Multistability of quantum entanglement and squeezing in nonlinear cavity magnonic systems

We focus on the multistability of quantum states in a nonlinear cavity magnonic system based on the cooperative effect of the magnon Kerr nonlinearity and the photon Kerr nonlinearity. Under experimentally feasible parameters, we first verify the multistability of magnon frequency shifts induced by the two nonlinearities by solving the classical mean value equations of the system. Then the multistability of the entangled state and squeezed state in the nonlinear system is revealed by investigating the quantum dynamics of the system fluctuations. By comparison, it is found that the multistable parameter regions for the classical states are exactly the same as those for the quantum states. We also explore the role of the system dissipations in the emergence of multistability, and the numerical results show that the multistable parameter regions will progressively shrink with the increase of the dissipations. These findings are meaningful for the study of nonlinear quantum effects in hybrid systems and may have potential applications in quantum information processing, precision measurement, and multifunctional quantum devices.