Article
Physics, Fluids & Plasmas
Zheng-Yang Zhou, Ze-Liang Xiang, J. Q. You, Franco Nori
Summary: Studying the quantum thermodynamic properties of non-Hermitian systems presents challenges, but these can be addressed by modifying methods to ensure they maintain Hermitian properties. Calculating work statistics in non-Hermitian systems can represent a projection of statistics in a larger Hermitian system.
Article
Optics
Hyun Gyu Song, Minho Choi, Kie Young Woo, Chung Hyun Park, Yong-Hoon Cho
Summary: Researchers demonstrated room-temperature polaritonic parity-time-reversal symmetry by coupling exciton-polariton modes to one another in a six-fold symmetric microcavity with loss modulation. This direct coupling led to a phase transition from unbroken to broken symmetry, revealing the lowest threshold of polariton condensates in non-Hermitian degeneracies despite increasing loss.
Article
Nanoscience & Nanotechnology
Xianji Piao, Namkyoo Park
Summary: In this study, we demonstrate the existence of delocalization behaviors induced by non-Hermitian disorder in two-dimensional systems, as opposed to the typical disorder-induced localization. By controlling the contrast between material phases, we show a dramatic change in the relationship between localization and disorder, even exhibiting a disorder-induced delocalization in the low-contrast regime. This counterintuitive phenomenon originates from the disorder-induced clustering of non-Hermitian material phases, which leads to the unbroken condition of parity-time symmetry.
Article
Nanoscience & Nanotechnology
Tom A. W. Wolterink, Matthias Heinrich, Stefan Scheel, Alexander Szameit
Summary: This research experimentally verifies the invariant behavior of two-photon behavior under the reversal of order for concatenated two-mode linear optical transformations in photonic quantum networks. The results indicate new ways in which quantum correlations may be preserved in counterintuitive ways, even in small-scale non-Hermitian networks.
Article
Materials Science, Multidisciplinary
Qi-Bo Zeng
Summary: This work discusses the energy dependence of the non-Hermitian skin effect (NHSE) by introducing nonreciprocity beyond nearest-neighboring hopping in one-dimensional lattices. It is found that the direction of NHSE reverses as the eigenenergy of the system under open boundary conditions (OBCs) crosses critical energies. The concept of non-Hermitian skin effect edges, which separate the localized eigenstates at opposite ends of the lattice in the OBC spectrum, is introduced to characterize this phenomenon. The skin effect edges are determined by self-intersections in the spectrum under periodic boundary conditions (PBCs) and have topological properties.
Article
Optics
Dimitrios Chatzidimitriou, Alexandros Pitilakis, Traianos Yioultsis, Emmanouil E. Kriezis
Summary: The study explores the breaking of reciprocity in non-Hermitian coupled photonic waveguides through saturable absorption and the presence of exceptional points, providing important performance metrics for nonreciprocal operation of such devices with potential for high-speed applications.
Article
Optics
Qi-Bo Zeng, Rong Lu
Summary: We study a one-dimensional system subjected to a linearly varying imaginary vector potential. The eigenenergy spectrum is real under open boundary condition (OBC) but forms a parabola in the complex energy plane under periodic boundary condition (PBC). The eigenstates exhibit a modulated Gaussian distribution and are all pinned on the same position, determined by the imaginary vector potential and boundary conditions. These behaviors contrast with the non-Hermitian skin effect in systems with constant imaginary vector potential.
Article
Optics
Waqas Waseem Ahmed, Ramon Herrero, Muriel Botey, Ying Wu, Kestutis Staliunas
Summary: This study proposes a genetic algorithm-assisted inverse design approach to achieve 'on-demand' light transport in planar structures, with frequency-selective and broadband asymmetric reflectivity. By controlling the permittivity distribution, controllable unidirectional light reflection can be realized, offering new possibilities for frequency-selective one-way communication in integrated photonics.
Article
Optics
Hongbin Ma, Dongdong Li, Nanxuan Wu, Yiyun Zhang, Hongsheng Chen, Haoliang Qian
Summary: This research introduces the enhanced sensitivity around an exceptional point (EP) from parity-time (PT) symmetry theory into the design of nonlinear all-optical modulators. A non-Hermitian all-optical modulator based on PT symmetry is proposed, which utilizes the large Kerr nonlinearity from indium tin oxide (ITO) in its epsilon-near-zero (ENZ) region. This modulator operates around EP, offering advantages such as nanoscale integration and large modulation depth, and it can greatly contribute to the development of all-optical signal processing.
