Enhancement of signal-to-noise ratio at a high-order exceptional point of coherent perfect absorption

TL;DR

This paper demonstrates a twelve-fold enhancement in signal-to-noise ratio for magnetic field sensing using a third-order exceptional point in a non-Hermitian magnonic system, overcoming noise divergence issues.

Contribution

The study introduces a novel passive magnonic platform utilizing a third-order CPA exceptional point to significantly improve SNR and responsivity in sensing applications.

Findings

Achieved twelve-fold SNR enhancement at CPA EP3

Realized seventyfold SNR and 400-fold responsivity improvements

Confirmed noise suppression through extensive measurements

Abstract

Exceptional points (EPs) in non-Hermitian systems offer a remarkably strong response to weak perturbations, but the nonorthogonal nature of the corresponding eigenvectors causes noise to diverge, hindering EPs practical application. Here, we report a twelve-fold enhancement of signal-to-noise ratio (SNR) in magnetic field sensing enabled by a third-order EP of coherent perfect absorption (CPA EP3) in a passive cavity magnonic system. This non-Hermitian magnonic platform comprises two identical yttrium iron garnet (YIG) spheres coherently coupled to a cavity mode, in which the CPA EP3 is realized by engineering the three-mode loss to form a pseudo-Hermitian absorption Hamiltonian. By independently tailoring the absorption EP apart from the resonance EP, the system circumvents the noise divergence caused by eigenbasis collapse. Notably, we harness the sensitivity of the minimum output intensity near CPA to perturbations, yielding a seventyfold SNR improvement and a 400-fold increase in responsivity compared with non-CPA system. A comprehensive noise analysis over one hundred repeated measurements confirms the suppression of frequency noise near the CPA EP3. This demonstrates that our scheme not only avoids the noise divergence plaguing conventional higher-order EP sensors but also provides a general strategy to exploit both CPA and EP for SNR enhancement in passive non-Hermitian systems.