Quantum magnon conversion accompanying magnon antibunching

The implementation of quantum network made up of multiple nodes and channels needs to take advantage of hybrid quantum systems. So far, in the hybrid ferromagnet-superconductor quantum system, the establishment of the remote effective interactions based on the virtual photons exchange mediated by the microwave cavity mode has been experimentally confirmed, providing a physical basis for the implementation of the remote signal transfer from one node to another. In this work, we put forward a magnon-based hybrid quantum system consisting of two macroscopic spin subsystems [i.e., millimeter-diameter ferromagnetic yttrium-iron-garnet (YIG) spheres] and one transmon-type superconducting qubit, and show that the mechanism of the cavity-mediated remote magnon-mode intertalk is feasible for achieving microwave signal transfer, simultaneously accompanied by a transition from Poissonian to sub-Poissonian statistics. We find that by tuning the typical system parameters properly, even if there is a mismatch in magnon-mode frequencies or dissipation rates between the two YIG spheres, the microwave information transfer from one YIG sphere to another is still robust, where the signal output through another YIG sphere exhibits pronounced antibunching. In addition, the proposed hybrid quantum system possesses a robustness window against the dissipation rates of both the qubit and the two Kittel modes. The analytical calculations and numerical simulations are conducted under experimentally accessible conditions, and the consistency of the results attained by these two methods makes our research more credible. Physically, we notice that two conversion channels are opened. One channel comes from the linear coupling. The other is based on the nonlinear interaction, which also is the underlying mechanism responsible for nonclassical sub-Poissonian signal output.