报告题目：Non-Abelian aspects of non-Hermitian bands and exceptional degeneracies

报告人：胡海平研究员    中国科学院物理研究所

报告时间：2023年10月26日（周四）15:00

报告地点：理六栋302        邀请人：朱诗亮

报告内容：

Defective spectral degeneracy, known as exceptional point (EP), lies at the heart of various intriguingphenomena in optics, acoustics, and other nonconservative systems. In this presentation, we provide a topological classification of isolated exceptional degeneracies based on homotopy theory. We then put forward a universal non-Abelian conservation rule governing the collective behaviors (e.g.,annihilation, coalescence, braiding, etc.) in generic non-Hermitian systems and uncover several counterintuitive phenomena. We demonstrate that two EPs with opposite charges (even the pairwise created) do not necessarily annihilate, depending on how they approach each other. Furthermore, we unveil that the conservation rule imposes strict constraints on the permissible exceptional-line configurations. It excludes structures like Hopf link yet permits novel staggered rings composed of noncommutative exceptional lines. These intriguing phenomena are illustrated by concrete models which could bereadily implemented in platforms like coupled acoustic cavities, optical waveguides, and ring resonators. Our findings lay the cornerstone for a comprehensive understanding of the exceptional non-Abelian topology and shed light on the versatile manipulations and applications based on exceptional degeneracies in nonconservative systems.

专家简介：

胡海平，中国科学院物理研究所“百人特聘研究员”，博导。2007年8月-2011年9月进入中国科学技术大学零零班学习。2016年7月在中国科学院物理研究所获得物理博士学位。2016年9月赴德州大学达拉斯分校从事博士后研究，2018年9月-2021年8月年于匹兹堡大学和乔治梅森大学从事博士后研究。2021年9月加入中国科学院物理研究所。主要研究方向为拓扑凝聚态物理及量子模拟，非平衡量子动力学，自旋轨道耦合超冷原子系统及非厄米物理理论。