Using the fully quantum mechanical path-integral method, we study an antiferromagnetic (AFM) insulator interfaced with a topological insulator (TI), taking ${\mathrm{Bi}}_2{\mathrm{Se}}_3\text{−}\mathrm{MnSe}$ as a representative example. We show that the mutual coupling of the spin-polarized surface states of the TI to both the squeezed magnons and the circularly polarized cavity photons results in a Chern-Simons term that activates the stronger electric, rather than magnetic, dipole coupling. Moreover, a squeezing-mediated enhancement of the coupling is achieved due to the unequal interfacial exchange coupling to the AFM sublattices, resulting in a coupling strength up to several orders stronger than for direct magnon-photon coupling. While direct cavity-AFM coupling has so far been limited in its applicability due to weak or low frequency coupling, this result may advance the utilization of high-frequency cavity magnonics and enable its incorporation into quantum information technology.

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• Cavity quantum electrodynamics
• Light-matter interaction
• Magnons
• Polaritons
• Strong interaction
• Antiferromagnets
• Topological materials
• Cavity methods
• Path-integral methods