Article
Materials Science, Multidisciplinary
Yang Li, Xiang Ji, Yuanping Chen, Xiaohong Yan, Xiaosen Yang
Summary: In this study, we investigate the energy braiding of non-Bloch bands in non-Hermitian systems. We introduce a one-dimensional non-Hermitian tight-binding model and identify a generic class of topological non-Bloch bands generated by the non-Hermitian skin effect. We propose non-Bloch topological invariants based on the generalized Brillouin zone to characterize the topology of these bands.
Article
Multidisciplinary Sciences
Wei Wang, Xulong Wang, Guancong Ma
Summary: The non-Hermitian skin effect (NHSE) is utilized to reshape the wavefunctions of topological modes (TMs) by delocalizing them from the boundary. The in-gap TMs become completely extended and form robust extended modes, protected by bulk-band topology, even against local disorders. Experimental realization in different topological lattices demonstrates the deformation of TMs into various shapes.
Article
Multidisciplinary Sciences
Bolun Hu, Zhiwang Zhang, Haixiao Zhang, Liyang Zheng, Wei Xiong, Zichong Yue, Xiaoyu Wang, Jianyi Xu, Ying Cheng, Xiaojun Liu, Johan Christensen
Summary: The study focuses on the application of sound waves in non-Hermitian systems and the importance of topological insulators in sound and light guidance. By using carbon nanotube films for acoustic gain, a topological gallery insulator has been successfully constructed, allowing for amplified and focused sound at audible frequencies.
Article
Physics, Multidisciplinary
Annan Fan, Shi-Dong Liang
Summary: This study introduces a generalized local-global correspondence, discovering that the patterns of pseudo-boundary states in the complex energy plane mapped to the Brillouin zone exhibit topological invariants against parameter deformation. The approach is demonstrated using the non-Hermitian Chern insulator model, providing consistent topological phases and revealing novel topological invariants embedded within the phase diagram of the model.
FRONTIERS OF PHYSICS
(2022)
Article
Multidisciplinary Sciences
Bo Peng, Adrien Bouhon, Bartomeu Monserrat, Robert-Jan Slager
Summary: This study predicts the presence of multi-gap topologies and phase transitions in the phonon spectra of monolayer silicates, providing a clear experimental verification. This is significant for understanding and verifying the existence of multi-gap topologies.
NATURE COMMUNICATIONS
(2022)
Review
Materials Science, Multidisciplinary
Hadiseh Nasari, Georgios G. Pyrialakos, Demetrios N. Christodoulides, Mercedeh Khajavikhan
Summary: Recent years have seen a surge of research in topological photonics, driven by the prospect of topological protection against defects, disorder, and perturbations. This field initially emerged in fermionic systems within the framework of quantum mechanics, but the presence of non-Hermiticity in many natural and artificial settings raises questions about its impact on topological arrangements and the possibility of new topological phases in non-conservative and out of equilibrium systems. This article provides an overview of recent developments and ongoing efforts in this field, highlighting the interplay between topology and non-Hermiticity and its potential for new frontiers and applications in photonics.
OPTICAL MATERIALS EXPRESS
(2023)
Article
Multidisciplinary Sciences
Kai Wang, Avik Dutt, Ki Youl Yang, Casey C. Wojcik, Jelena Vuckovic, Shanhui Fan
Summary: The nontrivial topological features of non-Hermitian systems can be experimentally demonstrated and controlled by changing modulation waveforms. This topological winding allows for the synthesis and characterization of nontrivial phases in nonconservative systems.
Article
Materials Science, Multidisciplinary
C. Wang, X. R. Wang
Summary: In this study, we have discovered that under certain conditions, the chiral boundary states of higher-dimensional non-Hermitian topological insulators can be Hermitian with real eigenenergies. By constructing Hermitian chiral edge and hinge states, these boundary channels exhibit perfect transmission coefficients and are robust against disorders. Furthermore, non-Hermitian topological insulators can undergo a unique topological Anderson insulator transition.
Article
Multidisciplinary Sciences
Sebastian Weidemann, Mark Kremer, Stefano Longhi, Alexander Szameit
Summary: Phase transitions in non-Hermitian quasicrystals can be mutually interlinked, and the intertwinement of symmetry breaking, topology, and mobility phase transitions is observed in this study using photonic quantum walks.
