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Hou J, Zhu J, Ma R, Xue B, Zhu Y, Lin J, Jiang X, Zheng Y, Chen X, Cheng Y, Ge L, Wan W. Enhanced Frequency Conversion in Parity-Time Symmetry Line. PHYSICAL REVIEW LETTERS 2024; 132:256902. [PMID: 38996261 DOI: 10.1103/physrevlett.132.256902] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/07/2023] [Accepted: 05/09/2024] [Indexed: 07/14/2024]
Abstract
Non-Hermitian degeneracies reveal intriguing and nontrivial behaviors in open physical systems. Examples like parity-time (PT) symmetry breaking, topological encircling chirality, and enhanced sensing near an exceptional point (EP) are often associated with the abrupt nature of the phase transition around these degeneracies. Here we experimentally observe a cavity-enhanced second-harmonic frequency (SHG) conversion on a PT symmetry line, i.e., a set consisting of open-ended isofrequency or isoloss lines, both terminated at EPs on the Riemann surface in parameter space. The enhancement factor can reach as high as 300, depending on the crossing point whether in the symmetry or the broken phase of the PT line. Moreover, such enhancement of SHG enables sensitive distance sensing with a nanometer resolution. Our works may pave the way for practical applications in sensing, frequency conversion, and coherent wave control.
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Affiliation(s)
- Jiankun Hou
- State Key Laboratory of Advanced Optical Communication Systems and Networks, University of Michigan-Shanghai Jiao Tong University Joint Institute, Shanghai Jiao Tong University, Shanghai 200240, China
| | | | - Ruixin Ma
- State Key Laboratory of Advanced Optical Communication Systems and Networks, University of Michigan-Shanghai Jiao Tong University Joint Institute, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Boyi Xue
- State Key Laboratory of Advanced Optical Communication Systems and Networks, University of Michigan-Shanghai Jiao Tong University Joint Institute, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Yicheng Zhu
- State Key Laboratory of Advanced Optical Communication Systems and Networks, University of Michigan-Shanghai Jiao Tong University Joint Institute, Shanghai Jiao Tong University, Shanghai 200240, China
| | | | - Xiaoshun Jiang
- National Laboratory of Solid-State Microstructures, College of Engineering and Applied Science and School of Physics, Nanjing University, Nanjing 210093, China
| | | | | | - Ya Cheng
- National Laboratory of Solid-State Microstructures, College of Engineering and Applied Science and School of Physics, Nanjing University, Nanjing 210093, China
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Longhi S. Incoherent non-Hermitian skin effect in photonic quantum walks. LIGHT, SCIENCE & APPLICATIONS 2024; 13:95. [PMID: 38658541 PMCID: PMC11043335 DOI: 10.1038/s41377-024-01438-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2023] [Revised: 03/08/2024] [Accepted: 03/25/2024] [Indexed: 04/26/2024]
Abstract
The non-Hermitian skin effect describes the concentration of an extensive number of eigenstates near the boundaries of certain dissipative systems. This phenomenon has raised a huge interest in different areas of physics, including photonics, deeply expanding our understanding of non-Hermitian systems and opening up new avenues in both fundamental and applied aspects of topological phenomena. The skin effect has been associated to a nontrivial point-gap spectral topology and has been experimentally demonstrated in a variety of synthetic matter systems, including photonic lattices. In most of physical models exhibiting the non-Hermitian skin effect full or partial wave coherence is generally assumed. Here we push the concept of skin effect into the fully incoherent regime and show that rather generally (but not universally) the non-Hermitian skin effect persists under dephasing dynamics. The results are illustrated by considering incoherent light dynamics in non-Hermitian photonic quantum walks.
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Affiliation(s)
- Stefano Longhi
- Dipartimento di Fisica, Politecnico di Milano, Piazza L. da Vinci 32, I-20133, Milano, Italy.
- IFISC (UIB-CSIC), Instituto de Fisica Interdisciplinar y Sistemas Complejos, E-07122, Palma de Mallorca, Spain.
