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Exceptional points (EPs), singularities of non-Hermitian physics where complex spectral resonances degenerate, are one of the most exotic features of nonequilibrium open systems with unique properties. For instance, the emission rate of…

We review some recent work on the occurrence of coalescing eigenstates at exceptional points in non-Hermitian systems and their influence on physical quantities. We particularly focus on quantum dynamics near exceptional points in open…

Quantum Physics · Physics 2021-10-27 Savannah Garmon , Takafumi Sawada , Kenichi Noba , Gonzalo Ordonez

Exceptional points (EPs) are degeneracy of non-Hermitian Hamiltonians, at which the eigenvalues, along with their eigenvectors, coalesce. Their orders are given by the Jordan decomposition. Here, we focus on higher-order EPs arising in…

Quantum Physics · Physics 2023-04-18 Kang Yang , Ipsita Mandal

Exceptional points play a pivotal role in the topology of non-Hermitian systems, and significant advances have been made in classifying exceptional points and exploring the associated phenomena. Exceptional surfaces, which are hypersurfaces…

Materials Science · Physics 2022-09-08 Hongwei Jia , Ruo-Yang Zhang , Jing Hu , Yixin Xiao , Yifei Zhu , C. T. Chan

At thermal equilibrium, we find that generalized susceptibilities encoding the static physical response properties of Hermitian many-electron systems possess inherent non-Hermitian (NH) matrix symmetries. This leads to the generic…

Strongly Correlated Electrons · Physics 2024-05-08 Matthias Reitner , Lorenzo Crippa , Dominik Robert Fus , Jan Carl Budich , Alessandro Toschi , Giorgio Sangiovanni

Exceptional points (EPs) are spectral degeneracies unique to non-Hermitian systems which underpin phenomena from enhanced sensing to unconventional topology. While disorder is usually viewed as detrimental, it can also drive topological…

Disordered Systems and Neural Networks · Physics 2026-01-28 Xiaoyu Cheng , Tiantao Qu , Yaqing Yang , Jun Chen , Lei Zhang

We study the interplay of two distinct non-Hermitian parameters: directional coupling and onsite gain-loss, together with topology, in coupled one-dimensional (1D) non-Hermitian Su-Schrieffer-Heeger (SSH) chains. The SSH model represents…

Mesoscale and Nanoscale Physics · Physics 2023-08-14 Sayan Jana , Lea Sirota

Non-Hermitian systems can produce branch singularities known as exceptional points (EPs). Different from singularities in Hermitian systems, the topological properties of an EP can involve either the winding of eigenvalues that produces a…

Quantum Physics · Physics 2021-07-21 Weiyuan Tang , Kun Ding , Guancong Ma

A pair of anisotropic exceptional points (EPs) of arbitrary order are found in a class of non-Hermitian random systems with asymmetric hoppings. Both eigenvalues and eigenvectors exhibit distinct behaviors when these anisotropic EPs are…

Mesoscale and Nanoscale Physics · Physics 2019-06-12 Yi-Xin Xiao , Zhao-Qing Zhang , Zhi Hong Hang , C. T. Chan

Exceptional points~(EPs) appear as degeneracies in the spectrum of non-Hermitian matrices at which the eigenvectors coalesce. In general, an EP of order $n$ may find room to emerge if $2(n-1)$ real constraints are imposed. Our results show…

Quantum Physics · Physics 2022-07-29 Sharareh Sayyad , Flore K. Kunst

Exceptional points are universal level degeneracies induced by non-Hermiticity. Whereas past decades witnessed their new physics, the unified understanding has yet to be obtained. Here we present the complete classification of generic…

Mesoscale and Nanoscale Physics · Physics 2019-08-13 Kohei Kawabata , Takumi Bessho , Masatoshi Sato

We consider different properties of small open quantum systems coupled to an environment and described by a non-Hermitian Hamilton operator. Of special interest is the non-analytical behavior of the eigenvalues in the vicinity of singular…

Quantum Physics · Physics 2015-04-15 Hichem Eleuch , Ingrid Rotter

Non-Hermitian systems can manifest rich static and dynamical properties at their exceptional points (EPs). Here, we identify yet another class of distinct phenomena that is hinged on EPs, namely, the emergence of a series of non-Hermitian…

Quantum Physics · Physics 2025-04-03 Zuo Wang , Liang He

As an exclusive feature of a non-Hermitian system, the existence of exceptional points (EPs) depends not only on the details of the Hamiltonian but also on the particle-number filling and the particle statistics. In this paper, we study…

Strongly Correlated Electrons · Physics 2025-09-24 J. Y. Liu-Sun , Z. Song

Exceptional points (EPs) are remarkable spectral degeneracies in a non-Hermitian system's parameter space, where both eigenvalues and eigenstates coalesce. Here, we show that in non-Hermitian molecular chiral systems the position of EPs in…

Quantum Physics · Physics 2025-12-02 Nicola Mayer , Alexander Löhr , Nimrod Moiseyev , Misha Ivanov , Olga Smirnova

Exceptional points (EPs), arising in non-Hermitian systems, have garnered significant attention in recent years, enabling advancements in sensing, wave manipulation, and mode selectivity. However, their role in quantum systems, particularly…

Quantum Physics · Physics 2026-01-21 Chenghe Yu , Mingsheng Tian , Ningxin Kong , Matteo Fadel , Xinyao Huang , Qiongyi He

Non-Hermitian systems hosting exceptional points (EPs) exhibit signal enhancement and unconventional mode dynamics. Going beyond isolated EPs, here we report on the existence of exceptional rings (ERs) in planar optical resonators with…

Exceptional point (EP) associated with eigenstates coalescence in non-Hermitian systems has many exotic features. The EPs are generally sensitive to system parameters, here we report symmetry protected isolated EPs in the Brillouin zone…

Quantum Physics · Physics 2019-05-07 S. Lin , L. Jin , Z. Song

Exceptional points (EPs), ubiquitous non-Hermitian degeneracies, are central features in band structures where non-Hermitian Fermi arcs connect EPs and eigenvalue knots encircle them. Under open boundary conditions (OBCs), non-Hermitian…

Other Condensed Matter · Physics 2026-01-06 Yuancheng Zhao , Jia-Xin Zhong , Jing Lin , Yun Jing , Kun Ding

The classification of point gap topology in all local non-Hermitian symmetry classes has been recently established. However, many entries in the resulting periodic table have only been discussed in a formal setting and still lack a physical…

Mesoscale and Nanoscale Physics · Physics 2023-09-04 M. Michael Denner , Titus Neupert , Frank Schindler