The unique wave-manipulation capabilities of zero-index metamaterials(ZIMs)offer a new opportunity for realizing bound states in the continuum(BICs).However,the relationship between anomalous scattering and BICs remai...The unique wave-manipulation capabilities of zero-index metamaterials(ZIMs)offer a new opportunity for realizing bound states in the continuum(BICs).However,the relationship between anomalous scattering and BICs remains underexplored when parity–time(PT)symmetry is introduced.In this work,we demonstrate that a BIC splits into a pair of lasing modes carrying opposite topological charges by introducing PT symmetry through gain-loss cylinders embedded in ZIM layers.Theoretical analysis and numerical simulations reveal that lasing and unidirectional transparency phenomena result from the singularities and exceptional points of the scattering matrix.Moreover,exceptional points can be tuned via propagation phase modulation in the air gap,and their coalescence produces quasi-BICs with symmetric responses.This work provides a framework for manipulating BICs and topological lasing modes in non-Hermitian systems,offering new insights for designing non-Hermitian photonic devices.展开更多
We explore the parity-time(PT)-symmetry breaking transition in a dimer circuit composed of two RLC resonators that are weakly coupled via an inductor.The energy behavior of this dimer circuit is reflected in the split...We explore the parity-time(PT)-symmetry breaking transition in a dimer circuit composed of two RLC resonators that are weakly coupled via an inductor.The energy behavior of this dimer circuit is reflected in the splitting or degeneracy of the systems eigenfrequencies as the gain–loss strength varies.Its dynamical properties can be described by a non-Hermitian Hamiltonian.The eigenfrequency spectrum of the system is divided by two critical points into three distinct regions:the symmetric region,the oscillatory growth region,and the fully exponential growth region.Building upon previous work on implementing the exceptional point(EP)in circuit systems,our study focuses on further exploring the variation patterns of circuit eigenfrequencies near the EP under weak coupling conditions.In addition,we construct a corresponding Dirac point(DP)circuit system for comparison.By leveraging the unique physical properties near both the EP and the DP,we further propose potential practical applications.Using perturbation theory and system simulations,we demonstrate that the square-root eigenfrequency splitting near the EP significantly enhances the sensitivity to small external perturbations,compared to the linear splitting behavior near the DP.This study presents promising prospects for next-generation sensing technologies.展开更多
In this paper, we investigate the effect of exceptional points(EPs) on the violation of Leggett–Garg inequality(LGI) and no-signaling-in-time(NSIT) conditions and compare the different effects between the Hamiltonian...In this paper, we investigate the effect of exceptional points(EPs) on the violation of Leggett–Garg inequality(LGI) and no-signaling-in-time(NSIT) conditions and compare the different effects between the Hamiltonian EP(HEP) and Liouvillian EP(LEP) on those violations. We consider an open system consisting of two coupled qubits and each qubit is contacted with a thermal bath at a different temperature. In the case of omitting quantum jumps, we find that the system exhibits a second-order HEP, which separates the parameter space into an overdamped regime and an underdamped regime. In this situation, the LGI and NSIT conditions can be violated in both regimes and not violated at the HEP. In the case of without omitting quantum jumps, we find that the system exhibits a third-order LEP, which also separates the parameter space into an overdamped regime and an underdamped regime. In this situation, the LGI can only be violated in the underdamped regime with large coupling strength between the qubits.Conversely, the NSIT conditions can be violated in both regimes, as well as at the LEP, except in the overdamped regime with small coupling strength between the qubits. Comparing the violations of the LGI and NSIT conditions with HEP and LEP, we find that the quantum jumps would reduce the generation of coherence, enhance the decoherence, and lead to narrower parameter regimes that the LGI and NSIT conditions can be violated. Furthermore, in both cases,the NSIT conditions can be violated in a wider parameter regime than the LGI.展开更多
Elastic wave absorption at subwavelength scale is of significance in many engineering applications.Non-Hermitian metamaterials show the ability in high-efficiency wave absorption.However,the single functionality of me...Elastic wave absorption at subwavelength scale is of significance in many engineering applications.Non-Hermitian metamaterials show the ability in high-efficiency wave absorption.However,the single functionality of metamaterials is an important limitation on their practical applications for lack of tunability and reconfigurability.Here,we propose a tunable and reconfigurable non-Hermitian piezoelectric metamaterial bar,in which piezoelectric bars connect with resonant circuits,to achieve asymmetric unidirectional perfect absorption(UPA)and symmetric bidirectional perfect absorption(PA)at low frequencies.The two functions can be arbitrarily switched by rearranging shunted circuits.Based on the reverberation-ray matrix(RRM)method,an approach is provided to achieve UPA by setting an exceptional point(EP)in the coupled resonant bandgap.By using the transfer matrix method(TMM)and the finite element method(FEM),it is observed that a non-Hermitian pseudo-band forms between two resonant bandgaps,and the EP appears at the bottom of the pseudo-band.In addition,the genetic algorithm is used to accurately and efficiently design the shunted circuits for desired low-frequency UPA and PA.The present work may provide new strategies for vibration suppression and guided waves manipulation in wide potential applications.展开更多
Open physical systems described by the non-Hermitian Hamiltonian with parity-time-reversal(PT)symmetry show peculiar phenomena,such as the presence of an exceptional point(EP)at which the PT symmetry is broken and two...Open physical systems described by the non-Hermitian Hamiltonian with parity-time-reversal(PT)symmetry show peculiar phenomena,such as the presence of an exceptional point(EP)at which the PT symmetry is broken and two resonant modes of the Hamiltonian become degenerate.Near the EP,the system could be more sensitive to external perturbations and this may lead to enhanced sensing.In this paper,we present experimental results on the observation of PT symmetry broken transition and the EP using a tunable superconducting qubit.The quantum system of investigation is formed by the two levels of the qubit and the energy loss of the system to the environment is controlled by a method of parametric modulation of the qubit frequency.This method is simple with no requirements for additional elements or qubit device modifications.We believe it can be easily implemented on multi-qubit devices that would be suitable for further exploration of non-Hermitian physics in more complex and diverse systems.展开更多
