Kerr nonlinearity regulated nonreciprocal amplification in cavity magnon polaritons.

We propose a three-mode cavity magnonic system consisting of one magnon mode and two cavity photon modes to achieve nonreciprocal transmission and obtain analytical conditions for nonreciprocal amplification. In such a cavity-magnon system, the direction of nonreciprocal amplification can be modulated by the transition phase between two coupled cavity photon modes; meanwhile, strong magnon Kerr nonlinearity leads to a transition from nonreciprocal amplification to bidirectional attenuation. Moreover, we reveal the mechanism for the nonreciprocal amplification by non-Hermitian spectrum and find that the maximum amplification transmission coefficient can be controlled by the eigenvalues of the effective Hamiltonian. Our results provide an opportunity for engineering various nonreciprocal devices such as photonic circulators, isolators, and amplifiers.