Coherent coupling between a ferromagnetic magnon and a superconducting qubit

TLDR

In condensed matter, ordered phases support collective excitations that extend over macroscopic scales, with magnons being the quantum excitations of spin systems. The study demonstrates coherent coupling between a single magnon in a millimeter‑sized ferromagnetic sphere and a superconducting qubit via virtual photons in a microwave cavity. The coupling is achieved through virtual photon mediation in a microwave cavity, and a parametric drive enables tunable magnon‑qubit interaction. The achieved coupling strength surpasses damping rates, placing the system in the strong‑coupling regime and offering a versatile tool for quantum control of magnons that could advance quantum information processing.

Abstract

Rigidity of an ordered phase in condensed matter results in collective excitation modes spatially extending to macroscopic dimensions. A magnon is a quantum of such collective excitation modes in ordered spin systems. Here, we demonstrate the coherent coupling between a single-magnon excitation in a millimeter-sized ferromagnetic sphere and a superconducting qubit, with the interaction mediated by the virtual photon excitation in a microwave cavity. We obtain the coupling strength far exceeding the damping rates, thus bringing the hybrid system into the strong coupling regime. Furthermore, we use a parametric drive to realize a tunable magnon-qubit coupling scheme. Our approach provides a versatile tool for quantum control and measurement of the magnon excitations and may lead to advances in quantum information processing.