We study the nonlinear perturbation of a high-order exceptional point(EP)of the order equal to the system site number L in a Hatano-Nelson model with unidirectional hopping and Kerr nonlinearity.Notably,we find a clas...We study the nonlinear perturbation of a high-order exceptional point(EP)of the order equal to the system site number L in a Hatano-Nelson model with unidirectional hopping and Kerr nonlinearity.Notably,we find a class of discrete breathers that aggregate to one boundary,here named as skin discrete breathers(SDBs).The nonlinear spectrum of these SDBs shows a hierarchical power-law scaling near the EP.Specifically,the response of nonlinear energy to the perturbation is given by E_(m)∝Γ~(α_(m)),whereα_(m)=3^(m-1)is the power with m=1,...,L labeling the nonlinear energy bands.This is in sharp contrast to the L-th root of a linear perturbation in general.These SDBs decay in a double-exponential manner,unlike the edge states or skin modes in linear systems,which decay exponentially.Furthermore,these SDBs can survive over the full range of nonlinearity strength and are continuously connected to the self-trapped states in the limit of large nonlinearity.They are also stable,as confirmed by a defined nonlinear fidelity of an adiabatic evolution from the stability analysis.As nonreciprocal nonlinear models may be experimentally realized in various platforms,such as the classical platform of optical waveguides,where Kerr nonlinearity is naturally present,and the quantum platform of optical lattices with Bose-Einstein condensates,our analytical results may inspire further exploration of the interplay between nonlinearity and non-Hermiticity,particularly on high-order EPs,and benchmark the relevant simulations.展开更多
The open quantum system can be described by either a Lindblad master equation or a non-Hermitian Hamiltonian(NHH).However,these two descriptions usually have different exceptional points(EPs),associated with the degen...The open quantum system can be described by either a Lindblad master equation or a non-Hermitian Hamiltonian(NHH).However,these two descriptions usually have different exceptional points(EPs),associated with the degeneracies in the open quantum system.Here,considering a dissipative quantum Rabi model,we study the spectral features of EPs in these two descriptions and explore their connections.We find that,although the EPs in these two descriptions are usually different,the EPs of NHH will be consistent with the EPs of master equation in the weak coupling regime.Further,we find that the quantum Fisher information(QFI),which measures the statistical distance between quantum states,can be used as a signature for the appearance of EPs.Our study may give a theoretical guidance for exploring the properties of EPs in open quantum systems.展开更多
We study the exceptional-point(EP) structure and the associated quantum dynamics in a system consisting of a non-Hermitian qubit and a Hermitian qubit. We find that the system possesses two sets of EPs, which divide t...We study the exceptional-point(EP) structure and the associated quantum dynamics in a system consisting of a non-Hermitian qubit and a Hermitian qubit. We find that the system possesses two sets of EPs, which divide the systemparameter space into PT-symmetry unbroken, partially broken and fully broken regimes, each with distinct quantumdynamics characteristics. Particularly, in the partially broken regime, while the PT-symmetry is generally broken in the whole four-dimensional Hilbert space, it is preserved in a two-dimensional subspace such that the quantum dynamics in the subspace are similar to those in the PT-symmetry unbroken regime. In addition, we reveal that the competition between the inter-qubit coupling and the intra-qubit driving gives rise to a complex pattern in the EP variation with system parameters.展开更多
The exceptional point（EP） is a significant and attractive phenomenon in an open quantum system. The scattering properties of light are similar to those in the open quantum system, which makes it possible to achieve ...The exceptional point（EP） is a significant and attractive phenomenon in an open quantum system. The scattering properties of light are similar to those in the open quantum system, which makes it possible to achieve EP in the optic system. Here we investigate the EP in a Fabry–P′erot（F–P） resonant coupling structure. The coupling between different types of F–P resonances leads to a near zero reflection, which results in a degeneration of eigenstates and thus the appearing of EP. Furthermore, the multi-wavelength EPs and unidirectional invisibility can be achieved which may be used in integrated photonics systems.展开更多
Recent breakthroughs in the field of non-Hermitian physics present unprecedented opportunities,from fundamental theories to cutting-edge applications such as multimode lasers,unconventional wave transport,and high-per...Recent breakthroughs in the field of non-Hermitian physics present unprecedented opportunities,from fundamental theories to cutting-edge applications such as multimode lasers,unconventional wave transport,and high-performance sensors.The exceptional point,a spectral singularity widely existing in non-Hermitian systems,provides an indispensable route to enhance the sensitivity of optical detection.However,the exceptional point of the forementioned systems is set once the system is built or fabricated,and machining errors make it hard to reach such a state precisely.To this end,we develop a highly tunable and reconfigurable exceptional point system,i.e.,a single spoof plasmonic resonator suspended above a substrate and coupled with two freestanding Rayleigh scatterers.Our design offers great flexibility to control exceptional point states,enabling us to dynamically reconfigure the exceptional point formed by various multipolar modes across a broadband frequency range.Specifically,we experimentally implement five distinct exceptional points by precisely manipulating the positions of two movable Rayleigh scatterers.In addition,the enhanced perturbation strength offers remarkable sensitivity enhancement for detecting deep-subwavelength particles with the minimum dimension down to 0.001λ(withλto be the free-space wavelength).展开更多
Degenerate states including exceptional points(EPs)and diabolic points(DPs)arise due to the underlying symmetry in physical systems.The interplay between different symmetry breakings opens a promising route for except...Degenerate states including exceptional points(EPs)and diabolic points(DPs)arise due to the underlying symmetry in physical systems.The interplay between different symmetry breakings opens a promising route for exceptional wave manipulation.Here,we conceptually demonstrate and experimentally prove that breaking parity symmetry and time-reversal symmetry through spatial perturbation and non-Hermitian perturbation,respectively,result in the evolution of EPs in pairs in a scattering system.These pairwise scattering EPs,which are orthogonal to each other and can be interconverted by mirror inversion,evolve continuously in the perturbation space and ultimately merge into a special non-Hermitian degenerate state—a non-Hermitian DP.The EPs and DP observed here exhibit distinct topological structures from different planes in the perturbation space,thus both carrying hybrid topological charges.Based on these findings,we show that metasurfaces at EPs can encode differences in scattering asymmetry,allowing for a complete yet arbitrary wave manipulation beyond previously reported non-Hermitian scattering metasurfaces.Our findings establish a general framework for exploring extreme wave scattering through combined-perturbation-driven degeneration evolution.展开更多
