Strong coupling between magnons and Anderson-localized microwave photons

Abstract

Anderson localization turns disorder into mirror-free wave confinement. When such localized modes couple strongly to a tunable collective excitation, the disorder landscape can become a resource for light–matter control. Here, we demonstrate strong coupling between the Kittel magnon of a yttrium iron garnet sphere and Anderson-localized microwave photons in a one-dimensional split-ring-resonator lattice. The experiment progresses from an ordered lattice, where a movable magnon maps extended standing-wave amplitudes, to a single-defect lattice with enhanced local coupling, and finally to a disordered lattice hosting multiple localized modes. In the disordered device, a localized microwave mode exhibits a resolved 94 MHz avoided crossing, corresponding to g/2π = 47 MHz. Translating the YIG sphere reconstructs the spatial coupling landscape and shows that the coupling follows the local photonic wave function amplitude. These results establish magnon spectroscopy as a site-resolved probe of disordered microwave eigenstates and point toward programmable disorder for reconfigurable magnon–photon interfaces.