Topological mode switch by exceptional point encircling in a cavity magnonic system

Cavity magnonic systems have attracted wide interest for their potential in bridging quantum electrodynamics and magnetism, while non-Hermitian physics has similarly garnered increasing attention. Here, we propose and experimentally investigate a tunable cavity magnonic system comprising a microwave cavity mode coupled to the Kittel mode in an yttrium iron garnet (YIG) ferromagnetic sphere. By controlling the damping and adjusting the cavity photon–magnon coupling strength, we realize and characterize exceptional points (EPs) in this system. We observe a transition in the transmission spectra from anticrossing to crossing as the coupling strength is tuned across the EP threshold, confirming the EP’s presence. Furthermore, by carefully encircling the EP in a parameter space, we demonstrate dynamic topological mode switching, wherein the system’s eigenvalues interchange upon completing a loop around the EP. Our results highlight the flexibility of a cavity magnonic platform for exploring non-Hermitian phenomena and pave the way for EP-based device applications in quantum information processing and topological photonics.