The strong connection between braids and knots provides valuable insights into studying the topological state and phase classification of various physical systems.The phenomenon of non-Hermitian(NH)two-and three-band ...The strong connection between braids and knots provides valuable insights into studying the topological state and phase classification of various physical systems.The phenomenon of non-Hermitian(NH)two-and three-band braiding has received widespread attention.However,a systematic exploration and visualization of non-Abelian braiding and the associated knot transformations in four-band systems remains unexplored.Here,we propose a theoretical model of NH four-band braiding,provide its phase diagram,and establish its trivial,Abelian,and non-Abelian braiding rules.Additionally,we report on special knots,such as the Hopf and Solomon links in braided knots,and reveal that their transformations are accompanied by and mediated through exceptional points.Our work provides a detailed case for studying NH multiband braiding and knot structures in four-band systems,which could offer insights for topological photonics and analog information processing applications.展开更多
Bound states in the continuum(BICs)and exceptional points(EPs),as two distinct physical singularities represented by complex frequencies in non-Hermitian systems,have garnered significant attention and clear definitio...Bound states in the continuum(BICs)and exceptional points(EPs),as two distinct physical singularities represented by complex frequencies in non-Hermitian systems,have garnered significant attention and clear definitions in their respective fields in recent years.They share overlapping applications in areas such as high-sensitivity sensing and laser emission.However,the transition between the two,inspired by these intersections,remains largely unexplored.In this work,we reveal the transition process in a non-Hermitian two-mode system,evolving from one bound singularity to a two-dimensional exceptional ring,where the EP is the coalescent state of the quasi-Friedrich-Wintgen(FW)-BIC.This phenomenon is experimentally validated through pored dielectric metasurfaces in terahertz band.Furthermore,external pumping induced photocarriers as the dissipative perturbation,facilitates the breaking of degeneracy in the complex eigenfrequency and enables dynamic EP switching.Finally,we experimentally demonstrate a switchable terahertz beam deflection driven by the phase singularities of the EP.These findings are instrumental in advancing the development of compact devices for sensing and wavefront control within non-Hermitian systems.展开更多
Exceptional points(EPs)have been extensively explored in mechanical,acoustic,plasmonic,and photonic systems.However,little is known about the role of EPs in tailoring the dynamic tunability of optical devices.A specif...Exceptional points(EPs)have been extensively explored in mechanical,acoustic,plasmonic,and photonic systems.However,little is known about the role of EPs in tailoring the dynamic tunability of optical devices.A specific type of EPs known as chiral EPs has recently attracted much attention for controlling the flow of light and for building sensors with better responsivity.A recently demonstrated route to chiral EPs via lithographically defined symmetric Mie scatterers on the rim of resonators has not only provided the much-needed mechanical stability for studying chiral EPs,but also helped reduce losses originating from nanofabrication imperfections,facilitating the in-situ study of chiral EPs and their contribution to the dynamics and tunability of resonators.Here,we use asymmetric Mie scatterers to break the rotational symmetry of a microresonator,to demonstrate deterministic thermal tuning across a chiral EP,and to demonstrate EP-mediated chiral optical nonlinear response and efficient electro-optic tuning.Our results indicate asymmetric electro-optic modulation with up to 17 dB contrast at GHz and CMOS-compatible voltage levels.Such wafer-scale nano-manufacturing of chiral electro-optic modulators and the chiral EP-tailored tunning may facilitate new micro-resonator functionalities in quantum information processing,electromagnetic wave control,and optical interconnects.展开更多
Classified as a non-Hermitian system,topological metasurface is one of the ideal platforms for exploring a striking property,that is,the exceptional point(EP).Recently,creating and encircling EP in metasurfaces has tr...Classified as a non-Hermitian system,topological metasurface is one of the ideal platforms for exploring a striking property,that is,the exceptional point(EP).Recently,creating and encircling EP in metasurfaces has triggered various progressive functionalities,including polarization control and optical holographic encoding.However,existing topological metasurfaces mostly rely on plasmonic materials,which introduce inevitable ohmic losses and limit their compatibility with mainstream all-dielectric meta-devices.Additionally,conventional free-space configurations also hinder the integration of multiple meta-devices in compact platforms.Here,an on-chip topological metasurface is experimentally demonstrated to create and engineer the topological phase encircling the EP in all-dielectric architecture.By massively screening the Si meta-atom geometry on the Si3N4 waveguide,a 2π-topological phase shift is obtained by encircling the EP.Through combining with the Pancharatnam-Berry(PB)phase,we decouple the orthogonal circular polarization channels and unfold the independent encoding freedom for different holographic generations.As a proof of concept,the proposed on-chip topological metasurface enables floating holographic visualizations in real-world scenarios,functioning as practical augmented reality(AR)functionalities.Such the all-dielectric on-chip scheme eliminates ohmic losses and enables compatible integration with other on-chip meta-devices,thus suggesting promising applications in next-generation AR devices,multiplexing information storage,and advanced optical displays.展开更多
Exceptional point(EP)is referred to degeneracies in a non-Hermitian system where two or more eigenvalues and their corresponding eigenvectors coalesce.Recently there have been significantly increased interests in harn...Exceptional point(EP)is referred to degeneracies in a non-Hermitian system where two or more eigenvalues and their corresponding eigenvectors coalesce.Recently there have been significantly increased interests in harnessing EPs to enhance responsivities and achieve ultrasensitive detections in optics,electronics and acoustics,although there are few similar studies focused on using surface acoustic wave(SAW)sensing technologies,probably due to its great technical challenges.Herein,we proposed a scheme for accessing EPs in an on-chip architecture consisted of coupledSAW-resonators system,forming a passive parity-time(PT)symmetric system.We demonstrated that by tuning additional losses in one of resonators and regulating the system in the proximity of the EP,the sensor exhibited significantly enhanced responses.As an example,we present an EP-based SAW gas sensor,which showed a muchimproved sensitivity compared to that of a conventional delay-line SAW sensor.The fundamental mechanisms behind this excellent sensing performance have been elucidated.展开更多
