Strong magnon-photon coupling on-chip for YIG in the zero-temperature limit*

The integration of spin-wave and superconducting technologies is a promising method for creating novel hybrid devices for future information processing technologies to store, manipulate, or convert data in both classical and quantum regimes. While hybrid magnon-polariton systems have been studied using bulk yttrium iron garnet (Y₃Fe₅O₁₂, YIG) and photon cavities, the incompatibility of YIG growth techniques with CMOS technologies impedes the creation of high-quality factor magnon-polariton systems on-chip with superconducting quantum technologies. To overcome this impediment, we have used Plasma Focused Ion Beam (PFIB) technology to integrate YIG on-chip with superconducting microwave devices, taking advantage of precision placement down to the micron-scale. Ferromagnetic resonance has been measured at millikelvin temperatures on PFIB-processed YIG samples using planar microwave circuits. Furthermore, we demonstrate strong coupling between superconducting resonator and YIG ferromagnetic resonance modes. This achievement of strong coupling on-chip is a crucial step toward fabrication of functional hybrid quantum devices that advantage from spin-wave and superconducting components.