Terahertz Magnon-Polariton Control Using a Tunable Liquid Crystal Cavity.

Strong coupling of light to a collective spin excitation in antiferromagnets gives rise to hybrid modes called magnon-polaritons. They are highly promising for data manipulation and transfer at terahertz rates, much faster than in the case of ferromagnetic magnon-polaritons, which operate at GHz frequencies. Yet, control of terahertz magnon-polaritons by the voltage, i.e., without ohmic dissipation losses, remains challenging. Here, we showcase the ability to remotely control antiferromagnetic magnon-polaritons at room temperature using an electric field by integrating a highly birefringent liquid crystal layer into a terahertz Fabry-Perot cavity containing an antiferromagnetic crystal. Positioned several millimeters from the magnetic material, the liquid crystal allows for electrical manipulation of the cavity's photonic environment by control of its dielectric constant. This adjustment, in turn, influences the extent of magnon dressing by cavity photons, thereby controlling the vacuum Rabi oscillations of the magnon resonance coupled to a particular cavity mode. Our approach enables reversible tuning of magnon-photon hybridization that can be triggered without direct electrical contact or alteration of the magnetic medium. These findings pave the way for voltage-programmable terahertz magnonic devices and open new avenues for noninvasive control strategies in spin-based information processing technologies.