  Sensors play a crucial role in advanced apparatuses and it is persistently
pursued to improve their sensitivities. Recently, the singularity of a
non-Hermitian system, known as the exceptional point (EP), has drawn much
attention for this goal. Response of the eigenfrequency shift to a perturbation
$\epsilon$ follows the $\epsilon^{1/n}$-dependence at an $n$th-order EP,
leading to significantly enhanced sensitivity via a high-order EP. However, due
to the requirement of increasingly complicated systems, great difficulties will
occur along the path of increasing the EP order to enhance the sensitivity.
Here we report that by utilizing the spectral anomaly of the coherent perfect
absorption (CPA), the sensitivity at a third-order EP can be further enhanced
owing to the cooperative effects of both CPA and EP. We realize this
synthetically enhanced sensor using a pseudo-Hermitian cavity magnonic system
composed of two yttrium iron garnet spheres and a microwave cavity. The
detectable minimum change of the magnetic field reaches $4.2\times10^{-21}$T.
It opens a new avenue to design novel sensors using hybrid non-Hermitian
quantum systems.

Quantum Physics