Article
Multidisciplinary Sciences
Shiqi Xia, Dimitrios Kaltsas, Daohong Song, Ioannis Komis, Jingjun Xu, Alexander Szameit, Hrvoje Buljan, Konstantinos G. Makris, Zhigang Chen
Summary: The study established a nonlinear non-Hermitian topological platform for active tuning of PT symmetry and topological states, revealing the interaction between sensitivity close to exceptional points and the robustness of non-Hermitian topological states. The research provides opportunities for unconventional light manipulation and device applications through single-channel control of global PT symmetry and topology via local nonlinearity.
Review
Physics, Multidisciplinary
Rijia Lin, Tommy Tai, Linhu Li, Ching Hua Lee
Summary: This article reviews recent developments in the non-Hermitian skin effect (NHSE), particularly focusing on its interactions with topology. It starts with an introduction to the modified bulk-boundary correspondence, the synergy between NHSE and band topology in higher dimensions, and the associated topology on the complex energy plane. It then explores emerging topics such as non-Hermitian criticality, dynamical NHSE phenomena, and the manifestation of NHSE beyond linear non-interacting crystal lattices, including its interplay with quantum many-body interactions. Finally, it surveys recent demonstrations and experimental proposals of NHSE.
FRONTIERS OF PHYSICS
(2023)
Article
Physics, Condensed Matter
Gang-Feng Guo, Yan Wang, Xi-Xi Bao, Lei Tan
Summary: This study reveals a direct connection between the winding number calculated in the framework of the Bloch band theory and the number of edge states in the periodic driving non-Hermitian model. It also demonstrates that changes in the phase of the hopping amplitude can induce topological phase transitions. Moreover, the introduction of a purely imaginary hopping term leads to an extremely rich phase diagram, and even topological invariants can be selected from unlimited winding numbers when only considering the next-nearest neighbor hopping term.
JOURNAL OF PHYSICS-CONDENSED MATTER
(2022)
Article
Physics, Multidisciplinary
Y. Z. Han, J. S. Liu, C. S. Liu
Summary: In this study, the counterpart of the non-Hermitian SSH model was constructed to demonstrate the elimination of the non-Hermitian skin effect and the non-Hermitian Aharonov-Bohm effect under open boundary conditions. The transformation of non-Hermitian models and non-reciprocal hopping in the non-Hermitian SSH models were also discussed. Additionally, the disappearance of effective imaginary magnetic flux in the partner of the non-Hermitian SSH model was elaborated, leading to the analytical determination of topological invariants in conventional Brillouin zone.
NEW JOURNAL OF PHYSICS
(2021)
Article
Multidisciplinary Sciences
Quan Lin, Tianyu Li, Lei Xiao, Kunkun Wang, Wei Yi, Peng Xue
Summary: The authors experimentally observe a non-Hermitian topological Anderson insulator using photonic quantum walks, revealing the competition between Anderson localization induced by random disorder and the non-Hermitian skin effect. They investigate the impact of disorder and non-Hermiticity on the localization and topological properties of the system, and demonstrate the biorthogonal criticality of disorder-induced topological phase transitions.
NATURE COMMUNICATIONS
(2022)
Article
Materials Science, Multidisciplinary
Longwen Zhou, Yongjian Gu, Jiangbin Gong
Summary: This study introduces a dual scheme to characterize the topology of non-Hermitian Floquet systems using a piecewise quenched nonreciprocal Su-Schrieffer-Heeger model. It reveals experimentally accessible winding numbers under periodic boundary conditions and a Floquet version of the open boundary winding number. The results suggest that a dual characterization of non-Hermitian Floquet topological matter is necessary for further studies in nonequilibrium systems.
Editorial Material
Physics, Applied
Yubin Park, Shanhui Fan
APPLIED PHYSICS LETTERS
(2023)
Article
Nanoscience & Nanotechnology
Alok Ghanekar, Jiahui Wang, Cheng Guo, Shanhui Fan, Michelle L. Povinelli
Summary: We propose a nonreciprocal thermal emitter based on the dynamic modulation of graphene. By designing a graphene ribbon grating on a dielectric slab, high-quality resonances can be excited in the long-IR region. Upon modulation of the Fermi energy of graphene, asymmetric modal splitting results in large nonreciprocity, violating Kirchhoff's law of thermal radiation.
