Strong Coupling between Propagating Spin Waves and Microwave Photons in a Superconducting Resonator.

We demonstrate strong coupling between propagating spin-wave modes and microwave photons in superconducting resonator-magnetic thin film hybrid circuits. By fabricating the resonator directly on yttrium iron garnet thin films grown on rare-earth-free Y_{3}Sc_{2}Ga_{3}O_{12} substrates, we achieve strong coupling of both Damon-Eshbach and backward-volume spin-wave modes to the resonator, with coupling strengths exceeding both the magnon and photon damping rates. Furthermore, we observe nonreciprocal spin-wave radiation of the hybrid magnonic mode in the Damon-Eshbach configuration, highlighting the potential for incorporating intrinsic spin-wave nonreciprocity into hybrid magnonic systems. These results open new avenues for integrating spin-wave magnonics with cavity magnonics and for harnessing spin waves for potential applications in quantum information science.