Magnetically Tuned Continuous Transition from Weak to Strong Coupling in Terahertz Magnon Polaritons

TL;DR

This paper demonstrates a system where increasing magnetic field causes a continuous transition from weak to strong coupling in terahertz magnon polaritons, enabling in situ control of non-Hermitian systems.

Contribution

It introduces a magnetic field-controlled system that allows real-time monitoring of the weak-to-strong coupling transition in magnon polaritons.

Findings

Observation of Rabi splitting above 14 T magnetic field

Continuous tuning of coupling regime with magnetic field

Identification of an exceptional point in the transition

Abstract

Depending on the relative rates of coupling and dissipation, a light-matter coupled system is either in the weak- or strong-coupling regime. Here, we present a unique system where the coupling rate continuously increases with an externally applied magnetic field while the dissipation rate remains constant, allowing us to monitor a weak-to-strong coupling transition as a function of magnetic field. We observed a Rabi splitting of a terahertz magnon mode in yttrium orthoferrite above a threshold magnetic field of ~14 T. Based on a microscopic theoretical model, we show that with increasing magnetic field the magnons transition into magnon polaritons through an exceptional point, which will open up new opportunities for in situ control of non-Hermitian systems.