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Non-hermitian skin effect and delocalized edge states in photonic crystals with anomalous parity-time symmetry

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arXiv 2021年

作者： Yan, Qinghui Chen, Hongsheng Yang, Yihao Interdisciplinary Center for Quantum Information State Key Laboratory of Modern Optical Instrumentation ZJU-Hangzhou Global Scientific and Technological Innovation Center Zhejiang University Hangzhou310027 China International Joint Innovation Center Key Lab. of Advanced Micro/Nano Electronic Devices & Smart Systems of Zhejiang Electromagnetics Academy at Zhejiang University Zhejiang University Haining314400 China

Non-Hermitian skin effect denotes the exponential localization of a large number of eigen-states in a non-Hermitian lattice under open boundary conditions. Such a non-Hermiticity-induced skin effect can offset the penetration depth of in-gap edge states, leading to counterintuitive delocalized edge modes, which have not been studied in a realistic photonic system such as photonic crystals. Here, we analytically reveal the non-Hermitian skin effect and the delocalized edge states in Maxwell’s equations for non-Hermitian chiral photonic crystals with anomalous parity-time symmetry. Remarkably, we rigorously prove that the penetration depth of the edge states is inversely proportional to the frequency and the real part of the chirality. Our findings pave a way towards exploring novel non-Hermitian phenomena and applications in continuous Maxwell’s equations. © 2021, CC0.

关键词： Crystal symmetry

Topological chiral edge states in deep-subwavelength valley photonic metamaterials

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arXiv 2021年

作者： Xi, Rui Chen, Qiaolu Yan, Qinghui Zhang, Li Chen, Fujia Li, Ying Chen, Hongsheng Yang, Yihao Interdisciplinary Center for Quantum Information State Key Laboratory of Modern Optical Instrumentation ZJU-Hangzhou Global Scientific and Technological Innovation Center Zhejiang University Hangzhou310027 China International Joint Innovation Center Key Lab. of Advanced Micro/Nano Electronic Devices and Smart Systems of Zhejiang The Electromagnetics Academy at Zhejiang University Zhejiang University Haining314400 China

Topological valley photonics has emerged as a new frontier in photonics with many promising applications. Previous valley boundary transport relies on kink states at internal boundaries between two topologically distinct domains. However, recent studies have revealed a novel class of topological chiral edge states (CESs) at external boundaries of valley materials, which have remained elusive in photonics. Here, we propose and experimentally demonstrate the topological CESs in valley photonic metamaterials (VPMMs) by accurately tuning on-site edge potentials. Moreover, the VPMMs work at deep-subwavelength scales. Thus, the supported CESs are highly confined and self-guiding without relying on a cladding layer to prevent leakage radiation. Via direct near-field measurements, we observe the bulk bandgap, the edge dispersions, and the robust edge transport passing through sharp corners, which are hallmarks of the CESs. Our work paves a way to explore novel topological edge states in valley photonics and sheds light on robust and miniaturized photonic devices. © 2021, CC BY.

关键词： Landforms

Non-Hermitian Dirac cones with valley-dependent lifetimes

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arXiv 2024年

作者： Xie, Xinrong Ma, Fei Rui, W.B. Dong, Zhaozhen Du, Yulin Xie, Wentao Zhao, Y.X. Chen, Hongsheng Gao, Fei Xue, Haoran State Key Laboratory of Extreme Photonics and Instrumentation International Joint Innovation Center The Electromagnetics Academy Zhejiang University Zhejiang University Haining314400 China ZJU-Hangzhou Global Scientific and Technological Innovation Center Zhejiang University Hangzhou310027 China Key Lab. of Advanced Micro/Nano Electronic Devices & Smart Systems of Zhejiang Jinhua Institute of Zhejiang University Zhejiang University Jinhua321099 China Shaoxing Institute of Zhejiang University Zhejiang University Shaoxing312000 China Department of Physics HKU-UCAS Joint Institute for Theoretical and Computational Physics at Hong Kong The University of Hong Kong Pokfulam Road Hong Kong HK Institute of Quantum Science & Technology The University of Hong Kong Pokfulam Road Hong Kong Department of Physics The Chinese University of Hong Kong Shatin Hong Kong

