Phase‐Modulated Steady‐State Multipartite Entanglement Realized by Two Microwave Parametric Amplifiers

Abstract It is proposed that how to generate and amplify multipartite entanglement simply by applying two microwave parametric amplifiers (MPAs) in a cascaded system without parametric downconversion interactions. Both the bipartite and tripartite entanglement of the three‐mode bosonic system are induced via the nonlinear gain of the two MPAs, which does not require strong coherent parametric coupling. Simultaneously, the intrinsic dissipation and detuning of the quadrature modes are corrected by modulating the phase difference of the MPAs, which directly changes the photon statistical distribution of the microwave cavity, so that both bipartite and tripartite entanglement of the dual‐cavity‐magnon system can be significantly enhanced. In particular, the phase‐modulated (PM) tripartite entanglement reaches the degree of 0.1 and breaks the limit of weak tripartite entanglement (on the degree of 0.01 and 0.001), which is a milestone breakthrough. More importantly, the PM multipartite entanglement is axisymmetric or centrosymmetric with respect to detuning and phase difference, which provides a bidirectional parameter selection for the experimental preparation of strong steady‐state entanglement. Furthermore, the PM multipartite entanglement is accompanied by improved robustness against the thermal bath temperature. The phase modulation mechanism can be potentially applied to construct stable multipartite entanglement networks and quantum information processing.