Strong on-Chip Microwave Photon-Magnon Coupling Using Ultralow-Damping Epitaxial Y₃Fe₅O₁₂ Films at 2 K

Y3Fe5O12 is arguablythe bestmagnetic material for magnonic quantum information science (QIS) becauseof its extremely low damping. We report ultralow damping at 2 K inepitaxial Y3Fe5O12 thin films grownon a diamagnetic Y3Sc2Ga3O12 substrate that contains no rare-earth elements. Using these ultralowdamping YIG films, we demonstrate for the first time strong couplingbetween magnons in patterned YIG thin films and microwave photonsin a superconducting Nb resonator. This result paves the road towardscalable hybrid quantum systems that integrate superconducting microwaveresonators, YIG film magnon conduits, and superconducting qubits intoon-chip QIS devices.