Point-of-care sensors are pivotal for early disease diagnosis,significantly advancing global health.Surface plasmons,the collective oscillations of free electrons under electromagnetic excitation,have been widely stud...Point-of-care sensors are pivotal for early disease diagnosis,significantly advancing global health.Surface plasmons,the collective oscillations of free electrons under electromagnetic excitation,have been widely studied for biosensing due to their electromagnetic field enhancements at sub-wavelength scales.We introduce a plasmonic biosensor on a compact photonic integrated circuit(PIC)enhanced by exceptional points(EPs).EPs,singularities in non-Hermitian optical systems,provide extreme sensitivity to external perturbations.They emerge when two or more complex resonating modes merge into a single degenerate mode.We demonstrate an EP in a single coupled nanoantenna particle positioned in a uniquely designed silicon nitride slot-waveguide,which we call a junction-waveguide.By laterally shifting two optically coupled gold nanobars of different lengths,we achieve a single particle EP.The junction-waveguide enables efficient coupling of the plasmonic nanoantenna to the waveguide mode.The system integrates a four-port Mach-Zehnder interferometer(MZI),allowing for simultaneous measurements of the amplitude and phase of EP,facilitating highly accurate real-time eigenvalue extraction.For biosensing,we encapsulated the detection zone with a microchannel,enabling low-volume and simple sample handling.Our single particle integrated EP sensor demonstrates superior sensitivity compared to the corresponding linear diabolic point(DP)system under both local and bulk sensing schemes,even at large perturbations.Our studies revealed that the integrated EP sensor can detect a single molecule captured by the nanobars with the average size ranging from 10 to 100 nm.The proposed EP biosensor,with its extreme sensitivity,compact form,and real-time phase sensing capabilities,provides an approach for detecting and quantifying various biomarkers such as proteins and nucleic acids,offering a unique platform for early disease diagnosis.展开更多
Non-Hermitian systems exhibit two unique hallmarks:exceptional points(EPs)and non-Hermitian skin effect(NHSE).The EP arises from the interplay of multiple energy levels,marked by degeneracy in eigenvalue spectra,while...Non-Hermitian systems exhibit two unique hallmarks:exceptional points(EPs)and non-Hermitian skin effect(NHSE).The EP arises from the interplay of multiple energy levels,marked by degeneracy in eigenvalue spectra,while the NHSE is associated with the localization feature of eigenfunctions.Due to their different origins and consequences,the interplay between the two hallmarks has drawn considerable interest.Here,we propose the concept of coupled NHSE,i.e.,two non-Hermitian systems with independent NHSE are coupled together.We find that by introducing non-Hermitian losses with special symmetry,multiple pairs of EPs can appear,greatly compressing the eigenvalue spectrum and accelerating the breakdown of the coupled NHSE.In contrast,the attenuation of coupled NHSE is significantly alleviated in systems without EPs.In this sense,the EP can act as a degree of freedom to tune the NHSE and govern the non-Hermitian dynamics.The proposed concept is experimentally realized in photonic lattices with artificial gauge fields,which will bridge these two significant concepts and open avenues for non-Hermitian applications simultaneously associated with them.展开更多
Linearly polarized(LP)modes are popular for fiber-optic communication systems,yet on-chip LP mode manipulation remains challenging.We propose a method for chiral switching of LP modes without encircling exceptional po...Linearly polarized(LP)modes are popular for fiber-optic communication systems,yet on-chip LP mode manipulation remains challenging.We propose a method for chiral switching of LP modes without encircling exceptional points in non-Hermitian systems.By adjusting one waveguide's radius and trajectory in a dual-coupled system,chiral LP mode switching is achieved,with output direction determined by the path.More importantly,the proposed device can simultaneously support two polarization states,which is highly significant for compatibility with polarization-division multiplexing systems.展开更多
Exceptional points(EPs)have extensive and important applications in many wave-based technologies,such as ultra-sensitive sensing,unidirectional scattering and low-threshold laser.However,most of the previous EP-relate...Exceptional points(EPs)have extensive and important applications in many wave-based technologies,such as ultra-sensitive sensing,unidirectional scattering and low-threshold laser.However,most of the previous EP-related wave phenomena are demonstrated in systems with fixed configuration,thereby extremely constraining their adaptability and reconfigurability in practice.Here,we introduce a flexible approach to tuning EPs in an acoustic system with sandwich structures.A rotatable component,associated with an alterable gradient index,is clamped by a pair of lossy acoustic resonators.Theoretical derivations and numerical simulations validate the capabilities of the model in continuously regulating EPs in the parameter space,with ingenious experimental setups confirming these findings.The results showcase the system's effectiveness in achieving unidirectional reflectionless wave propagation across various frequencies.Our research reveals a flexible approach to linking the adjustment of EPs to a simple structural parameter,offering a robust framework for exploring and implementing non-Hermitian wave phenomena in practical scenarios.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.12504361,12274313,and 62465005)the Natural Science Foundation of Guangxi(Grant No.2025GXNSFBA069179)the Guangxi Colleges and Universities Young and Middle-aged Teachers’Basic Scientific Research Ability Enhancement Project(Grant No.2025KY0093)。
文摘The unique wave-manipulation capabilities of zero-index metamaterials(ZIMs)offer a new opportunity for realizing bound states in the continuum(BICs).However,the relationship between anomalous scattering and BICs remains underexplored when parity–time(PT)symmetry is introduced.In this work,we demonstrate that a BIC splits into a pair of lasing modes carrying opposite topological charges by introducing PT symmetry through gain-loss cylinders embedded in ZIM layers.Theoretical analysis and numerical simulations reveal that lasing and unidirectional transparency phenomena result from the singularities and exceptional points of the scattering matrix.Moreover,exceptional points can be tuned via propagation phase modulation in the air gap,and their coalescence produces quasi-BICs with symmetric responses.This work provides a framework for manipulating BICs and topological lasing modes in non-Hermitian systems,offering new insights for designing non-Hermitian photonic devices.
