Quantum-enhanced metrology in cavity magnonics

Magnons, as fundamental quasiparticles that emerge in elementary spin excitations, hold a big promise for innovating quantum technologies in information coding and processing. By establishing the exact relation between Fisher information and entanglement in partially accessible metrological schemes, we rigorously prove that bipartite entanglement plays a crucial role during the dynamical encoding process. However, the presence of an entanglement during the measurement process unavoidably reduces the ultimate measurement precision. These findings are verified in an experimentally feasible cavity magnonic system engineered for detecting a weak magnetic field by performing precision measurements through the cavity field. Moreover, we further demonstrate that, within a weak-coupling region, measurement precision can reach the Heisenberg limit. Additionally, quantum criticality also enables us to enhance measurement precision in a strong-coupling region.