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3
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Zhang X, Wu C, Yan M, Liu N, Wang Z, Chen G. Observation of continuum Landau modes in non-Hermitian electric circuits. Nat Commun 2024; 15:1798. [PMID: 38413597 PMCID: PMC10899205 DOI: 10.1038/s41467-024-46122-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2023] [Accepted: 02/08/2024] [Indexed: 02/29/2024] Open
Abstract
Continuum Landau modes - predicted recently in a non-Hermitian Dirac Hamiltonian under a uniform magnetic field - are continuous bound states with no counterparts in Hermitian systems. However, they have still not been confirmed in experiments. Here, we report an experimental observation of continuum Landau modes in non-Hermitian electric circuits, in which the non-Hermitian Dirac Hamiltonian is simulated by non-reciprocal hoppings and the pseudomagnetic field is introduced by inhomogeneous complex on-site potentials. Through measuring the admittance spectrum and the eigenstates, we successfully verify key features of continuum Landau modes. Particularly, we observe the exotic voltage response acting as a rainbow trap or wave funnel through full-field excitation. This response originates from the linear relationship between the modes' center position and complex eigenvalues. Our work builds a bridge between non-Hermiticity and magnetic fields, and thus opens an avenue to explore exotic non-Hermitian physics.
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Affiliation(s)
- Xuewei Zhang
- School of Physics and Microelectronics, Key Laboratory of Materials Physics of Ministry of Education, Zhengzhou University, Zhengzhou, 450001, China
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser spectroscopy, Shanxi University, Taiyuan, 030006, China
| | - Chaohua Wu
- School of Physics and Microelectronics, Key Laboratory of Materials Physics of Ministry of Education, Zhengzhou University, Zhengzhou, 450001, China
| | - Mou Yan
- School of Physics and Microelectronics, Key Laboratory of Materials Physics of Ministry of Education, Zhengzhou University, Zhengzhou, 450001, China
- Institute of Quantum Materials and Physics, Henan Academy of Sciences, Zhengzhou, 450046, China
| | - Ni Liu
- Institute of Theoretical Physics, Shanxi University, Taiyuan, 030006, China
| | - Ziyu Wang
- The Institute of Technological Sciences, Wuhan University, Wuhan, 430072, China.
| | - Gang Chen
- School of Physics and Microelectronics, Key Laboratory of Materials Physics of Ministry of Education, Zhengzhou University, Zhengzhou, 450001, China.
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser spectroscopy, Shanxi University, Taiyuan, 030006, China.
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Bai K, Liu TR, Fang L, Li JZ, Lin C, Wan D, Xiao M. Observation of Nonlinear Exceptional Points with a Complete Basis in Dynamics. PHYSICAL REVIEW LETTERS 2024; 132:073802. [PMID: 38427883 DOI: 10.1103/physrevlett.132.073802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2023] [Accepted: 01/12/2024] [Indexed: 03/03/2024]
Abstract
The exotic physics associated with exceptional points (EPs) is always under the scrutiny of theoretical and experimental science. Recently, considerable effort has been invested in the combination of nonlinearity and non-Hermiticity. The concept of nonlinear EPs (NEPs) has been introduced, which can avoid the loss of completeness of the eigenbasis in dynamics while retaining the key features of linear EPs. Here, we present the first direct experimental demonstration of a NEP based on two non-Hermition coupled circuit resonators combined with a nonlinear saturable gain. At the NEP, the response of the eigenfrequency to perturbations demonstrates a third-order root law and the eigenbasis of the Hamiltonian governing the system dynamics is still complete. Our results bring this counterintuitive aspect of the NEP to light and possibly open new avenues for applications.
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Affiliation(s)
- Kai Bai
- Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072, China
| | - Tian-Rui Liu
- Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072, China
| | - Liang Fang
- Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072, China
| | - Jia-Zheng Li
- Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072, China
| | - Chen Lin
- Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072, China
| | - Duanduan Wan
- Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072, China
| | - Meng Xiao
- Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072, China
- Wuhan Institute of Quantum Technology, Wuhan 430206, China
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Rivero JDH, Fleming C, Qi B, Feng L, Ge L. Robust Zero Modes in Non-Hermitian Systems without Global Symmetries. PHYSICAL REVIEW LETTERS 2023; 131:223801. [PMID: 38101337 DOI: 10.1103/physrevlett.131.223801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2023] [Accepted: 11/02/2023] [Indexed: 12/17/2023]
Abstract
We present an approach to achieve zero modes in lattice models that do not rely on any symmetry or topology of the bulk, which are robust against disorder in the bulk of any type and strength. Such symmetry-free zero modes (SFZMs) are formed by attaching a single site or small cluster with zero mode(s) to the bulk, which serves as the "nucleus" that expands to the entire lattice. We identify the requirements on the couplings between this boundary and the bulk, which reveals that this approach is intrinsically non-Hermitian. We then provide several examples with either an arbitrary or structured bulk, forming spectrally embedded zero modes in the bulk continuum, midgap zero modes, and even restoring the "zeroness" of coupling or disorder-shifted topological corner states. Focusing on viable realizations using photonic lattices, we show that the resulting SFZM can be observed as the single lasing mode when optical gain is applied to the boundary.
