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Exceptional points (EPs), at which both eigenvalues and eigenvectors coalesce, are ubiquitous and unique features of non-Hermitian systems. Second-order EPs are by far the most studied due to their abundance, requiring only the tuning of…

Optics · Physics 2023-01-02 Ipsita Mandal , Emil J. Bergholtz

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

We investigate the existence of higher order exceptional points (EPs) in non-Hermitian systems, and show that $\mu$-fold EPs are stable in $\mu-1$ dimensions in the presence of anti-unitary symmetries that are local in parameter space, such…

Mesoscale and Nanoscale Physics · Physics 2021-10-27 Pierre Delplace , Tsuneya Yoshida , Yasuhiro Hatsugai

Exceptional points (EPs) of non-Hermitian (NH) systems have recently attracted increasing attention due to their rich phenomenology and intriguing applications. Compared to the predominantly studied second-order EPs, higher-order EPs have…

Mesoscale and Nanoscale Physics · Physics 2023-09-07 Kunkun Wang , Lei Xiao , Haiqing Lin , Wei Yi , Emil J. Bergholtz , Peng Xue

Exceptional points (EPs) are degeneracies in open wave systems with coalescence of at least two energy levels and their corresponding eigenstates. In higher dimensions, more complex EP physics not found in two-state systems is observed. We…

Exceptional points (EPs) are non-Hermitian spectral degeneracies marking a simultaneous coalescence of eigenvalues and eigenvectors. Despite the fact that multiband $n$-fold EPs (EP$n$s) generically emerge as special points on manifolds of…

Optics · Physics 2026-03-16 Anton Montag , Jordan Isaacs , Marcus Stålhammar , Flore K. Kunst

Exceptional points (EPs) are central to non-Hermitian physics because of their unique properties and broad application prospects. While extensively studied in parity-time ($\mathcal{P}\mathcal{T}$)-symmetric systems and under Markovian…

Optics · Physics 2026-01-15 H. Z. Shen , X. C. Zhang , L. Y. Ning , Zhi-Guang Lu , Yan-Hui Zhou , Cheng Shang

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

Non-Hermitian (NH) Hamiltonians have become an important asset for the effective description of various physical systems that are subject to dissipation. Motivated by recent experimental progress on realizing the NH counterparts of gapless…

Mesoscale and Nanoscale Physics · Physics 2019-01-30 Jan Carl Budich , Johan Carlström , Flore K. Kunst , Emil J. Bergholtz

One of the unique features of non-Hermitian~(NH) systems is the appearance of non-Hermitian degeneracies known as exceptional points~(EPs). The extensively studied defective EPs occur when the Hamiltonian becomes non-diagonalizable. Aside…

Quantum Physics · Physics 2023-12-11 Sharareh Sayyad , Marcus Stalhammar , Lukas Rodland , Flore K. Kunst

In non-Hermitian systems, the defective band degeneracies, so-called exceptional points (EPs), can form robust exceptional lines (ELs) in 3D momentum space in the absence of any symmetries. Here, we show that a natural orientation can be…

Optics · Physics 2022-12-13 Ruo-Yang Zhang , Xiaohan Cui , Wen-Jie Chen , Zhao-Qing Zhang , C. T. Chan

Exceptional points (EPs), at which more than one eigenvalue and eigenvector coalesce, are unique spectral features of Non-Hermiticity (NH) systems. They exist widely in open systems with complex energy spectra. We experimentally demonstrate…

Exceptional points (EPs) has seen substantial advances in both experiment and theory. However, in quantum systems, higher-order exceptional points remain of great interest and possess numerous intriguing properties yet to be fully explored.…

Quantum Gases · Physics 2025-01-22 Yu-Jun Liu , Ka Kwan Pak , Peng Ren , Mengbo Guo , Entong Zhao , Chengdong He , Gyu-Boong Jo

Higher-order exceptional points (EPs), which appear as multifold degeneracies in the spectra of non-Hermitian systems, are garnering extensive attention in various multidisciplinary fields. However, constructing higher-order EPs still…

Higher-order exceptional points (EPs) in non-Hermitian systems showcase diverse physical phenomena but require more parameter space freedom or symmetries. It leads to a challenge for the exploration of high-order EP geometries in…

Quantum Physics · Physics 2025-10-22 Hao Chen , Xiao Qin , Jian-Jun Dong , Yu-Yu Zhang , Zi-Xiang Hu

Exceptional points (EPs), i.e., non-Hermitian degeneracies at which eigenvalues and eigenvectors coalesce, can be realized by tuning the gain/loss contrast of different modes in non-Hermitian systems or by engineering the asymmetric…

Exceptional points (EPs) determine the dynamics of open quantum systems and cause also PT symmetry breaking in PT symmetric systems. From a mathematical point of view, this is caused by the fact that the phases of the wavefunctions…

Dynamical Systems · Mathematics 2014-04-30 Hichem Eleuch , Ingrid Rotter

The exceptional points (EPs) aroused from the non-Hermiticity bring rich phenomena, such as exceptional nodal topologies, unidirectional invisibility, single-mode lasing, sensitivity enhancement and energy harvesting. Isolated high-order…

Quantum Physics · Physics 2024-01-19 Yang Wu , Yunhan Wang , Xiangyu Ye , Wenquan Liu , Zhibo Niu , Chang-Kui Duan , Ya Wang , Xing Rong , Jiangfeng Du

Exceptional points (EPs) are non-Hermitian degeneracies where eigenvalues and eigenvectors coalesce, giving rise to unusual physical effects across scientific disciplines. The concept of EPs has recently been extended to nonlinear physical…

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
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