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
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
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
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
Exceptional points(EPs),which are typically defined as the degener-acy points of a non-Hermitian Hamiltonian,have been investigated in various physical systems such as photonic systems.In particular,the intriguing top...Exceptional points(EPs),which are typically defined as the degener-acy points of a non-Hermitian Hamiltonian,have been investigated in various physical systems such as photonic systems.In particular,the intriguing topological structures around EPs have given rise to novel strategies for manipulating photons and the underlying mechanism is especially useful for on-chip photonic applications.Although some on-chip experiments with the adoption of lasers have been reported,EP-based photonic chips working in the quantum regime largely re-main elusive.In the current work,a single-photon experiment was proposed to dynamically encircle an EP in on-chip photonic waveg-uides possessing passive anti-parity-time symmetry.Photon coinci-dences measurement reveals a chiral feature of transporting single photons,which can act as a building block for on-chip quantum de-vices that require asymmetric transmissions.The findings in the cur-rent work pave the way for on-chip experimental study on the physics of EPs as well as inspiring applications for on-chip non-Hermitian quantum devices.展开更多
Spontaneous symmetry breaking has revolutionized the understanding in numerous fields of modern physics. Here, we theoretically demonstrate the spontaneous time-reversal symmetry breaking in a cavity quantum electrody...Spontaneous symmetry breaking has revolutionized the understanding in numerous fields of modern physics. Here, we theoretically demonstrate the spontaneous time-reversal symmetry breaking in a cavity quantum electrodynamics system in which an atomic ensemble interacts coherently with a single resonant cavity mode. The interacting system can be effectively described by two coupled oscillators with positive and negative mass, when the two-level atoms are prepared in their excited states. The occurrence of symmetry breaking is controlled by the atomic detuning and the coupling to the cavity mode,which naturally divides the parameter space into the symmetry broken and symmetry unbroken phases.The two phases are separated by a spectral singularity, a so-called exceptional point, where the eigenstates of the Hamiltonian coalesce. When encircling the singularity in the parameter space, the quasiadiabatic dynamics shows chiral mode switching which enables topological manipulation of quantum states.展开更多
Non-orthogonality in non-Hermitian quantum systems gives rise to tremendous exotic quantum phenomena,which can be fundamentally traced back to non-unitarity.In this paper,we introduce an interesting quantity(denoted a...Non-orthogonality in non-Hermitian quantum systems gives rise to tremendous exotic quantum phenomena,which can be fundamentally traced back to non-unitarity.In this paper,we introduce an interesting quantity(denoted asη)as a new variant of the Petermann factor to directly and efficiently measure non-unitarity and the associated non-Hermitian physics.By tuning the model parameters of underlying non-Hermitian systems,we find that the discontinuity of bothηand its first-order derivative(denoted as■η)pronouncedly captures rich physics that is fundamentally caused by non-unitarity.More concretely,in the 1D non-Hermitian topological systems,two mutually orthogonal edge states that are respectively localized on two boundaries become non-orthogonal in the vicinity of discontinuity ofηas a function of the model parameter,which is dubbed"edge state transition".Through theoretical analysis,we identify that the appearance of edge state transition indicates the existence of exceptional points(EPs)in topological edge states.Regarding the discontinuity of■η,we investigate a two-level non-Hermitian model and establish a connection between the points of discontinuity of■ηand EPs of bulk states.By studying this connection in more general lattice models,we find that some models have discontinuity of■η,implying the existence of EPs in bulk states.展开更多
