The tunneling conductance of two kinds of tunnel junctions with time-reversal symmetry breaking,normal metal/insulator/ferromagnetic metal/dx_(2-y2)+is-wave superconductor(NM/I/FM/dx_(2-y2)+is-wave SC)and NM/I/FM/dx_(...The tunneling conductance of two kinds of tunnel junctions with time-reversal symmetry breaking,normal metal/insulator/ferromagnetic metal/dx_(2-y2)+is-wave superconductor(NM/I/FM/dx_(2-y2)+is-wave SC)and NM/I/FM/dx_(2-y2)+idxy-wave SC,is calculated using the extended Blonder-Tinkham-Klapwijk theoretical method.The ratio of the subdominant s-wave and dxy-wave components to the dominant dx_(2-y2)-wave component is expressed byΔ_(s)/Δ_(D)andΔ_(d)/Δ_(D),respectively.Results show that for NM/I/FM/dx_(2-y2)+is-wave SC tunnel junctions,the splitting of the zero-bias conductance peak(ZBCP)is obtained and the splitting peaks appear at eV/Δ_(0)=±Δ_(s)/Δ_(D)with eV the applied bias voltage andΔ_(0)the zero temperature energy gap of SC.For NM/I/FM/dx_(2-y2)+idxy-wave SC tunnel junctions,there are also conductance peaks at eV/Δ_(0)=±Δ_(d)/Δ_(D)but the ZBCP does not split.For the two types of tunnel junctions,the completely reversed tunnel conductance spectrum indicates that when the exchange energy in FM is increased to a certain value,the proximity effect transforms the tunnel junctions from the'0 state'to the'πstate'.The shortening of the transport quasiparticle lifetime can weaken the proximity effect to smooth out the dips and peaks in the tunnel spectrum.This is considered a possible reason that the ZBCP splitting was not observed in some previous experiments.It is expected that these analysis results can serve as a guide for future experiments and the relevant conclusions can be confirmed.展开更多
Atomic nonlinear interferometry has wide applications in quantum metrology and quantum information science.Here we propose a nonlinear time-reversal interferometry scheme with high robustness and metrological gain bas...Atomic nonlinear interferometry has wide applications in quantum metrology and quantum information science.Here we propose a nonlinear time-reversal interferometry scheme with high robustness and metrological gain based on the spin squeezing generated by arbitrary quadratic collective-spin interaction,which could be described by the Lipkin–Meshkov–Glick(LMG)model.We optimize the squeezing process,encoding process,and anti-squeezing process,finding that the two particular cases of the LMG model,one-axis twisting and two-axis twisting outperform in robustness and precision,respectively.Moreover,we propose a Floquet driving method to realize equivalent time reverse in the atomic system,which leads to high performance in precision,robustness,and operability.Our study sets a benchmark for achieving high precision and high robustness in atomic nonlinear interferometry.展开更多
A novel method combining the time-reversal method(TRM)with wavelet analysis was proposed for damage imaging in mesoscale concrete modeling.The damage was imaged by the convergence of time-reversed wave signals after w...A novel method combining the time-reversal method(TRM)with wavelet analysis was proposed for damage imaging in mesoscale concrete modeling.The damage was imaged by the convergence of time-reversed wave signals after wavelet analysis.Through numerical study,three concrete models of different damage sizes were built with randomly distributed aggregate particles.The time-reversal process was simulated using the reverse damage-scattered ultrasonic wave signals as excitations recorded by the sensors.Then,the wavelet analysis was employed to extract certain frequency component,which can enhance detection precision and the signalto-noise ratio.The damage imaging showed clearly the location of the defect.The results from experimental testing also demonstrated that this detection technique is an efficient and effective method for damage imaging in mesoscale concrete.展开更多
As an example of our new approach to complex near-field （NF） scattering of electromagnetic waves, the timereversal （TR） transmission process on an NF current-element array is mapped to the statistical process on a...As an example of our new approach to complex near-field （NF） scattering of electromagnetic waves, the timereversal （TR） transmission process on an NF current-element array is mapped to the statistical process on a kinetic Ising transmission chain. Equilibrium statistical mechanics and non-equilibrium Monte Carlo （MC） dynamics help us to find signal jamming, aging, annihilating, creating, and TR symmetry breaking on the chain with inevitable background noises; and these results are general in NF systems where complex electromagnetic scattering arises.展开更多