基金the financial support of the Natural Science Foundation of Jiangsu Province(Grant No.BK20231320)。
文摘We explore the parity-time(PT)-symmetry breaking transition in a dimer circuit composed of two RLC resonators that are weakly coupled via an inductor.The energy behavior of this dimer circuit is reflected in the splitting or degeneracy of the systems eigenfrequencies as the gain–loss strength varies.Its dynamical properties can be described by a non-Hermitian Hamiltonian.The eigenfrequency spectrum of the system is divided by two critical points into three distinct regions:the symmetric region,the oscillatory growth region,and the fully exponential growth region.Building upon previous work on implementing the exceptional point(EP)in circuit systems,our study focuses on further exploring the variation patterns of circuit eigenfrequencies near the EP under weak coupling conditions.In addition,we construct a corresponding Dirac point(DP)circuit system for comparison.By leveraging the unique physical properties near both the EP and the DP,we further propose potential practical applications.Using perturbation theory and system simulations,we demonstrate that the square-root eigenfrequency splitting near the EP significantly enhances the sensitivity to small external perturbations,compared to the linear splitting behavior near the DP.This study presents promising prospects for next-generation sensing technologies.
基金financially supported by the National Natural Science Foundation of China (Grants Nos. 11775019 and 11875086)。
文摘In this paper, we investigate the effect of exceptional points(EPs) on the violation of Leggett–Garg inequality(LGI) and no-signaling-in-time(NSIT) conditions and compare the different effects between the Hamiltonian EP(HEP) and Liouvillian EP(LEP) on those violations. We consider an open system consisting of two coupled qubits and each qubit is contacted with a thermal bath at a different temperature. In the case of omitting quantum jumps, we find that the system exhibits a second-order HEP, which separates the parameter space into an overdamped regime and an underdamped regime. In this situation, the LGI and NSIT conditions can be violated in both regimes and not violated at the HEP. In the case of without omitting quantum jumps, we find that the system exhibits a third-order LEP, which also separates the parameter space into an overdamped regime and an underdamped regime. In this situation, the LGI can only be violated in the underdamped regime with large coupling strength between the qubits.Conversely, the NSIT conditions can be violated in both regimes, as well as at the LEP, except in the overdamped regime with small coupling strength between the qubits. Comparing the violations of the LGI and NSIT conditions with HEP and LEP, we find that the quantum jumps would reduce the generation of coherence, enhance the decoherence, and lead to narrower parameter regimes that the LGI and NSIT conditions can be violated. Furthermore, in both cases,the NSIT conditions can be violated in a wider parameter regime than the LGI.
基金the National Natural Science Foundation of China(Nos.11991033 and 11890681)。
文摘Elastic wave absorption at subwavelength scale is of significance in many engineering applications.Non-Hermitian metamaterials show the ability in high-efficiency wave absorption.However,the single functionality of metamaterials is an important limitation on their practical applications for lack of tunability and reconfigurability.Here,we propose a tunable and reconfigurable non-Hermitian piezoelectric metamaterial bar,in which piezoelectric bars connect with resonant circuits,to achieve asymmetric unidirectional perfect absorption(UPA)and symmetric bidirectional perfect absorption(PA)at low frequencies.The two functions can be arbitrarily switched by rearranging shunted circuits.Based on the reverberation-ray matrix(RRM)method,an approach is provided to achieve UPA by setting an exceptional point(EP)in the coupled resonant bandgap.By using the transfer matrix method(TMM)and the finite element method(FEM),it is observed that a non-Hermitian pseudo-band forms between two resonant bandgaps,and the EP appears at the bottom of the pseudo-band.In addition,the genetic algorithm is used to accurately and efficiently design the shunted circuits for desired low-frequency UPA and PA.The present work may provide new strategies for vibration suppression and guided waves manipulation in wide potential applications.
基金supported by the State Key Development Program for Basic Research of China(Grant Nos.2017YFA0304300 and 2016YFA0300600)the Key-Area Research and Development Program of Guangdong Province,China(Grant No.2020B0303030001)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB28000000).
文摘Open physical systems described by the non-Hermitian Hamiltonian with parity-time-reversal(PT)symmetry show peculiar phenomena,such as the presence of an exceptional point(EP)at which the PT symmetry is broken and two resonant modes of the Hamiltonian become degenerate.Near the EP,the system could be more sensitive to external perturbations and this may lead to enhanced sensing.In this paper,we present experimental results on the observation of PT symmetry broken transition and the EP using a tunable superconducting qubit.The quantum system of investigation is formed by the two levels of the qubit and the energy loss of the system to the environment is controlled by a method of parametric modulation of the qubit frequency.This method is simple with no requirements for additional elements or qubit device modifications.We believe it can be easily implemented on multi-qubit devices that would be suitable for further exploration of non-Hermitian physics in more complex and diverse systems.
基金Project supported by the National Key Research and Development Program of China(Grant No.2022YFA1405304)the Key-Area Research and Development Program of Guangdong Province,China(Grant No.2019B030330001)the Guangdong Provincial Key Laboratory(Grant No.2020B1212060066)。
文摘We study the nonlinear perturbation of a high-order exceptional point(EP)of the order equal to the system site number L in a Hatano-Nelson model with unidirectional hopping and Kerr nonlinearity.Notably,we find a class of discrete breathers that aggregate to one boundary,here named as skin discrete breathers(SDBs).The nonlinear spectrum of these SDBs shows a hierarchical power-law scaling near the EP.Specifically,the response of nonlinear energy to the perturbation is given by E_(m)∝Γ~(α_(m)),whereα_(m)=3^(m-1)is the power with m=1,...,L labeling the nonlinear energy bands.This is in sharp contrast to the L-th root of a linear perturbation in general.These SDBs decay in a double-exponential manner,unlike the edge states or skin modes in linear systems,which decay exponentially.Furthermore,these SDBs can survive over the full range of nonlinearity strength and are continuously connected to the self-trapped states in the limit of large nonlinearity.They are also stable,as confirmed by a defined nonlinear fidelity of an adiabatic evolution from the stability analysis.As nonreciprocal nonlinear models may be experimentally realized in various platforms,such as the classical platform of optical waveguides,where Kerr nonlinearity is naturally present,and the quantum platform of optical lattices with Bose-Einstein condensates,our analytical results may inspire further exploration of the interplay between nonlinearity and non-Hermiticity,particularly on high-order EPs,and benchmark the relevant simulations.