Topological phases featuring non-Abelian charges have garnered significant attention in recent years.In parallel,the study of multiband exceptional topology in non-Hermitian systems has emerged as a prominent research...Topological phases featuring non-Abelian charges have garnered significant attention in recent years.In parallel,the study of multiband exceptional topology in non-Hermitian systems has emerged as a prominent research direction.In this study,we investigate a parity-time(PT)symmetric Hamiltonian,which hosts both conventional non-Abelian topological phases(NATPs)and hybrid phases.We propose an experimental scheme using spin-1 atoms with spin-orbit coupling trapped in two-dimensional(2D)lattices.Before adding a non-Hermitian term,we find the emergence of distinct topological phases mixed by two NATPs and establish their connection with NATPs theory.When a non-Hermitian term that preserves PT symmetry protection was introduced,stable second-order exceptional rings and third-order exceptional points emerge and they drive the edge states to manifest as discontinuous Fermi arcs in the surface Brillouin zone.However,with the variation of the non-Hermitian term,it is rather intriguing that two types of exceptional rings here transition from being internally tangent to externally tangent,transforming into a new topological phase equivalent to the Hermitian case.This research provides deeper insights into the nature of NATPs and the topological implications of exceptional structures,contributing to the field of topological physics.展开更多
It is found that when the parity–time symmetry phenomenon is introduced into the resonant optical gyro system and it works near the exceptional point,the sensitivity can in theory be significantly amplified at low an...It is found that when the parity–time symmetry phenomenon is introduced into the resonant optical gyro system and it works near the exceptional point,the sensitivity can in theory be significantly amplified at low angular rate.However,in fact,the exceptional point is easily disturbed by external environmental variables,which means that it depends on harsh experimental environment and strong control ability,so it is difficult to move towards practical application.Here,we propose a new angular rate sensor structure based on exceptional surface,which has the advantages of high sensitivity and high robustness.The system consists of two fiber-optic ring resonators and two optical loop mirrors,and one of the resonators contains a variable ratio coupler and a variable optical attenuator.We theoretically analyze the system response,and the effects of phase and coupling ratio on the system response.Finally,compared with the conventional resonant gyro,the sensitivity of this exceptional surface angular rate sensor can be improved by about 300 times at low speed.In addition,by changing the loss coefficient in the ring resonator,we can achieve a wide range of 600 rad/s.This scheme provides a new approach for the development of ultra-high sensitivity and wide range angular rate sensors in the future.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
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
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
Transformation acoustics(TA)has emerged as a powerful tool for designing several intriguing conceptual devices,which can manipulate acoustic waves in a flexible manner,yet their applications are limited in Hermitian m...Transformation acoustics(TA)has emerged as a powerful tool for designing several intriguing conceptual devices,which can manipulate acoustic waves in a flexible manner,yet their applications are limited in Hermitian materials.In this work,we propose the theory of complex-coordinate transformation acoustics(CCTA)and verify the effectiveness in realizing acoustic non-Hermitian metamaterials.Especially,we apply this theory for the first time to the design of acoustic parity-time(PT)and antisymmetric parity-time(APT)metamaterials and demonstrate two distinctive examples.First,we use this method to obtain the exceptional points(EPs)of the PT/APT system and observe the spontaneous phase transition of the scattering matrix in the transformation parameter space.Second,by selecting the Jacobian matrix's constitutive parameters,the PT/APT-symmetric system can also be configured to approach the zero and pole of the scattering matrix,behaving as an acoustic coherent perfect absorber and equivalent laser.We envision our proposed CCTAbased paradigm to open the way for exploring the non-Hermitian physics and finding application in the design of acoustic functional devices such as absorbers and amplifiers whose material parameters are hard to realize by using the conventional transformation method.展开更多
Entanglement scaling behavior provides an established diag-nostic for critical phase transitions.Deeply rooted in boundary conformal field theory[1],it associates logarithmic entanglement entropy scalinglog L with 1D ...Entanglement scaling behavior provides an established diag-nostic for critical phase transitions.Deeply rooted in boundary conformal field theory[1],it associates logarithmic entanglement entropy scalinglog L with 1D criticality[2,3].Recently,such scaling behavior has been challenged in non-Hermitian systems:at exceptional points(EPs)[4],geometric defectiveness and proba-bility non-conservation lead to anomalous negative entanglement entropy in free-fermion systems[5],corresponding to a negative central charge as described by nonunitary conformal field theory[6].Despite these complications,all known non-Hermitian free-fermion critical systems still exhibit the celebratedL scaling.展开更多