Relativistic quasiparticles emerging from band degeneracies in crystals play crucial roles in the transport and topological properties of materials and metamaterials. Quasiparticles are commonly described by Hermitian Hamiltonians, with non-Hermiticity usually considered detrimental. In this work, we show that such an assumption of Hermiticity can be lifted to bring quasiparticles into non-Hermitian regime. We propose a concrete lattice model containing two Dirac cones with valley-dependent lifetimes. The lifetime contrast enables an ultra-strong valley selection rule: only one valley can survive in the long-time limit regardless of the excitation, lattice shape and other details. This property leads to an effective parity anomaly with a single Dirac cone and offers a simple way to generate vortex states. Additionally, extending non-Hermitian features to boundaries generates valley kink states with valley-locked lifetimes, making them effectively unidirectional and more resistant against inter-valley scattering. All these phenomena are experimentally demonstrated in a non-Hermitian electric circuit lattice. Copyright © 2024, The Authors. All rights reserved.

关键词： Topology

A brief review of topological photonics in one, two, and three dimensions

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arXiv 2022年

作者： Lan, Zhihao Chen, Menglin L.N. Gao, Fei Zhang, Shuang Sha, Wei E.I. Department of Electronic and Electrical Engineering University College London Torrington Place LondonWC1E 7JE United Kingdom Department of Physics The University of Hong Kong Hong Kong Interdisciplinary Center for Quantum Information State Key Laboratory of Modern Optical Instrumentation ZJU-Hangzhou Global Science and Technology Innovation Center College of Information Science and Electronic Engineering Zhejiang University Hangzhou China Department of Electrical and Electronic Engineering The University of Hong Kong Hong Kong Key Laboratory of Micro-Nano Electronic Devices and Smart Systems of Zhejiang Province College of Information Science and Electronic Engineering Zhejiang University Hangzhou310027 China

Topological photonics has attracted increasing attention in recent years due to the unique opportunities it provides to manipulate light in a robust way immune to disorder and defects. Up to now, diverse photonic platforms, rich physical mechanisms and fruitful device applications have been proposed for topological photonics, including one-way waveguide, topological lasing, topological nanocavity, Dirac and Weyl points, Fermi arcs, nodal lines, etc. In this review, we provide an introduction to the field of topological photonics through the lens of topological invariants and bulk-boundary correspondence in one, two, and three dimensions, which may not only offer a unified understanding about the underlying robustness of diverse and distinct topological phenomena of light, but could also inspire further developments by introducing new topological invariants and unconventional bulk-boundary correspondence to the research of topological photonics. Copyright © 2022, The Authors. All rights reserved.

关键词： Photonics

Stochastic Exceptional Points for Noise-Assisted Sensing

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Physical Review Letters 2023年第22期130卷 227201-227201页

作者： Zhipeng Li Chenhui Li Ze Xiong Guoqiang Xu Yongtai Raymond Wang Xi Tian Xin Yang Zhu Liu Qihang Zeng Rongzhou Lin Ying Li Jason Kai Wei Lee John S. Ho Cheng-Wei Qiu Department of Electrical and Computer Engineering National University of Singapore Singapore 117583 Singapore Wireless and Smart Bioelectronics Lab School of Biomedical Engineering ShanghaiTech University Shanghai 201210 China Department of Physiology Yong Loo Lin School of Medicine National University of Singapore Singapore 117593 Singapore School of Physics and Electronics Hunan Normal University Changsha Hunan 410081 China Interdisciplinary Center for Quantum Information State Key Laboratory of Modern Optical Instrumentation ZJU-Hangzhou Global Scientific and Technological Innovation Center Zhejiang University Hangzhou 310027 China International Joint Innovation Center Key Lab of Advanced Micro/Nano Electronic Devices and Smart Systems of Zhejiang The Electromagnetics Academy of Zhejiang University Zhejiang University Haining 314400 China Heat Resilience and Performance Centre Yong Loo Lin School of Medicine National University of Singapore Singapore 119228 Singapore Human Potential Translational Research Programme Yong Loo Lin School of Medicine National University of Singapore Singapore 119228 Singapore

Noise is a fundamental challenge for sensors deployed in daily environments for ambient sensing, health monitoring, and wireless networking. Current strategies for noise mitigation rely primarily on reducing or removing noise. Here, we introduce stochastic exceptional points and show the utility to reverse the detrimental effect of noise. The stochastic process theory illustrates that the stochastic exceptional points manifest as fluctuating sensory thresholds that give rise to stochastic resonance, a counterintuitive phenomenon in which the added noise increases the system’s ability to detect weak signals. Demonstrations using a wearable wireless sensor show that the stochastic exceptional points lead to more accurate tracking of a person’s vital signs during exercise. Our results may lead to a distinct class of sensors that overcome and are enhanced by ambient noise for applications ranging from healthcare to the internet of things.

