Coherent coupling between ferromagnetic magnon and superconducting qubit

Coherent coupling between paramagnetic spin ensembles and superconducting quantum circuits is now widely studied for quantum memories and microwave-to-optical quantum transducers. Since those applications require strong coupling and sufficiently long coherence time simultaneously, collective excitation (magnon) in yttrium iron garnet (YIG), a typical ferromagnetic insulator, is an alternative promising candidate. The material is known to have a high spin density and a narrow ferromagnetic-resonance (FMR) linewidth. Recently, we achieved strong coupling between a 3D microwave cavity and the uniformly precessing spin mode. In this talk, we step forward to the control and measurement of magnons using superconducting circuits. We demonstrate coherent coupling between a magnon excitation in a millimeter-sized ferromagnetic sphere and a superconducting qubit, in which the interaction is mediated by a microwave cavity. We observe the coupling strength exceeding the damping rates, revealing that the system is in the strong coupling regime. Furthermore, we study a tunable coupling scheme using a microwave drive and the time-domain control of magnons. Our approach provides a versatile tool for control and measurement of the magnon excitations in the quantum regime.