实验观测非厄米系统奇异点的手性翻转现象  

Experimental observation of chiral inversion at exceptional points of non-Hermitian systems

作　　者：祝可嘉 郭志伟[2] 陈鸿[2] Zhu Ke-Jia;Guo Zhi-Wei;Chen Hong(Department of Electrical Engineering,Tongji University,Shanghai 200092,China;Key Laboratory of Advanced Micro-structured Materials,Ministry of Education,School of Physics Sciences and Engineering,Tongji University,Shanghai 200092,China)

机构地区：[1]同济大学电子与信息工程学院,上海200092 [2]同济大学物理科学与工程学院,教育部先进微结构材料重点实验室,上海200092

出　　处：《物理学报》2022年第13期89-96,共8页Acta Physica Sinica

基　　金：国家重点研发计划(批准号:2021YFA1400602);国家自然科学基金(批准号:12004284,61621001);中央高校基本科研业务费(批准号:22120210579);上海市晨光计划(批准号:21CGA22)资助的课题。

摘　　要：在非厄米系统参数空间的黎曼曲面上存在简并点,此时本征值和相应的本征矢量同时合并,这些非厄米简并点也被称为奇异点.作为非厄米物理系统的相变临界态,奇异点会引起诸多违反直觉的现象,如损耗诱导透明、单向隐身以及非对称的模式转换.特别有趣的是,奇异点的本征矢量是自正交的,并且由于维度的缺失,特定非厄米系统的奇异点具有固有的手性.本文基于开口谐振环这种特殊的超构材料谐振子构造了耦合系数符号可以灵活调控的非厄米系统,并在实验上观测了非厄米系统奇异点的手性翻转现象.利用耦合系数符号的改变来实现非厄米系统奇异点的手性态调控,不仅为研究开放系统中的基本非厄米物理开辟了一条新的途径,而且在设计高效手性模式转换以及手性天线等光子器件方面具有一定的应用价值.Based on the quantum mechanics,the physical observables are represented by Hermitian linear operators.Derived from the conservation of energy,these Hermitian operators exhibit real eigenvalues.However,when a closed system described by an effective Hamiltonian is coupled with the surrounding environment,the dynamics of the system itself becomes non-Hermitian dynamic.In general,the eigenvalues of an open optical non-Hermitian system are complex.Parity-time symmetric structure is the system composed of complex potentials,which is neither parity symmetric nor time reversal symmetric alone but is symmetric after operations of parity inversion and time reversal have been combined.The eigenvalue of the parity-time symmetric Hamiltonian can be found to be real,despite the non-Hermitian nature of the system.One of the most attractive properties of non-Hermitian system is the exceptional point,which is degenerate at which two or more eigenvalues and eigenstates of a non-Hermitian physical system coalesce.The unique topological features of EPs,forming a self-intersecting Riemann surface,have given rise to several exotic physical properties.As a kind of phase singularity in a physical system,exceptional point of non-Hermitian system gives rise to a plethora of counterintuitive phenomenon,such as the loss-induced transmission enhancement,unidirectional reflection and asymmetric state transfer.Especially,the eigenvectors of exceptional point are self-orthogonal and an inherent chirality can be determined because of the missing dimension.Chirality lies at the heart of the most fascinating and fundamental phenomena in modern physics,and how to impose a strong chirality and a switchable direction of light propagation in an optical system by steering it to an exceptional point is an interesting research topic.In this work,a non-Hermitian system is constructed based on the special metamaterial resonator of split-ring resonator,in which the sign of coupling coefficient can be flexibly controlled.Especially,the chiral inversion at an

关 键 词：非厄米系统 超构材料谐振子 奇异点 手性态 

分 类 号：O413.1[理学—理论物理]