基金Project supported by the Key-Area Research and Development Program of GuangDong Province,China (Grant No. 2019B030330001)the National Natural Science Foundation of China (Grant Nos. 12025509, 11874434, and 11704420)+1 种基金the Science and Technology Program of Guangzhou (China)(Grant No. 201904020024)partially supported by the Guangzhou Science and Technology Projects (Grant No. 202002030459)
文摘The open quantum system can be described by either a Lindblad master equation or a non-Hermitian Hamiltonian(NHH).However,these two descriptions usually have different exceptional points(EPs),associated with the degeneracies in the open quantum system.Here,considering a dissipative quantum Rabi model,we study the spectral features of EPs in these two descriptions and explore their connections.We find that,although the EPs in these two descriptions are usually different,the EPs of NHH will be consistent with the EPs of master equation in the weak coupling regime.Further,we find that the quantum Fisher information(QFI),which measures the statistical distance between quantum states,can be used as a signature for the appearance of EPs.Our study may give a theoretical guidance for exploring the properties of EPs in open quantum systems.
基金partly funded by the Natural Science Foundation of Shandong Province of China (Grant Nos. ZR2021MA091 and ZR2018MA044)Introduction and Cultivation Plan of Youth Innovation Talents for Universities of Shandong Province (Research and Innovation Team on Materials Modification and Optoelectronic Devices at extreme conditions)。
文摘We study the exceptional-point(EP) structure and the associated quantum dynamics in a system consisting of a non-Hermitian qubit and a Hermitian qubit. We find that the system possesses two sets of EPs, which divide the systemparameter space into PT-symmetry unbroken, partially broken and fully broken regimes, each with distinct quantumdynamics characteristics. Particularly, in the partially broken regime, while the PT-symmetry is generally broken in the whole four-dimensional Hilbert space, it is preserved in a two-dimensional subspace such that the quantum dynamics in the subspace are similar to those in the PT-symmetry unbroken regime. In addition, we reveal that the competition between the inter-qubit coupling and the intra-qubit driving gives rise to a complex pattern in the EP variation with system parameters.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61377054 and 61675140)
文摘The exceptional point（EP） is a significant and attractive phenomenon in an open quantum system. The scattering properties of light are similar to those in the open quantum system, which makes it possible to achieve EP in the optic system. Here we investigate the EP in a Fabry–P′erot（F–P） resonant coupling structure. The coupling between different types of F–P resonances leads to a near zero reflection, which results in a degeneration of eigenstates and thus the appearing of EP. Furthermore, the multi-wavelength EPs and unidirectional invisibility can be achieved which may be used in integrated photonics systems.
基金supported by the National Natural Science Foundation of China(Grant Nos.61871215,61771238,and 61701246)the National Key Research and Development Program of China(Grant No.2022YFA1404903)+9 种基金the Fund of Qing Lan Project of Jiangsu Province(Grant No.1004-YQR22031)the Six Talent Peaks Project in Jiangsu Province(Grant No.2018-GDZB-009)the Fund of Prospective Layout of Scientific Research for NUAA(Nanjing University of Aeronautics and Astronautics)(Grant Nos.1004-ILA22002 and 1004-ILA22068)the Research and Practice Innovation Program of Nanjing University of Aeronautics and Astronautics(Grant No.xcxjh20210408)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.KYCX22_0364)the Fundamental Research Funds for the Central Universities,NUAA(Grant No.NS2023022)the Nanjing University of Aeronautics and Astronautics Startup Grant(Grant No.1004-YQR23031)the Distinguished Professor Fund of Jiangsu Province(Grant No.1004-YQR24010)Fundamental Research Funds for the Central Universities,NUAA(No.NE2024007)the Singapore National Research Foundation Competitive Research Program(NRF-CRP22-2019-0006).
文摘Recent breakthroughs in the field of non-Hermitian physics present unprecedented opportunities,from fundamental theories to cutting-edge applications such as multimode lasers,unconventional wave transport,and high-performance sensors.The exceptional point,a spectral singularity widely existing in non-Hermitian systems,provides an indispensable route to enhance the sensitivity of optical detection.However,the exceptional point of the forementioned systems is set once the system is built or fabricated,and machining errors make it hard to reach such a state precisely.To this end,we develop a highly tunable and reconfigurable exceptional point system,i.e.,a single spoof plasmonic resonator suspended above a substrate and coupled with two freestanding Rayleigh scatterers.Our design offers great flexibility to control exceptional point states,enabling us to dynamically reconfigure the exceptional point formed by various multipolar modes across a broadband frequency range.Specifically,we experimentally implement five distinct exceptional points by precisely manipulating the positions of two movable Rayleigh scatterers.In addition,the enhanced perturbation strength offers remarkable sensitivity enhancement for detecting deep-subwavelength particles with the minimum dimension down to 0.001λ(withλto be the free-space wavelength).
基金supported by the National Key R&D Program of China(Grant Nos.2022YFA1404400,and 2022 YFE0208000)the National Natural Science Foundation of China(Grant No.12474463)+3 种基金the Scientific Research Innovation Capability Support Project for Young Faculty(Grant No.ZYGXQNJSKYCXNLZCXM-D8)the Shanghai Pilot Program for Basic Researchthe Xiaomi Young Talents Programthe Fundamental Research Funds for the Central Universities。
文摘Degenerate states including exceptional points(EPs)and diabolic points(DPs)arise due to the underlying symmetry in physical systems.The interplay between different symmetry breakings opens a promising route for exceptional wave manipulation.Here,we conceptually demonstrate and experimentally prove that breaking parity symmetry and time-reversal symmetry through spatial perturbation and non-Hermitian perturbation,respectively,result in the evolution of EPs in pairs in a scattering system.These pairwise scattering EPs,which are orthogonal to each other and can be interconverted by mirror inversion,evolve continuously in the perturbation space and ultimately merge into a special non-Hermitian degenerate state—a non-Hermitian DP.The EPs and DP observed here exhibit distinct topological structures from different planes in the perturbation space,thus both carrying hybrid topological charges.Based on these findings,we show that metasurfaces at EPs can encode differences in scattering asymmetry,allowing for a complete yet arbitrary wave manipulation beyond previously reported non-Hermitian scattering metasurfaces.Our findings establish a general framework for exploring extreme wave scattering through combined-perturbation-driven degeneration evolution.