Non-Hermitian systems can exhibit unconventional spectral singularities called exceptional points(EPs).Various EP sensors have been fabricated in recent years,showing strong spectral responses to external signals.Here...Non-Hermitian systems can exhibit unconventional spectral singularities called exceptional points(EPs).Various EP sensors have been fabricated in recent years,showing strong spectral responses to external signals.Here we propose how to achieve a nonlinear anti-parity-time(PT)gyroscope by spinning an optical resonator.We show that,in the absence of any nonlinearity,the sensitivity or optical mode splitting of the linear device can be magnified up to 3 orders compared to that of the conventional device without EPs.Remarkably,the PT symmetry can be broken when including the Kerr nonlinearity of the materials and,as a result,the detection threshold can be significantly lowered,i.e.,much weaker rotations which are well beyond the ability of a linear gyroscope can now be detected with the nonlinear device.Our work shows the powerful ability of PT gyroscopes in practice to achieve ultrasensitive rotation measurement.展开更多
We demonstrate the possibility of dual-band unidirectional reflectionlessness in a non-Hermitian quantum system composed of a plasmonic waveguide and two end-coupled plasmonic cavities(PCs).Our scheme exhibits dual-ba...We demonstrate the possibility of dual-band unidirectional reflectionlessness in a non-Hermitian quantum system composed of a plasmonic waveguide and two end-coupled plasmonic cavities(PCs).Our scheme exhibits dual-band unidirectional reflectionlessness can be obtained at exceptional points by properly adjusting the coupling strength between two PCs,the ratio of decay rates of two PCs,and the ratio of plasmonic cavity-waveguide coupling strengths.As a valuable feature,the quality factor reaches to~175.4 in forward direction,while the backward quality factor is close to~188.2.展开更多
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 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.
基金supported by National Natural Sci-ence Foundation of China(NSFC)under Grants 61825502,11974140 and#61827826Scientific and Technological Development Plan Program of Jilin Province(SKL202302012)Work done in Hong Kong was supported by RGC Hong Kong(N_HKUST608/17,AoE/P-502/20 and C6013-18G-A)and by the Croucher Foundation.
文摘Exceptional points(EPs),which are typically defined as the degener-acy points of a non-Hermitian Hamiltonian,have been investigated in various physical systems such as photonic systems.In particular,the intriguing topological structures around EPs have given rise to novel strategies for manipulating photons and the underlying mechanism is especially useful for on-chip photonic applications.Although some on-chip experiments with the adoption of lasers have been reported,EP-based photonic chips working in the quantum regime largely re-main elusive.In the current work,a single-photon experiment was proposed to dynamically encircle an EP in on-chip photonic waveg-uides possessing passive anti-parity-time symmetry.Photon coinci-dences measurement reveals a chiral feature of transporting single photons,which can act as a building block for on-chip quantum de-vices that require asymmetric transmissions.The findings in the cur-rent work pave the way for on-chip experimental study on the physics of EPs as well as inspiring applications for on-chip non-Hermitian quantum devices.
基金supported by the National Key R&D Program of China(2016YFA0301302)the National Natural Science Foundation of China(61435001,11654003,11474011)High-performance Computing Platform of Peking University
文摘Spontaneous symmetry breaking has revolutionized the understanding in numerous fields of modern physics. Here, we theoretically demonstrate the spontaneous time-reversal symmetry breaking in a cavity quantum electrodynamics system in which an atomic ensemble interacts coherently with a single resonant cavity mode. The interacting system can be effectively described by two coupled oscillators with positive and negative mass, when the two-level atoms are prepared in their excited states. The occurrence of symmetry breaking is controlled by the atomic detuning and the coupling to the cavity mode,which naturally divides the parameter space into the symmetry broken and symmetry unbroken phases.The two phases are separated by a spectral singularity, a so-called exceptional point, where the eigenstates of the Hamiltonian coalesce. When encircling the singularity in the parameter space, the quasiadiabatic dynamics shows chiral mode switching which enables topological manipulation of quantum states.
