Enhanced magnon-magnon entanglement in the vicinity of an 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 Lande g factors between sublattices and makes the magnon entanglement of ferrimagnets higher than that of ferromagnets and antiferromagnets. Our result will invigorate research on quantum information processing based on magnon-magnon entanglement.