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arXiv · 2601.17266

Exceptional-point-like Sensing near Hermitian Critical Points

Jiang-Shan Tang·Long-Qi Xiao·Hao-Dong Wu·Yuwei Jing·Han Zhang·Ya-Ping Ruan·Wuming Liu·Yan-Qing Lu·Keyu Xia
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Abstract

A non-Hermitian system at an exceptional point (EP), a specific critical point (CP) associated with the parity-time symmetric phase transition, exhibits a sublinear response to perturbation and promise unprecedented sensitivity beyond the linear-response Hermitian sensors, so far operating at the diabolic points (DP). Despite great advancements, its sensitivity enhancement is fundamentally limited by the divergent Petermann factor, intrinsically rooted in the non-Hermitian eigenvector degeneracy, and practically by the system complexity. Here, we report the CP-resulting square-root response to the refractive index change and enhanced sensitivity in a simple chiral Hermitian cavity without phase transitions. Because of the inherent eigenvector orthogonality, this CP-based Hermitian sensor exhibits an EP-like response and enhanced sensitivity, breaking the Petermann-factor limit of sensitivity in non-Hermitian counterparts. This work paves the way towards exploring the Hermitian CPs for ultrasensitive sensing outperforming both the EP- and DP-based sensors.

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Jiang-Shan Tang, Long-Qi Xiao, Hao-Dong Wu, Yuwei Jing, Han Zhang, Ya-Ping Ruan, Wuming Liu, Yan-Qing Lu, Keyu Xia. 2026-01-24. Exceptional-point-like Sensing near Hermitian Critical Points. https://arxiv.org/abs/2601.17266

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