关键词： Noise Non-Hermitean systems PT-symmetry Noise measurements

A perspective on meta-boundaries

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arXiv 2022年

作者： Zhang, Xinyan Chen, Jialin Chen, Ruoxi Wang, Chan Cai, Tong Chen, Hongsheng Lin, Xiao Interdisciplinary Center for Quantum Information State Key Laboratory of Modern Optical Instrumentation ZJU-Hangzhou Global Scientific and Technological Innovation Center Zhejiang University Hangzhou310027 China International Joint Innovation Center Key Lab. of Advanced Micro/Nano Electronic Devices & Smart Systems of Zhejiang The Electromagnetics Academy Zhejiang University Zhejiang University Haining314400 China Department of Electrical and Computer Engineering Technion-Israel Institute of Technology Haifa32000 Israel Air and Missile Defense College Air Force Engineering University Xi’an710051 China

The judicious design of electromagnetic boundary provides a crucial route to control light-matter interactions, and it is thus fundamental to basic science and practical applications. General design approaches rely on the manipulation of bulk properties of superstrate or substrate and on the modification of boundary geometries. Due to the recent advent of metasurfaces and low-dimensional materials, the boundary can be flexibly featured with a surface conductivity, which can be rather complex but provide an extra degree of freedom to regulate the propagation of light. In this perspective, we denote the boundary with a non-zero surface conductivity as the meta-boundary. The meta-boundaries are categorized into four types, namely isotropic, anisotropic, biisotropic and bianisotropic meta-boundaries, according to the electromagnetic boundary conditions. Accordingly, the latest development for these four kinds of meta-boundaries are reviewed. Finally, an outlook on the research tendency of meta-boundaries is provided, particularly on the manipulation of light-matter interactions by simultaneously exploiting meta-boundaries and metamaterials. © 2022, CC BY.

关键词： Degrees of freedom (mechanics)

Spinful Topological Phases in Acoustic Crystals with Projective PT Symmetry

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Physical Review Letters 2023年第2期130卷 026101-026101页

作者： Yan Meng Shuxin Lin Bin-jie Shi Bin Wei Linyun Yang Bei Yan Zhenxiao Zhu Xiang Xi Yin Wang Yong Ge Shou-qi Yuan Jingming Chen Gui-Geng Liu Hong-xiang Sun Hongsheng Chen Yihao Yang Zhen Gao Department of Electrical and Electronic Engineering Southern University of Science and Technology Shenzhen 518055 China Research Center of Fluid Machinery Engineering and Technology School of Physics and Electronics Engineering Jiangsu University Zhenjiang 212013 China SKLSM Institute of Semiconductors Chinese Academy of Sciences Beijing 100083 China Center for Excellence in Topological Quantum Computation University of Chinese Academy of Sciences Beijing 100190 China Division of Physics and Applied Physics School of Physical and Mathematical Sciences Nanyang Technological University 21 Nanyang Link Singapore 637371 Singapore State Key Laboratory of Acoustics Institute of Acoustics Chinese Academy of Sciences Beijing 100190 China Interdisciplinary Center for Quantum Information State Key Laboratory of Extreme Photonics and Instrumentation ZJU-Hangzhou Global Scientific and Technological Innovation Center Zhejiang University Hangzhou 310027 China International Joint Innovation Center The Electromagnetics Academy at Zhejiang University Zhejiang University Haining 314400 China Key Lab. of Advanced Micro/Nano Electronic Devices & Smart Systems of Zhejiang Jinhua Institute of Zhejiang University Zhejiang University Jinhua 321099 China Shaoxing Institute of Zhejiang University Zhejiang University Shaoxing 312000 China