基金supported by the National Natural Science Foundation of China(Grant Nos.62575099,62075059,61405058)Guangdong Basic and Applied Basic Research Foundation(Grant No.2024A1515011353)+2 种基金Open Project of the State Key Laboratory of Advanced Optical Communication Systems and Networks of China(Grant No.2024GZKF20)the Natural Science Foundation of Hunan Province(Grant Nos.2020JJ4161 and 2017JJ2048)Scientific Research Foundation of Hunan Provincial Education Department(Grant No.21A0013)。
文摘The strong connection between braids and knots provides valuable insights into studying the topological state and phase classification of various physical systems.The phenomenon of non-Hermitian(NH)two-and three-band braiding has received widespread attention.However,a systematic exploration and visualization of non-Abelian braiding and the associated knot transformations in four-band systems remains unexplored.Here,we propose a theoretical model of NH four-band braiding,provide its phase diagram,and establish its trivial,Abelian,and non-Abelian braiding rules.Additionally,we report on special knots,such as the Hopf and Solomon links in braided knots,and reveal that their transformations are accompanied by and mediated through exceptional points.Our work provides a detailed case for studying NH multiband braiding and knot structures in four-band systems,which could offer insights for topological photonics and analog information processing applications.
基金supported by the National Nature Science Foundation of China(NSFC)(Nos.62222106,62288101,62027807,92163216,92463308,62071217,and 62275118)the Fundamental Research Funds for the Central Universities.
文摘Bound states in the continuum(BICs)and exceptional points(EPs),as two distinct physical singularities represented by complex frequencies in non-Hermitian systems,have garnered significant attention and clear definitions in their respective fields in recent years.They share overlapping applications in areas such as high-sensitivity sensing and laser emission.However,the transition between the two,inspired by these intersections,remains largely unexplored.In this work,we reveal the transition process in a non-Hermitian two-mode system,evolving from one bound singularity to a two-dimensional exceptional ring,where the EP is the coalescent state of the quasi-Friedrich-Wintgen(FW)-BIC.This phenomenon is experimentally validated through pored dielectric metasurfaces in terahertz band.Furthermore,external pumping induced photocarriers as the dissipative perturbation,facilitates the breaking of degeneracy in the complex eigenfrequency and enables dynamic EP switching.Finally,we experimentally demonstrate a switchable terahertz beam deflection driven by the phase singularities of the EP.These findings are instrumental in advancing the development of compact devices for sensing and wavefront control within non-Hermitian systems.
基金supported by the Defense Advanced Research Projects Agency(N660012114034)H.L.acknowledges the scholarship provided by the Republic of Korea Navy(ROK Nawy)+1 种基金The design and fabrication of the micro-heater and chiral MRR are supported by AFOSR(FA9550-18-1-0300)S.K.O.acknowledges the Air Force Offce of Scientific Research(AFOSR)Multi-University Research Initiative(FA9550-21-1-0202)and AFOSR(FA9550-18-1-0235)。
文摘Exceptional points(EPs)have been extensively explored in mechanical,acoustic,plasmonic,and photonic systems.However,little is known about the role of EPs in tailoring the dynamic tunability of optical devices.A specific type of EPs known as chiral EPs has recently attracted much attention for controlling the flow of light and for building sensors with better responsivity.A recently demonstrated route to chiral EPs via lithographically defined symmetric Mie scatterers on the rim of resonators has not only provided the much-needed mechanical stability for studying chiral EPs,but also helped reduce losses originating from nanofabrication imperfections,facilitating the in-situ study of chiral EPs and their contribution to the dynamics and tunability of resonators.Here,we use asymmetric Mie scatterers to break the rotational symmetry of a microresonator,to demonstrate deterministic thermal tuning across a chiral EP,and to demonstrate EP-mediated chiral optical nonlinear response and efficient electro-optic tuning.Our results indicate asymmetric electro-optic modulation with up to 17 dB contrast at GHz and CMOS-compatible voltage levels.Such wafer-scale nano-manufacturing of chiral electro-optic modulators and the chiral EP-tailored tunning may facilitate new micro-resonator functionalities in quantum information processing,electromagnetic wave control,and optical interconnects.
基金the National Key Research and Development Program of China(No.2022YFB3808600)the National Natural Science Foundation of China(No.12474391)+3 种基金the Fundamental Research Funds for the Central Universities(2042025kf0024)support from the National Natural Science Foundation of China(12474388)Guangdong Basic and Applied Basic Research Foundation(2025A1515011483)supported by the Center for NanoScience and Nanotechnology at Wuhan University.
文摘Classified as a non-Hermitian system,topological metasurface is one of the ideal platforms for exploring a striking property,that is,the exceptional point(EP).Recently,creating and encircling EP in metasurfaces has triggered various progressive functionalities,including polarization control and optical holographic encoding.However,existing topological metasurfaces mostly rely on plasmonic materials,which introduce inevitable ohmic losses and limit their compatibility with mainstream all-dielectric meta-devices.Additionally,conventional free-space configurations also hinder the integration of multiple meta-devices in compact platforms.Here,an on-chip topological metasurface is experimentally demonstrated to create and engineer the topological phase encircling the EP in all-dielectric architecture.By massively screening the Si meta-atom geometry on the Si3N4 waveguide,a 2π-topological phase shift is obtained by encircling the EP.Through combining with the Pancharatnam-Berry(PB)phase,we decouple the orthogonal circular polarization channels and unfold the independent encoding freedom for different holographic generations.As a proof of concept,the proposed on-chip topological metasurface enables floating holographic visualizations in real-world scenarios,functioning as practical augmented reality(AR)functionalities.Such the all-dielectric on-chip scheme eliminates ohmic losses and enables compatible integration with other on-chip meta-devices,thus suggesting promising applications in next-generation AR devices,multiplexing information storage,and advanced optical displays.
基金supported by National Key R&D Program of China under Grant 2022YFE0103300 and 2020YFA0211400.