The electromagnetic time-reversal(TR)technique has the characteristics of spatiotemporal focusing in a time-reversal cavity(TRC),which can be used for pulse compression,thus forming an electromagnetic pulse with high ...The electromagnetic time-reversal(TR)technique has the characteristics of spatiotemporal focusing in a time-reversal cavity(TRC),which can be used for pulse compression,thus forming an electromagnetic pulse with high peak power.A time-reversed pulse-compression method in a single channel has high pulse compression gain.However,single channel pulse compression can only generate limited gain.This paper proposes a novel TR power-combination method in a multichannel TRC to obtain higher peak power based on TR pulse-compression theory.First,the TR power-combination model is given,and the crosstalk properties of the associated channel and the influence of the reversal performance are studied.Then,the power-combination performances for the TR pulse compression,such as combined signal to noise ratio(SNR)and combined compression gain,are analyzed by numerical simulation and experimental methods.The results show that the proposed method has obvious advantages over pulse-compression methods using a single channel cavity,and is more convenient for power combination.展开更多
The performance of time-reversal focusing with a horizontal line array at different depths is investigated by normal mode modeling and computer simulation. It is observed that the focusing performance of a bottom-moun...The performance of time-reversal focusing with a horizontal line array at different depths is investigated by normal mode modeling and computer simulation. It is observed that the focusing performance of a bottom-mounted horizontal time-reversal array is much better than that of a horizontal time-reversal array at other depths in shallow water. The normal mode modeling is used to explain this result. The absolute values of the modes at different depths are compared. It is shown that the number of modes whose absolute values close to zero is smaller at the bottom than that at other depths. It means that the horizontal time-reversal array deployed at the bottom can sample more modes, obtain more information of the probe source and achieve better focusing performance. The numerical simulations of time-reversal focusing performance under various conditions, such as different sound speed profiles, and different bottom parameters, lead to similar results.展开更多
A formalism is developed for calculating the signal of the violation of time-reversal invariance,provided that space-reflection(parity)invariance is conserved during the scattering of tensor-polarized deuterons on vec...A formalism is developed for calculating the signal of the violation of time-reversal invariance,provided that space-reflection(parity)invariance is conserved during the scattering of tensor-polarized deuterons on vector-polarized deuterons.The formalism is based on Glauber theory and fully considers the spin dependence of NN elastic scattering amplitudes and the spin structure of colliding deuterons.Numerical calculations are performed in the laboratory proton energy range T_(p)=0.1–1.2 GeV using the SAID database for spin amplitudes and in the energy region of the SPD NICA experiment corresponding to the invariant mass of the interacting nucleon pairs√S_(NN)=2.5-25GeV–25 GeV,using two phenomenological models of PN elastic scattering.It is found that only one type of the time-reversal non-invariant parity conserving interaction gives a non-zero contribution to the signal in question,which is important for isolating an unknown constant of this interaction from the corresponding data.展开更多
Spontaneous time-reversal symmetry breaking plays an important role in studying strongly correlated unconventional superconductors.When two superconducting gap functions with different symmetries compete,the relative ...Spontaneous time-reversal symmetry breaking plays an important role in studying strongly correlated unconventional superconductors.When two superconducting gap functions with different symmetries compete,the relative phase channel(θ_(-)≡θ_(1)-θ_(2))exhibits an Ising-type Z_(2) symmetry due to the second order Josephson coupling,where θ_(1,2) are the phases of two gap functions.In contrast,the U(1) symmetry in the channel of θ_(+)≡(θ_(1)+θ_(2))/2 is intact.The phase locking,i.e.,ordering of θ_(-),can take place in the phase fluctuation regime before the onset of superconductivity,i.e.,when θ_(+) is disordered.If θ_(-) is pinned at ±π/2,then timereversal symmetry is broken in the normal state,otherwise,if θ_(-)=0,or,π,rotational symmetry is broken,leading to a nematic normal state.In both cases,the order parameters possess a 4-fermion structure beyond the scope of mean-field theory,which can be viewed as a high order symmetry breaking.We employ an effective two-component XY-model assisted by a renormalization group analysis to address this problem.As a natural by-product,we also find the other interesting intermediate phase corresponds to ordering of θ_+ but with θ_(-)disordered.This is the quartetting,or,charge-4e,superconductivity,which occurs above the low temperature Z_(2)-breaking charge-2e superconducting phase.Our results provide useful guidance for studying novel symmetry breaking phases in strongly correlated superconductors.展开更多