For the classification of topological phases of matter, an important consideration is whether a system is spinless or spinful, as these two classes have distinct symmetry algebra that gives rise to fundamentally different topological phases. However, only recently has it been realized theoretically that in the presence of gauge symmetry, the algebraic structure of symmetries can be projectively represented, which possibly enables the switch between spinless and spinful topological phases. Here, we report the experimental demonstration of this idea by realizing spinful topological phases in “spinless” acoustic crystals with projective space-time inversion symmetry. In particular, we realize a one-dimensional topologically gapped phase characterized by a 2Z winding number, which features double-degenerate bands in the entire Brillouin zone and two pairs of degenerate topological boundary modes. Our Letter thus overcomes a fundamental constraint on topological phases by spin classes.

关键词： Acoustics Edge states Topological insulators 1-dimensional systems Finite-element method Gauge symmetries Projective symmetries Tight-binding model

Metasurface tessellation for reconfigurable electromagnetic scattering

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arXiv 2020年

作者： Kong, Xiangdong Niu, Chuanning Zhao, Jia Wang, Zuojia School of Information Science and Engineering Shandong University Qingdao266237 China Key Laboratory of Advanced Micro/Nano Electronic Devices & Smart Systems of Zhejiang Electromagnetics Academy at Zhejiang University Zhejiang University Hangzhou310027 China

Metasurfaces have attracted significant research interest owing to their unprecedented control over the spatial distributions of electromagnetic fields. Herein we propose the concept of metasurface tessellation to achieve reconfigurable scattering functions. Square meta-tiles, composed of identical structures, are arranged to fill a surface. The electromagnetic scattering of the tiled surface is determined by the orientation distribution of the meta-tiles. We present three typical cases of meta-tiles consisting of binary elements to realize several distinct scattering patterns. This study provides an alternative method to build reconfigurable and multi-functional metasurface devices without external stimuli and complicated fabrication. Copyright © 2020, The Authors. All rights reserved.

关键词： Electromagnetic wave scattering

Diffusive nonreciprocity and thermal diode

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Physical Review B 2021年第1期103卷 014307-014307页

作者： Ying Li Jiaxin Li Minghong Qi Cheng-Wei Qiu Hongsheng Chen Interdisciplinary Center for Quantum Information State Key Laboratory of Modern Optical Instrumentation College of Information Science and Electronic Engineering Zhejiang University Hangzhou 310027 China ZJU-Hangzhou Global Science and Technology Innovation Center Key Lab. of Advanced Micro/Nano Electronic Devices & Smart Systems of Zhejiang Zhejiang University Hangzhou 310027 China International Joint Innovation Center ZJU-UIUC Institute The Electromagnetics Academy at Zhejiang University Zhejiang University Haining 314400 China Department of Electrical and Computer Engineering National University of Singapore Singapore 117583 Singapore State Key Laboratory of Robotics and System Harbin Institute of Technology Harbin 150001 China

Wave propagation and diffusion in linear materials preserve local reciprocity in terms of a symmetric Green's function. For wave propagations, the relation between the fields entering and leaving a system is more relevant than the detailed information about the fields inside it. In such cases, the global reciprocity of the scattering off a system through several ports is more important, which is defined as the symmetric transmission between the scattering channels. When a two-port system supports nonreciprocal (electromagnetic, acoustic) wave propagation, it is a (optical, phonon) diode directly following the definition. However, to date no concrete definition or discussion has been made on the global reciprocity of diffusive processes through a multiple-port system. It thus remains unclear what are the differences and relations between the three concepts, namely, local nonreciprocity, global nonreciprocity, and diode effect in diffusion. Here, we provide theoretical analysis on the frequency-domain Green's function and define the global reciprocity of heat diffusion through a two-port system, which has a different setup from that of a thermal diode. We further prove the equivalence between a heat transfer system with broken steady-state global reciprocity and a thermal diode, assuming no temperature-dependent heat generation. The validities of some typical mechanisms in breaking the diffusive reciprocity and making a thermal diode have been discussed. Our results set a general background for future studies on symmetric and asymmetric diffusive processes.

关键词： Diffusion Heat transfer Metamaterials Diodes Green's function methods