  Quantum computing hardware has received world-wide attention and made
considerable progress recently. YIG thin film have spin wave (magnon) modes
with low dissipation and reliable control for quantum information processing.
However, the coherent coupling between a quantum device and YIG thin film has
yet been demonstrated. Here, we propose a scheme to achieve strong coupling
between superconducting flux qubits and magnon modes in YIG thin film. Unlike
the direct $\sqrt{N}$ enhancement factor in coupling to the Kittel mode or
other spin ensembles, with N the total number of spins, an additional spatial
dependent phase factor needs to be considered when the qubits are magnetically
coupled with the magnon modes of finite wavelength. To avoid undesirable
cancelation of coupling caused by the symmetrical boundary condition, a CoFeB
thin layer is added to one side of the YIG thin film to break the symmetry. Our
numerical simulation demonstrates avoided crossing and coherent transfer of
quantum information between the flux qubits and the standing spin waves in YIG
thin films. We show that the YIG thin film can be used as a tunable switch
between two flux qubits, which have modified shape with small direct inductive
coupling between them. Our results manifest that it is possible to couple flux
qubits while suppressing undesirable cross-talk.
