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Exceptional points (EPs) are special spectral degeneracies of non-Hermitian operators: at the EP, the complex eigenvalues coalesce, i.e., they become degenerate in both their real and imaginary parts. In two-dimensional (2D) photonic…

Optics · Physics 2025-06-17 Luigi Frau , Simone Zanotti , Lydie Ferrier , Dario Gerace , Hai Son Nguyen

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

Non-Hermitian systems with anti-parity-time ($\mathcal{APT}$) symmetry have revealed rich physics beyond conventional systems. Here, we study optomechanics in an $\mathcal{APT}$-symmetric spinning resonator and show that, by tuning the…

Quantum Physics · Physics 2023-03-29 Meiyu Peng , Huilai Zhang , Qian Zhang , Tian-Xiang Lu , Imran M. Mirza , Hui Jing

The frozen mode regime is a unique slow-light scenario in periodic structures, where the flat-bands (zero group velocity) are associated with the formation of high-order stationary points (aka exceptional points). The formation of…

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

Exceptional points (EPs) are spectral defects displayed by non-Hermitian systems in which multiple degenerate eigenvalues share a single eigenvector. This distinctive feature makes systems exhibiting EPs more sensitive to external…

Quantum Physics · Physics 2025-12-11 Subhajyoti Bid , Henning Schomerus

In a non-Hermitian optical system with loss and gain, an exceptional point (EP) will arise under specific parameters where the eigenvalues and eigenstates exhibit simultaneous coalescence. Here we report a dynamical switching of lasing…

Optics · Physics 2019-12-30 Yicong Zhang , Weiwei Liu , Qingjie Liu , Bing Wang , Peixiang Lu

Exceptional points, with simultaneous coalescence of eigen-values and eigen-vectors, can be realized with non-Hermitian photonic systems. With the enhanced response, exceptional points have been proposed to improve the performance of…

Optics · Physics 2022-07-22 Dalton Anderson , Manav Shah , Linran Fan

The simultaneous existence of coherent perfect absorption (CPA) and lasing is one of the most intriguing features of non-Hermitian photonics. However, the link between CPA lasing and PT symmetry breaking at the exceptional point (EP) needs…

Optics · Physics 2019-08-14 Denis Novitsky

Exceptional points(EPs), branch points of complex energy surfaces at which eigenvalues and eigenvectors coalesce, are ubiquitous in non-Hermitian systems. Many novel properties and applications have been proposed around the EPs. One of the…

Higher-order exceptional points (EPs), resulting from non-Hermitian degeneracies, have shown greater advantages in sensitive enhancement than second-order EPs (EP2s). Therefore, seeking higher-order EPs in various quantum systems is…

Quantum Physics · Physics 2021-12-15 Wei Xiong , Zhuanxia Li , Yiling Song , Jiaojiao Chen , Guoqiang Zhang , Mingfeng Wang

Exceptional points (EPs) -- singularities in the parameter space of non-Hermitian systems where two nearby eigenmodes coalesce -- feature unique properties with applications such as sensitivity enhancement and chiral emission. Existing…

Optics · Physics 2024-10-08 Xingwei Gao , Hao He , Scott Sobolewski , Alexander Cerjan , Chia Wei Hsu

We demonstrate the existence of exceptional points of degeneracy (EPD) of periodic eigenstates in non-Hermitian coupled chains of dipolar scatterers. Guided modes supported by these structures can exhibit an EPD in their dispersion diagram…

Optics · Physics 2017-03-22 Mohamed A. K. Othman , Vincenzo Galdi , Filippo Capolino

Quantum sensing near exceptional points (EPs) in non-Hermitian systems has shown promising sensitivity enhancements. However, practical applications are often hindered by structural complexity and strict parameter constraints. In this work,…

Quantum Physics · Physics 2026-02-27 Hao-Wen Zhang , Dong-Yang Wang , Cheng-Hua Bai , Tian-Xiang Lu , Shi-Lei Su

We observe natural exceptional points in the excitation spectrum of an exciton-polariton system by optically tuning the light-matter interactions. The observed exceptional points do not require any spatial or polarization degrees of freedom…

Numerical simulations based on the quantum Langevin equations have been performed for a large number of two-level atoms in a beam interacting with a low-Q cavity with the atomic initial superposition states close to the north pole of the…

Quantum Physics · Physics 2024-08-20 Mingyu Jeon , Jinuk Kim , Kyungwon An

We show that the timed Dicke states of a collection of three-level atoms can form a tight-binding lattice in momentum space. This lattice, coined the superradiance lattice (SL), can be constructed based on electromagnetically induced…

Atomic Physics · Physics 2015-01-29 Da-Wei Wang , Ren-Bao Liu , Shi-Yao Zhu , Marlan O. Scully

We demonstrate how to realize an optical clock with neutral atoms that is competitive to the currently best single ion optical clocks in accuracy and superior in stability. Using ultracold atoms in a Ca optical frequency standard we show…

Atomic Physics · Physics 2009-11-07 G. Wilpers , T. Binnewies , C. Degenhardt , U. Sterr , J. Helmcke , F. Riehle

An oscillator array prefers to operate at an exceptional point of degeneracy (EPD) occurring in a waveguide periodically loaded with discrete nonlinear gain and radiating elements. The system maintains a steady-state degenerate mode of…

Optics · Physics 2023-08-10 Alireza Nikzamir , Filippo Capolino

Steady-state superradiance and superradiant lasing attract significant attentions in the field of optical lattice clocks, but have not been achieved so far due to the technical challenges and atom loss problem. In this article, we propose…

Quantum Physics · Physics 2022-12-06 Qilong Wu , Yuan Zhang , Hao Wu , Shi-Lei Su , Kai-Kai Liu , Mark Oxborrow , Chongxin Shan , Klaus Mølmer