Directional emission of a broadband squeezed microwave field

Broadband squeezed light is a valuable resource in the quantum information science community. Here, we propose an appealing method for the directional generation of broadband microwave squeezing based on hybrid magnonics, where multiple chiral cavity-magnonic subsystems are connected together through a bidirectional waveguide in a cascading way. The chirality arises from the selective coupling between the Kittel mode in the ferrimagnetic yttrium iron garnet sphere and one of the two degenerate counter-rotating microwave modes in a ring-shaped cavity. By introducing Floquet engineering to simultaneously induce red and blue sidebands in the photon-magnon coupling, the chiral squeezing-type interaction can be engineered in each cavity-magnonic subsystem. Considering all the photon-magnon couplings in the cascaded system with the same chirality, we show that a broadband squeezed microwave field can be emitted on demand to either of the two output ports along the waveguide. Compared with a single chiral cavity-magnonic system, both the squeezing amount and the bandwidth can be significantly enhanced through the cumulative effect of the cascaded system.