Abstract:

Defective spectral degeneracy, known as exceptional point (EP), lies at the heart of a variety of intriguing phenomena in optics, acoustics, cold atoms, and other non-conservative systems. Despite extensive studies in the past two decades, a holistic framework accounting for the collective behaviors (e.g., annihilation, coalescence, braiding, etc.) involving multiple exceptional points or lines and their interplay is still lacking. Here we formulate an exceptional band theory by exploiting based homotopy groups and put forward a universal non-Abelian conservation rule governing these collective phenomena in generic multiband non-Hermitian systems. Starting from this framework, we uncover several counter-intuitive 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 non-Abelian conservation rule imposes strict constraints on the permissible exceptional-line configurations. It excludes structures like Hopf link yet permits novel staggered rings composed of non-commutative exceptional lines. These intriguing phenomena are illustrated by concrete models and could be readily implemented in platforms like coupled acoustic cavities. 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 non-conservative systems.

Bio:

中國(guó)科學(xué)院物理研究所“百人特聘研究員”，博士生導(dǎo)師。2011年9月畢業(yè)于中國(guó)科學(xué)技術(shù)大學(xué)零零班。2016年7月在中國(guó)科學(xué)院物理研究所獲得物理博士學(xué)位。2016年9月-2021年9月分別在德州大學(xué)達(dá)拉斯分校，匹茲堡大學(xué)和喬治梅森大學(xué)從事博士后研究。2021年9月加入中國(guó)科學(xué)院物理研究所。主要研究方向?yàn)橥負(fù)淠蹜B(tài)理論，量子動(dòng)力學(xué)，原子分子與光物理和量子模擬理論。