Enhanced Magnon-Magnon Entanglement in the Vicinity of Angular Momentum Compensation Point of a Ferrimagnet in a Cavity

Highly entangled states are the key to the realization of quantum information processing. We theoretically investigate magnon-magnon entanglement in a compensated ferrimagnet. We show that the steady-state magnon-magnon entanglement largely enhances in the vicinity of angular momentum compensation point (T_A) when magnons are coupled with photons in a cavity. The origin of this enhancement is that the ground state of ferrimagnet can be close to the Einstein-Podolsky-Rosen state near T_A. This feature is unique to ferrimagnets with different Landé-g factors between sublattices and makes the magnon entanglement of ferrimagnets higher than that of ferromagnets and antiferromagnets.