Article
Multidisciplinary Sciences
Aviv Karnieli, Shai Tsesses, Renwen Yu, Nicholas Rivera, Zhexin Zhao, Ady Arie, Shanhui Fan, Ido Kaminer
Summary: Strong coupling plays a vital role in light-matter systems and is essential for many quantum technologies. By shaping the free-electron wave packet, full control of highly connected multi-qubit systems with nanometric spatial resolution is achieved. We propose the use of free electrons as high-resolution quantum sensors for strongly coupled light-matter systems. Quantum interference of the free-electron wave packet enables a quantum-enhanced sensing protocol for the position and dipole orientation of a subnanometer emitter inside a cavity. Our results demonstrate the great versatility and applicability of quantum interactions between free electrons and strongly coupled cavities, relying on the unique properties of free electrons as strongly interacting flying qubits with miniscule dimensions.
Article
Optics
Jiahui Wang, Sean P. Rodrigues, Ercan M. Dede, Shanhui Fan
Summary: Coherent programmable integrated photonics circuits have great potential as specialized hardware accelerators for deep learning tasks. We designed an optical neural network based on microring resonators, which has advantages in terms of device footprint and energy efficiency. Tunable coupled double ring structures are used for linear multiplication layers, and modulated microring resonators are used for reconfigurable nonlinear activation components. Optimization algorithms are developed to train direct tuning parameters based on the transfer matrix method and automatic differentiation for all optical components.
Article
Physics, Multidisciplinary
Dali Cheng, Kai Wang, Shanhui Fan
Summary: Non-Abelian gauge fields for photons in the synthetic frequency dimension can be created using dynamically modulated ring resonators, with photon polarization as the spin basis for matrix-valued gauge fields. By measuring the steady-state photon amplitudes inside resonators, the band structures of the Harper-Hofstadter Hamiltonian can be revealed, demonstrating the signatures of the underlying non-Abelian gauge field. These findings open up opportunities for investigating novel topological phenomena in photonic systems.
PHYSICAL REVIEW LETTERS
(2023)
Article
Optics
Guangzhen Li, Luojia Wang, Rui Ye, Yuanlin Zheng, Da-Wei Wang, Xiong-Jun Liu, Avik Dutt, Luqi Yuan, Xianfeng Chen
Summary: Measuring topological invariants is important for characterizing topological phases, but it is believed that bulk band structures cannot directly provide these invariants. In this study, we experimentally extract the Zak phase from the bulk band structures of a synthetic Su-Schrieffer-Heeger (SSH) lattice in the frequency dimension. By controlling the coupling strengths between symmetric and antisymmetric supermodes of two bichromatically driven rings, we observe a clear contrast between the non-trivial and trivial topological phases in the transmission spectra. Our method can be extended to higher dimensions and may have future applications in optical communications.
LIGHT-SCIENCE & APPLICATIONS
(2023)
Article
Multidisciplinary Sciences
Aviv Karnieli, Shanhui Fan
Summary: This work proposes a new approach to realize the Jaynes-Cummings model using low-energy free electrons coupled to dielectric microcavities and demonstrates several quantum technologies enabled by this method. By utilizing quantum recoil, the emission of multiple consecutive photons can be inhibited through a large detuning, effectively converting the free electron into a few-level system coupled to the cavity mode. The approach enables the generation of single photons, photon pairs, and even a quantum SWAP gate between a photon and a free electron with unity efficiency and high fidelity. The quantum free electrons, tunable by their kinetic energy, serve as versatile emitters with engineerable emission wavelengths, paving the way for quantum interconnects between photonic platforms at different spectral regimes.