PHOTONICS RESEARCH
(2022)
Article
Materials Science, Multidisciplinary
Yidong Chong, Henry O. Everitt, Vincenzo Galdi, Mercedeh Khajavikhan, Gururaj V. Naik
Summary: This article is an introduction to the feature issue of Optical Materials Express on Non-Hermitian Optics and Photonics.
OPTICAL MATERIALS EXPRESS
(2023)
Article
Optics
J. Medina Pardell, R. Herrero, M. Botey, K. Staliunas
Summary: This study proposes a physical mechanism for stabilizing the complex spatiotemporal dynamics in arrays of broad area laser diodes by taking advantage of symmetry breaking in non-Hermitian potentials. Numerical analysis using a (2 + 1)-dimensional model shows regimes of temporal stabilization and light emission spatial redistribution and enhancement. The study also demonstrates a two-fold benefit with a simplified (1 + 1)-dimensional model for controlling temporal dynamics and enhancing output beam brightness through field concentration.
Article
Optics
Konrad Tschernig, Kurt Busch, Demetrios N. Christodoulides, Armando Perez-Leija
Summary: Exceptional points are complex-valued spectral singularities that can lead to loss-induced transparency, where system's overall loss can enhance transmission. The enhancements scale with the order of the exceptional points, making it interesting to devise strategies for high-order exceptional points. It is shown that high-order N-photon exceptional points can be generated by exciting non-Hermitian waveguide arrangements with coherent light states, allowing observation of N-photon enhanced loss-induced transparency in the quantum realm. Further analysis shows that number-resolved dynamics in nonconservative waveguide arrays can exhibit several exceptional points associated with different eigenmodes and dissipation rates.
LASER & PHOTONICS REVIEWS
(2022)
Review
Nanoscience & Nanotechnology
Midya Parto, Yuzhou G. N. Liu, Babak Bahari, Mercedeh Khajavikhan, Demetrios N. Christodoulides
Summary: In recent years, concepts from non-Hermitian physics have been successfully deployed in optics and other fields, leading to the discovery of counterintuitive phenomena. These ideas have extended to other areas in search of new behaviors and functionalities that would have been impossible in standard Hermitian arrangements.
Article
Materials Science, Multidisciplinary
Ken Mochizuki, Tomoki Ozawa
Summary: We investigate the band structures of one-dimensional open systems described by periodic non-Hermitian operators using continuum models and tight-binding models. Our results show that imaginary scalar potentials do not open band gaps but instead lead to the formation of exceptional points. Additionally, the bi-orthogonal tight-binding model successfully reproduces the dispersion relations of the continuum model.
Article
Optics
Jin Yan, Lifan Chen, Zhan Zheng, Jiajia Wei, Yaomin Jiang, Wenjing Zhao, Feng Li, Yanpeng Zhang, Yin Cai
Summary: In this study, we demonstrate the generation of multimode entanglement through atomic four-wave mixing and analyze the properties of exceptional points under dressing control in non-Hermitian systems. We achieve versatile exceptional points and higher-order exceptional points by leveraging dressing-controlled atomic nonlinearity. We also investigate the entanglement properties of various permutations of the output signal modes and show that non-Hermitian control allows for coherent multichannel control and extends the scale of quantum entanglement.
Article
Optics
Stefano Longhi
Summary: In non-Hermitian quasicrystals, the mobility edges (ME) that separate localized and extended states in the complex energy plane are of topological nature. The origin of non-Hermiticity determines the transport features, with different winding numbers corresponding to either ballistic transport or pseudo-dynamical localization.
Article
Optics
Stefano Longhi
Summary: In this study, a novel design for laser arrays is proposed, which achieves stable emission and strong suppression of supermode competition by tuning the complex frequencies of edge resonators. The design offers strong robustness and is applicable to systems with structural imperfections and dynamical instabilities.
Article
Physics, Multidisciplinary
Stefano Longhi
Summary: A unique feature of non-Hermitian systems is the skin effect, which refers to the edge localization of a considerable number of bulk-band eigenstates in a lattice with specific boundaries. Unlike Bloch waves in Hermitian systems, the skin modes in non-Hermitian systems are normalizable eigenstates originating from the intrinsic non-Hermitian point-gap topology of the Bloch band energy spectra. Additionally, these skin modes exhibit a fascinating property known as self-healing, where they can reconstruct their shape after being scattered by a space-time potential.
PHYSICAL REVIEW LETTERS
(2022)
Article
Multidisciplinary Sciences
Stefano Longhi
Summary: Non-Hermitian quasi-edge modes are exponentially localized states in systems with non-Hermitian skin effect. By tailoring on-site potentials at the edges of a finite lattice, selective and tunable excitation of topological quasi-edge states can be achieved.
PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES
(2022)
Article
Physics, Multidisciplinary
Stefano Longhi
Summary: The Hartman effect refers to the phenomenon that the time taken for a quantum mechanical particle or photon to tunnel through an opaque potential barrier becomes independent of the barrier width for long barriers. It has been observed in various physical settings and sparked debates and controversies regarding the definition and interpretation of tunneling times and the apparent superluminal transmission. This study investigates whether the Hartman effect persists in non-Hermitian barriers under conditions of inelastic scattering.
ANNALEN DER PHYSIK
(2022)
Article
Optics
Stefano Longhi
Summary: Discrete-time photonic quantum walks provide a platform for observing non-Hermitian physical phenomena and controlling light scattering. This study shows that slowly drifting Kramers-Kronig potentials can behave as invisible potentials in discrete-time photonic quantum walks.
Article
Optics
Stefano Longhi
Summary: Bloch-Zener oscillations, the interplay between Bloch oscillations and Zener tunneling in two-band lattices, are ubiquitous in wave physics. In non-Hermitian lattices, these oscillations can transition from aperiodic to periodic, and the phase transition can be either smooth or sharp, unlike other non-Hermitian phase transitions.
Article
Physics, Multidisciplinary
Hang Li, Zhaoli Dong, Stefano Longhi, Qian Liang, Dizhou Xie, Bo Yan
Summary: Aharonov-Bohm (AB) caging is a special flat-band localization mechanism that has attracted great interest in the study of quantum transport in flatband systems. This system exhibits unique behavior due to the interplay between geometric frustration, disorder, and correlations.
PHYSICAL REVIEW LETTERS
(2022)
Article
Physics, Multidisciplinary
Stefano Longhi
Summary: Anderson localization predicts that wave spreading in disordered lattices can stop completely, providing a universal mechanism for dynamical localization. In the one-dimensional Hermitian Anderson model, there is a correspondence between dynamical and spectral localization. However, this correspondence may be broken in disordered dissipative lattices.
ANNALEN DER PHYSIK
(2023)
Article
Optics
Stefano Longhi
Summary: Anderson localization is a common phenomenon in wavy systems that have strong static and uncorrelated disorder. However, in one-dimensional lattices with off diagonal disorder, Anderson localization can persist for arbitrary time-dependent drivings that do not break a hidden conservation law originating from the chiral symmetry, leading to the dubbed localization without eigenstates.
Article
Multidisciplinary Sciences
Shulin Wang, Chengzhi Qin, Lange Zhao, Han Ye, Stefano Longhi, Peixiang Lu, Bing Wang
Summary: This paper introduces a new class of reconfigurable linear optics circuits harnessing Floquet LZT, which has versatile applications in temporal beam control, signal processing, quantum simulations, and information processing.
Article
Physics, Multidisciplinary
Ermanno Pinotti, Stefano Longhi
Summary: A quantum particle constrained between two high potential barriers can exhibit quasi-bound states. The decay of the wave function in such states can be accelerated by additional lateral barriers, contrary to intuition. This acceleration is due to resonant tunneling effects and results in deviations from exponential decay.
Article
Optics
Stefano Longhi
Summary: This article discusses the differences in particle behavior in unbounded potentials between classical mechanics and wave mechanics, and introduces a new class of unbounded potentials where wave delocalization is observed. Experimental verification of this phenomenon is done through light dynamics in synthetic photonic lattices.
Article
Materials Science, Multidisciplinary
Stefano Longhi
Summary: We investigate the energy spectral phase transitions in one-dimensional superlattices with M sites and an imaginary gauge field. It is found that in models with nearly flat bands, a smooth phase transition from real to complex energies can be observed as the imaginary gauge field increases, becoming sharper with increasing M. This phase transition can be observed even in superlattices without disorder. These predicted phenomena can be realized in non-Hermitian photonic quantum walks using existing experimental apparatus.
Article
Materials Science, Multidisciplinary
Stefano Longhi, Liang Feng
Summary: In many classical and quantum systems with a non-Hermitian Hamiltonian, a spectral phase transition can occur when a non-Hermitian parameter exceeds a critical value, leading to a transition from a completely real-energy spectrum to a complex spectrum. The phenomenon is particularly evident in systems with parity-time (PT) symmetry, where the energy spectrum is real in the unbroken PT phase and becomes complex in the broken PT phase. However, when the system is cyclically and slowly cycled, the phase transition can become imperfect due to the complex Berry phase associated with the adiabatic evolution of the system.