基金supported by the National Natural Science Foundation of China(NSFC)Grant No.12074438the Guangdong Basic and Applied Basic Research Foundation under Grant No.2020B1515120100+1 种基金the Open Project of Guangdong Provincial Key Laboratory of Magnetoelectric Physics and Devices under Grant No.2022B1212010008the Fundamental Research Funds for the Central Universities,Sun Yat-sen University(No.23ptpy05).
文摘Non-orthogonality in non-Hermitian quantum systems gives rise to tremendous exotic quantum phenomena,which can be fundamentally traced back to non-unitarity.In this paper,we introduce an interesting quantity(denoted asη)as a new variant of the Petermann factor to directly and efficiently measure non-unitarity and the associated non-Hermitian physics.By tuning the model parameters of underlying non-Hermitian systems,we find that the discontinuity of bothηand its first-order derivative(denoted as■η)pronouncedly captures rich physics that is fundamentally caused by non-unitarity.More concretely,in the 1D non-Hermitian topological systems,two mutually orthogonal edge states that are respectively localized on two boundaries become non-orthogonal in the vicinity of discontinuity ofηas a function of the model parameter,which is dubbed"edge state transition".Through theoretical analysis,we identify that the appearance of edge state transition indicates the existence of exceptional points(EPs)in topological edge states.Regarding the discontinuity of■η,we investigate a two-level non-Hermitian model and establish a connection between the points of discontinuity of■ηand EPs of bulk states.By studying this connection in more general lattice models,we find that some models have discontinuity of■η,implying the existence of EPs in bulk states.
基金supported by the National Natural Science Foundation of China(Grant Nos.12274473 and 12135018).
文摘Topological phases featuring non-Abelian charges have garnered significant attention in recent years.In parallel,the study of multiband exceptional topology in non-Hermitian systems has emerged as a prominent research direction.In this study,we investigate a parity-time(PT)symmetric Hamiltonian,which hosts both conventional non-Abelian topological phases(NATPs)and hybrid phases.We propose an experimental scheme using spin-1 atoms with spin-orbit coupling trapped in two-dimensional(2D)lattices.Before adding a non-Hermitian term,we find the emergence of distinct topological phases mixed by two NATPs and establish their connection with NATPs theory.When a non-Hermitian term that preserves PT symmetry protection was introduced,stable second-order exceptional rings and third-order exceptional points emerge and they drive the edge states to manifest as discontinuous Fermi arcs in the surface Brillouin zone.However,with the variation of the non-Hermitian term,it is rather intriguing that two types of exceptional rings here transition from being internally tangent to externally tangent,transforming into a new topological phase equivalent to the Hermitian case.This research provides deeper insights into the nature of NATPs and the topological implications of exceptional structures,contributing to the field of topological physics.
基金supported in part by the National Natural Science Foundation of China (Grant Nos.62273314,U21A20141,and 51821003)Fundamental Research Program of Shanxi Province (Grant No.202303021224008)Shanxi Province Key Laboratory of Quantum Sensing and Precision Measure-ment (Grant No.201905D121001).
文摘It is found that when the parity–time symmetry phenomenon is introduced into the resonant optical gyro system and it works near the exceptional point,the sensitivity can in theory be significantly amplified at low angular rate.However,in fact,the exceptional point is easily disturbed by external environmental variables,which means that it depends on harsh experimental environment and strong control ability,so it is difficult to move towards practical application.Here,we propose a new angular rate sensor structure based on exceptional surface,which has the advantages of high sensitivity and high robustness.The system consists of two fiber-optic ring resonators and two optical loop mirrors,and one of the resonators contains a variable ratio coupler and a variable optical attenuator.We theoretically analyze the system response,and the effects of phase and coupling ratio on the system response.Finally,compared with the conventional resonant gyro,the sensitivity of this exceptional surface angular rate sensor can be improved by about 300 times at low speed.In addition,by changing the loss coefficient in the ring resonator,we can achieve a wide range of 600 rad/s.This scheme provides a new approach for the development of ultra-high sensitivity and wide range angular rate sensors in the future.
