Magnon blockade in a QED system with a giant spin ensemble and a giant atom coupled to a waveguide

We propose a scheme to achieve the magnon blockade (MB) effect in a system consisting of a giant spin ensemble and a giant atom coupled to a waveguide. We show a physical mechanism for generating the MB through non-Hermitian anharmonicity. The non-Hermitian magnon blockade (NHMB) is realized in braided, nested, and separate coupling configurations. The NHMB is shown to be useful for the preparation of a high-efficiency and high-purity single magnon. Remarkably, the coexistence phenomenon of the conventional magnon blockade and the unconventional magnon blockade occurs and their conversion can be completed in the braided and nested coupling configurations. This result realizes the modulation between efficiency and purity of single-magnon generation. For the separate coupling configuration, the frequency-tunable NHMB is obtained due to the variation of Lamb shifts. The phase caused by the photon propagating between neighboring coupling points offers a simple and flexible method to modulate the conversion of MB effects induced by multiple physical mechanisms. Our results open a pathway to manipulate the generation of the MB on demand, which has potential applications in producing a single-magnon source and performing magnon-based quantum information processing.