Strong photon coupling to high-frequency antiferromagnetic magnons via topological surface states

TL;DR

This paper demonstrates strong, controllable coupling between antiferromagnetic magnons and microwave photons via topological surface states, leveraging electric dipole interactions and squeezing effects to enhance coupling strength for quantum technologies.

Contribution

It introduces a novel mechanism for strong magnon-photon coupling using topological insulator surface states and squeezing, surpassing previous limitations of direct coupling methods.

Findings

Achieved coupling strength up to several orders stronger than direct magnon-photon coupling.

Identified electric dipole coupling mediated by topological surface states.

Demonstrated potential for high-frequency cavity magnonics in quantum information applications.

Abstract

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 insulator (AFM) interfaced with a topological insulator (TI), taking Bi$_2$Se$_3$--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.