文摘Exceptional point(EP)is referred to degeneracies in a non-Hermitian system where two or more eigenvalues and their corresponding eigenvectors coalesce.Recently there have been significantly increased interests in harnessing EPs to enhance responsivities and achieve ultrasensitive detections in optics,electronics and acoustics,although there are few similar studies focused on using surface acoustic wave(SAW)sensing technologies,probably due to its great technical challenges.Herein,we proposed a scheme for accessing EPs in an on-chip architecture consisted of coupledSAW-resonators system,forming a passive parity-time(PT)symmetric system.We demonstrated that by tuning additional losses in one of resonators and regulating the system in the proximity of the EP,the sensor exhibited significantly enhanced responses.As an example,we present an EP-based SAW gas sensor,which showed a muchimproved sensitivity compared to that of a conventional delay-line SAW sensor.The fundamental mechanisms behind this excellent sensing performance have been elucidated.
基金Army Research Office(W911NF2310027)NIH(S10OD034382)。
文摘Point-of-care sensors are pivotal for early disease diagnosis,significantly advancing global health.Surface plasmons,the collective oscillations of free electrons under electromagnetic excitation,have been widely studied for biosensing due to their electromagnetic field enhancements at sub-wavelength scales.We introduce a plasmonic biosensor on a compact photonic integrated circuit(PIC)enhanced by exceptional points(EPs).EPs,singularities in non-Hermitian optical systems,provide extreme sensitivity to external perturbations.They emerge when two or more complex resonating modes merge into a single degenerate mode.We demonstrate an EP in a single coupled nanoantenna particle positioned in a uniquely designed silicon nitride slot-waveguide,which we call a junction-waveguide.By laterally shifting two optically coupled gold nanobars of different lengths,we achieve a single particle EP.The junction-waveguide enables efficient coupling of the plasmonic nanoantenna to the waveguide mode.The system integrates a four-port Mach-Zehnder interferometer(MZI),allowing for simultaneous measurements of the amplitude and phase of EP,facilitating highly accurate real-time eigenvalue extraction.For biosensing,we encapsulated the detection zone with a microchannel,enabling low-volume and simple sample handling.Our single particle integrated EP sensor demonstrates superior sensitivity compared to the corresponding linear diabolic point(DP)system under both local and bulk sensing schemes,even at large perturbations.Our studies revealed that the integrated EP sensor can detect a single molecule captured by the nanobars with the average size ranging from 10 to 100 nm.The proposed EP biosensor,with its extreme sensitivity,compact form,and real-time phase sensing capabilities,provides an approach for detecting and quantifying various biomarkers such as proteins and nucleic acids,offering a unique platform for early disease diagnosis.
基金supported by National Key Research and Development Program of China(2024YFB4608100)the Young Top-Notch Talent for Ten Thousand Talent Program(X.L.Z.and Z.N.T.)+2 种基金National Natural Science Foundation of China(Grants No.12374350,No.61827826,No.62375103)the Major Science and Technology Projects in Jilin Province(20220301002GX)Innovation Program for Quantum Science and Technology(Grant No.2021ZD0300701).
文摘Non-Hermitian systems exhibit two unique hallmarks:exceptional points(EPs)and non-Hermitian skin effect(NHSE).The EP arises from the interplay of multiple energy levels,marked by degeneracy in eigenvalue spectra,while the NHSE is associated with the localization feature of eigenfunctions.Due to their different origins and consequences,the interplay between the two hallmarks has drawn considerable interest.Here,we propose the concept of coupled NHSE,i.e.,two non-Hermitian systems with independent NHSE are coupled together.We find that by introducing non-Hermitian losses with special symmetry,multiple pairs of EPs can appear,greatly compressing the eigenvalue spectrum and accelerating the breakdown of the coupled NHSE.In contrast,the attenuation of coupled NHSE is significantly alleviated in systems without EPs.In this sense,the EP can act as a degree of freedom to tune the NHSE and govern the non-Hermitian dynamics.The proposed concept is experimentally realized in photonic lattices with artificial gauge fields,which will bridge these two significant concepts and open avenues for non-Hermitian applications simultaneously associated with them.
基金supported by the National Natural Science Foundation of China(Nos.62125503 and 62261160388)the Natural Science Foundation of Hubei Province(No.2023AFA028)+3 种基金the Technology Innovation Program of Hubei Province(Major Science and Technology Project)(No.2024BAA001)the Hubei Optical Fundamental Research Center(No.HBO2025TQ004)the High Quality Development Special Project of the Ministry of Industry and Information Technologythe China Association for Science and Technology Youth Talent Support Engineering Doctoral Program。
文摘Linearly polarized(LP)modes are popular for fiber-optic communication systems,yet on-chip LP mode manipulation remains challenging.We propose a method for chiral switching of LP modes without encircling exceptional points in non-Hermitian systems.By adjusting one waveguide's radius and trajectory in a dual-coupled system,chiral LP mode switching is achieved,with output direction determined by the path.More importantly,the proposed device can simultaneously support two polarization states,which is highly significant for compatibility with polarization-division multiplexing systems.
基金supported by the National Natural Science Foundation of China(Grant Nos.92263208,12304494,and 12404534)the National Key R&D Program of China(Grant No.2022YFA1404400)+1 种基金the Open Fund of State Key Laboratory of Acoustics(Grant No.SKLA202313)the Fundamental Research Funds for the Central Universities。
文摘Exceptional points(EPs)have extensive and important applications in many wave-based technologies,such as ultra-sensitive sensing,unidirectional scattering and low-threshold laser.However,most of the previous EP-related wave phenomena are demonstrated in systems with fixed configuration,thereby extremely constraining their adaptability and reconfigurability in practice.Here,we introduce a flexible approach to tuning EPs in an acoustic system with sandwich structures.A rotatable component,associated with an alterable gradient index,is clamped by a pair of lossy acoustic resonators.Theoretical derivations and numerical simulations validate the capabilities of the model in continuously regulating EPs in the parameter space,with ingenious experimental setups confirming these findings.The results showcase the system's effectiveness in achieving unidirectional reflectionless wave propagation across various frequencies.Our research reveals a flexible approach to linking the adjustment of EPs to a simple structural parameter,offering a robust framework for exploring and implementing non-Hermitian wave phenomena in practical scenarios.
