Tunable strong coupling between a transmon and a magnon

Coherent coupling between a ferromagnetic magnon and a superconducting qubit demonstrates a special fascination in the quantum information field. Here, we construct a hybrid system to realize tunable strong coupling between a transmon and a magnon. In a hybrid system, the transmon couples to a cavity while the magnon couples to the other cavity. Meanwhile, the two cavities are coupled via a hopping interaction. In addition, we demonstrate some applications of this system to quantum information. Specifically, a high-fidelity $i$swap${}^{†}$ gate and a maximally entangled state between the transmon and the magnon with this coupling system can be realized even if the dissipation is considered. Moreover, by employing more cavities and magnons, the $W$-type entangled state can be created with multiple transmons. This hybrid system provides an alternative platform for scalable quantum information processing.