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(Grant No.2022YFA1404402)the National Natural Science Foundation of China(Grant Nos.12174190,11634006,12074286,and 81127901)+1 种基金the High-Performance Computing Center of Collaborative Innovation Center of Advanced Microstructuresthe the Priority Academic Program Development of Jiangsu Higher Education Institutions。
文摘Transformation acoustics(TA)has emerged as a powerful tool for designing several intriguing conceptual devices,which can manipulate acoustic waves in a flexible manner,yet their applications are limited in Hermitian materials.In this work,we propose the theory of complex-coordinate transformation acoustics(CCTA)and verify the effectiveness in realizing acoustic non-Hermitian metamaterials.Especially,we apply this theory for the first time to the design of acoustic parity-time(PT)and antisymmetric parity-time(APT)metamaterials and demonstrate two distinctive examples.First,we use this method to obtain the exceptional points(EPs)of the PT/APT system and observe the spontaneous phase transition of the scattering matrix in the transformation parameter space.Second,by selecting the Jacobian matrix's constitutive parameters,the PT/APT-symmetric system can also be configured to approach the zero and pole of the scattering matrix,behaving as an acoustic coherent perfect absorber and equivalent laser.We envision our proposed CCTAbased paradigm to open the way for exploring the non-Hermitian physics and finding application in the design of acoustic functional devices such as absorbers and amplifiers whose material parameters are hard to realize by using the conventional transformation method.
基金supported by the National Research Foundation,Singapore and A*STAR under its CQT Bridging Grant,the Ministry of Education,Singapore(MOE award number:MOE-T2EP50222-0003)the Fundamental Research Funds for the Central Universities.
文摘Entanglement scaling behavior provides an established diag-nostic for critical phase transitions.Deeply rooted in boundary conformal field theory[1],it associates logarithmic entanglement entropy scalinglog L with 1D criticality[2,3].Recently,such scaling behavior has been challenged in non-Hermitian systems:at exceptional points(EPs)[4],geometric defectiveness and proba-bility non-conservation lead to anomalous negative entanglement entropy in free-fermion systems[5],corresponding to a negative central charge as described by nonunitary conformal field theory[6].Despite these complications,all known non-Hermitian free-fermion critical systems still exhibit the celebratedL scaling.
基金the National Natural Science Foundation of China(Grant Nos.11935006,11774086,and 12064010)Science and Technology Innovation Program of Hunan Province,China(Grant No.2020RC4047)+1 种基金Natural Science Foundation of Hunan Province of China(Grant No.2021JJ20036)Natural Science Foundation of Jiangxi Province of China(Grant No.20192ACB21002)。
文摘Non-Hermitian systems can exhibit unconventional spectral singularities called exceptional points(EPs).Various EP sensors have been fabricated in recent years,showing strong spectral responses to external signals.Here we propose how to achieve a nonlinear anti-parity-time(PT)gyroscope by spinning an optical resonator.We show that,in the absence of any nonlinearity,the sensitivity or optical mode splitting of the linear device can be magnified up to 3 orders compared to that of the conventional device without EPs.Remarkably,the PT symmetry can be broken when including the Kerr nonlinearity of the materials and,as a result,the detection threshold can be significantly lowered,i.e.,much weaker rotations which are well beyond the ability of a linear gyroscope can now be detected with the nonlinear device.Our work shows the powerful ability of PT gyroscopes in practice to achieve ultrasensitive rotation measurement.
基金supported by the National Natural Science Foundation of China(Grant Nos.12064045,11364044 and 11864043)the Science and Technology Development Foundation of Jilin Province(Grant No.20180101342JC)Science and Technology Research Project of Education Department of Jilin Province(Grant No.JJKH20200509KJ).
文摘We demonstrate the possibility of dual-band unidirectional reflectionlessness in a non-Hermitian quantum system composed of a plasmonic waveguide and two end-coupled plasmonic cavities(PCs).Our scheme exhibits dual-band unidirectional reflectionlessness can be obtained at exceptional points by properly adjusting the coupling strength between two PCs,the ratio of decay rates of two PCs,and the ratio of plasmonic cavity-waveguide coupling strengths.As a valuable feature,the quality factor reaches to~175.4 in forward direction,while the backward quality factor is close to~188.2.
