近日，南京大学范克彬团队研究了从连续统中的束缚态导出的光开关异常点。2025年10月28日出版的《光：科学与应用》杂志发表了这项成果。

连续统中的束缚态（BICs）和异常点（EPs）作为非厄米系统中由复频率表示的两种不同的物理奇点，近年来在各自的领域得到了极大的关注和明确的定义。它们在高灵敏度传感和激光发射等领域有重叠的应用。然而，两者之间的过渡，受到这些交集的启发，在很大程度上仍未被探索。

在这项工作中，研究组揭示了非厄米双模系统从单界奇点到二维异常环的转变过程，其中EP是准Friedrich Wintgen（FW）-BIC的合并态。这种现象在太赫兹波段的多孔介质超表面上得到了实验验证。此外，外部泵浦诱导光载流子作为耗散扰动，有助于打破复特征频率的简并并实现动态EP切换。最后，研究组通过实验证明了一种可切换的太赫兹波束偏转是由极电磁波的相位奇点驱动的。这些发现有助于推进非厄米系统中用于传感和波前控制的紧凑型设备的发展。

附：英文原文

Title: Photoswitchable exceptional points derived from bound states in the continuum

Author: Wang, Lei, Liu, Hang, Liu, Junwei, Liu, Aoxuan, Huang, Jialiang, Li, Qiannan, Dai, Hui, Zhang, Caihong, Wu, Jingbo, Fan, Kebin, Wang, Huabing, Jin, Biaobing, Chen, Jian, Wu, Peiheng

Issue&Volume: 2025-10-28

Abstract: Bound states in the continuum (BICs) and exceptional points (EPs), as two distinct physical singularities represented by complex frequencies in non-Hermitian systems, have garnered significant attention and clear definitions in their respective fields in recent years. They share overlapping applications in areas such as high-sensitivity sensing and laser emission. However, the transition between the two, inspired by these intersections, remains largely unexplored. In this work, we reveal the transition process in a non-Hermitian two-mode system, evolving from one bound singularity to a two-dimensional exceptional ring, where the EP is the coalescent state of the quasi-Friedrich-Wintgen (FW)-BIC. This phenomenon is experimentally validated through pored dielectric metasurfaces in terahertz band. Furthermore, external pumping induced photocarriers as the dissipative perturbation, facilitates the breaking of degeneracy in the complex eigenfrequency and enables dynamic EP switching. Finally, we experimentally demonstrate a switchable terahertz beam deflection driven by the phase singularities of the EP. These findings are instrumental in advancing the development of compact devices for sensing and wavefront control within non-Hermitian systems.

DOI: 10.1038/s41377-025-02036-0

Source: https://www.nature.com/articles/s41377-025-02036-0