Strong coupling between spin waves and a microwave photons in a superconducting resonator

Hybrid magnonic systems have recently emerged as a new promising direction that exploits the advantages of magnon excitations for processing quantum information [1]. In particular, propagating spin waves can demonstrate intrinsic nonreciprocity and wavelength matching to optical light. The unique properties ofThus, spin waves make them potential for implementingmay enable on-chip microwave isolators and microwave-to-optic transducers with a major benefit of frequency tunability by magnetic field. In this work, we develop a novel hybrid magnonic system with superconducting resonators directly fabricated on top of yttrium iron garnet (YIG) films to achieve coherent coupling with spatially nonuniform spin waves. The YIG films are grown on Y₃Sc₂Ga₃O₁₂ (YSGG) substrate, which eliminates rare-earth elements compared with the commonly used Gd₃Ga₅O₁₂ (GGG) substrate and thus exhibit zero magnetism at cryogenic temperature [2]. This is crucial for achieving high quality factor for the superconducting resonator fabricated on top. With this new hybrid system, we demonstrate strong coupling between spin waves in the YIG film and photons of the resonator. The small antenna width of the superconducting resonator down to 500 nm allows us to coherently couple to the spatially nonuniform spin wave modes, with a frequency shift from the uniform mode matching well with the width of the antenna and eventually the wavelength of the spin waves. Our results provide a new circuit platform for integrating propagating magnonics with cryogenic superconducting quantum circuits and developing future quantum magnonic functionality with spin wave engineering.