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Affiliation(s)
- Jose D H Rivero
- College of Staten Island, CUNY, Staten Island, New York 10314, USA
- The Graduate Center, CUNY, New York, New York 10016, USA
| | - Courtney Fleming
- College of Staten Island, CUNY, Staten Island, New York 10314, USA
- The Graduate Center, CUNY, New York, New York 10016, USA
| | - Bingkun Qi
- College of Staten Island, CUNY, Staten Island, New York 10314, USA
- The Graduate Center, CUNY, New York, New York 10016, USA
| | - Liang Feng
- Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Li Ge
- College of Staten Island, CUNY, Staten Island, New York 10314, USA
- The Graduate Center, CUNY, New York, New York 10016, USA
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Wang X, Gu R, Li Y, Qi H, Hu X, Wang X, Gong Q. A scheme for realizing nonreciprocal interlayer coupling in bilayer topological systems. FRONTIERS OF OPTOELECTRONICS 2023; 16:38. [PMID: 38010425 PMCID: PMC10682335 DOI: 10.1007/s12200-023-00094-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/21/2023] [Accepted: 10/29/2023] [Indexed: 11/29/2023]
Abstract
Nonreciprocal interlayer coupling is difficult to practically implement in bilayer non-Hermitian topological photonic systems. In this work, we identify a similarity transformation between the Hamiltonians of systems with nonreciprocal interlayer coupling and on-site gain/loss. The similarity transformation is widely applicable, and we show its application in one- and two-dimensional bilayer topological systems as examples. The bilayer non-Hermitian system with nonreciprocal interlayer coupling, whose topological number can be defined using the gauge-smoothed Wilson loop, is topologically equivalent to the bilayer system with on-site gain/loss. We also show that the topological number of bilayer non-Hermitian C6v-typed domain-induced topological interface states can be defined in the same way as in the case of the bilayer non-Hermitian Su-Schrieffer-Heeger model. Our results show the relations between two microscopic provenances of the non-Hermiticity and provide a universal and convenient scheme for constructing and studying nonreciprocal interlayer coupling in bilayer non-Hermitian topological systems. This scheme is useful for observation of non-Hermitian skin effect in three-dimensional systems.
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Affiliation(s)
- Xiaoxiao Wang
- State Key Laboratory for Mesoscopic Physics and Department of Physics, Collaborative Innovation Center of Quantum Matter & Frontiers Science Center for Nano-Optoelectronics, Beijing Academy of Quantum Information Sciences, Peking University, Beijing, 100871, China
| | - Ruizhe Gu
- State Key Laboratory for Mesoscopic Physics and Department of Physics, Collaborative Innovation Center of Quantum Matter & Frontiers Science Center for Nano-Optoelectronics, Beijing Academy of Quantum Information Sciences, Peking University, Beijing, 100871, China
| | - Yandong Li
- State Key Laboratory for Mesoscopic Physics and Department of Physics, Collaborative Innovation Center of Quantum Matter & Frontiers Science Center for Nano-Optoelectronics, Beijing Academy of Quantum Information Sciences, Peking University, Beijing, 100871, China
| | - Huixin Qi
- State Key Laboratory for Mesoscopic Physics and Department of Physics, Collaborative Innovation Center of Quantum Matter & Frontiers Science Center for Nano-Optoelectronics, Beijing Academy of Quantum Information Sciences, Peking University, Beijing, 100871, China
| | - Xiaoyong Hu
- State Key Laboratory for Mesoscopic Physics and Department of Physics, Collaborative Innovation Center of Quantum Matter & Frontiers Science Center for Nano-Optoelectronics, Beijing Academy of Quantum Information Sciences, Peking University, Beijing, 100871, China.
- Peking University Yangtze Delta Institute of Optoelectronics, Nantong, 226010, China.
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, 030006, China.
- Hefei National Laboratory, Hefei, 230088, China.
| | - Xingyuan Wang
- College of Mathematics and Physics, Beijing University of Chemical Technology, Beijing, 100029, China.
| | - Qihuang Gong
- State Key Laboratory for Mesoscopic Physics and Department of Physics, Collaborative Innovation Center of Quantum Matter & Frontiers Science Center for Nano-Optoelectronics, Beijing Academy of Quantum Information Sciences, Peking University, Beijing, 100871, China
- Peking University Yangtze Delta Institute of Optoelectronics, Nantong, 226010, China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, 030006, China
- Hefei National Laboratory, Hefei, 230088, China
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