Review
Nanoscience & Nanotechnology
Aodong Li, Heng Wei, Michele Cotrufo, Weijin Chen, Sander Mann, Xiang Ni, Bingcong Xu, Jianfeng Chen, Jian Wang, Shanhui Fan, Cheng-Wei Qiu, Andrea Alu, Lin Chen
Summary: This Review discusses the latest theoretical progress related to exceptional points (EPs) in non-Hermitian physics and their implications for emerging technologies in nanophotonics. The authors highlight fundamental advances in various nanoscale systems and the theoretical progress in EPs, including higher-order EPs, bulk Fermi arcs, and Weyl exceptional rings. They also explore EP-associated emerging technologies and discuss the constraints and limitations of EP applications.
NATURE NANOTECHNOLOGY
(2023)
Article
Optics
Komron J. Shayegan, Souvik Biswas, Bo Zhao, Shanhui Fan, Harry A. Atwater
Summary: Researchers have found that in magneto-optic InAs, the application of an in-plane magnetic field modifies the permittivity tensor, leading to an enhanced spectral directional emissivity and decreased absorptivity, ultimately violating Kirchhoff's law of thermal radiation.
Article
Multidisciplinary Sciences
Lingling Fan, Kai Wang, Heming Wang, Avik Dutt, Shanhui Fan
Summary: Photonic convolution, a crucial operation in signal and image processing, can overcome computational bottlenecks and outperform electronic implementations. This study demonstrates the realization of convolution operations in the synthetic frequency dimension using a modulated ring resonator. By synthesizing arbitrary convolution kernels with high accuracy, we showcase the computation between input frequency combs and synthesized kernels. Our work highlights the efficient data encoding and computation capabilities of the synthetic frequency dimension, paving the way for compact and scalable photonic computation architecture.
Article
Multidisciplinary Sciences
Haoning Tang, Beicheng Lou, Fan Du, Mingjie Zhang, Xueqi Ni, Weijie Xu, Rebekah Jin, Shanhui Fan, Eric Mazur
Summary: Recently, twisted bilayer photonic materials have been widely used to create and study photonic tunability through interlayer couplings. However, measuring optical frequencies experimentally has been challenging. In this study, the first on-chip optical twisted bilayer photonic crystal with twist angle-tunable dispersion and good simulation-experiment agreement is demonstrated. The results reveal a highly tunable band structure of twisted bilayer photonic crystals due to moire scattering, opening up possibilities for unconventional twisted bilayer properties and novel applications in optical frequency regimes.
Article
Materials Science, Multidisciplinary
Mengqi Liu, Weijin Chen, Guangwei Hu, Shanhui Fan, Demetrios N. Christodoulides, Changying Zhao, Cheng-Wei Qiu
Summary: Perfect absorbers that can completely absorb all incoming energy have been extensively studied and found to be associated with topological spectral phase singularities (SPS). The order of the topological invariant depends on the number of degenerate outgoing channels. By examining mirror-backed and all-dielectric structures, the generation, evolution, and annihilation of SPSs with different orders are revealed. A strategy based on charge conservation of SPSs has been established to design dual-band perfect absorbers. These findings highlight the topological origin of perfect absorption and its potential applications in biosensing, topological metasurfaces, and micro/nano thermal radiation.
Article
Materials Science, Multidisciplinary
Yoichiro Tsurimaki, Renwen Yu, Shanhui Fan
Summary: In this paper, we study the thermodynamic performance of photonic heat engines and pumps based on fluctuating electromagnetic fields and relativistic thermodynamics. We find that the physical mechanisms behind the heat engine are the nonreciprocity and the Doppler effect. We also show that using nonreciprocal materials can help reduce the required velocity, and derive a relativistic version of thermodynamic efficiency that is bounded by the Carnot efficiency.
Review
Nanoscience & Nanotechnology
Xuhan Guo, Xingchen Ji, Baicheng Yao, Teng Tan, Allen Chu, Ohad Westreich, Avik Dutt, Cheewei Wong, Yikai Su
Summary: Silicon photonics has succeeded in realizing compact and low-cost devices, but it is not suitable for some emerging applications. To solve this issue, introducing wideband materials through heterogeneous integration on silicon substrates is desirable. This article discusses the properties of different materials and provides examples of devices using these materials on silicon platform. They also introduce a general fabrication method and low-loss process treatment for photonic devices. The potential applications in sensing, optical comb generation, and quantum information processing are highlighted. The article concludes by discussing the potential of new materials and integration methods for future widespread applications.