It is well known that in one-dimensional(1D) crystalline insulators,the electric polarization is a manifestation of Berry phase,which can not be quantized by time-reversal symmetry(TRS) as in Hermitian physics TRS doe...It is well known that in one-dimensional(1D) crystalline insulators,the electric polarization is a manifestation of Berry phase,which can not be quantized by time-reversal symmetry(TRS) as in Hermitian physics TRS does not induce any topological phase in one dimension.In this paper we report that even though associated with complex eigenenergies a 1D non-Hermitian insulator obeying only TRS is capable of presenting quantized bulk polarization.The underlying physical reason is unveiled:TRS guarantees the complex energies to come in pair(E,E*),and the corresponding decaying and amplifying wave functions also come in pair and have the same variation rate,hence,giving rise to a stable wannier center.The electron transport is performed by means of charge pumping process,which verifies the physical mechanism above.At last,we discuss the possible experimental implementation of the proposed model by means of twisted-π gauge flux.展开更多
A study on the self-adaptive focusing of acoustical beam in the solid by Time Reversal (TR) method is presented. The theoretical analyses and experiments show that TR can compensate the path difference of sound pulse ...A study on the self-adaptive focusing of acoustical beam in the solid by Time Reversal (TR) method is presented. The theoretical analyses and experiments show that TR can compensate the path difference of sound pulse in solid, and generate the self-focusing of longitudinal and shear waves at the same time. The experimental values of the focusing processing gain agree with the theoretical values.展开更多
The continuous-time quantum walk is a basic model for studying quantum transport and developing quantum-enhanced algorithms. Recent studies show that by introducing a phase into the standard continuous-time quantum wa...The continuous-time quantum walk is a basic model for studying quantum transport and developing quantum-enhanced algorithms. Recent studies show that by introducing a phase into the standard continuous-time quantum walk model, the time-reversal symmetry can be broken without changing the Hermitian property of the Hamiltonian. The time-reversal symmetry breaking quantum walk shows advantages in quantum transport, such as perfect state transfer, directional control, transport speedup, and quantum transport efficiency enhancement. In this work, we implement the time-reversal symmetry breaking quantum walks on a reconfigurable silicon photonic chip and demonstrate the enhancement introduced by breaking time-reversal symmetry. Perfect state transfer on a three-site ring, a quantum switch implemented on a six-site graph, and transport speedup using a linear chain of triangles are demonstrated with high fidelity. Time-reversal asymmetry has also been used in a simplified light-harvesting model,implying the potential of time-reversal symmetry breaking in photosynthesis investigations.展开更多
In this paper, a frequency domain decision feedback equalizer is proposed for single carrier transmission with time-reversal space-time block coding （TR-STBC）. It is shown that the diagonal decision feedback equaliz...In this paper, a frequency domain decision feedback equalizer is proposed for single carrier transmission with time-reversal space-time block coding （TR-STBC）. It is shown that the diagonal decision feedback equalizer matrix can be calculated from the frequency domain channel response. Under the perfect feedback assumption, the proposed equalizer can approach matched filter bound （MFB）. Compared with the existing time domain decision feedback equalizer, the proposed equalizer exhibits better performance with the same equalization complexity.展开更多
Time reversal is a key component of time-reverse migration and source location using wavefield extrapolation.The implementation of time reversal depends on the time symmetry of wave equations in acoustic and elastic m...Time reversal is a key component of time-reverse migration and source location using wavefield extrapolation.The implementation of time reversal depends on the time symmetry of wave equations in acoustic and elastic media.This symmetry in time is no longer valid in attenuative medium.Not only the velocity is anisotropic in shale oil and gas reservoirs,but also the attenuation is usually anisotropic,which can be characterized by viscoelastic orthotropic media.In this paper,the fractional order viscoelastic anisotropic wave equation is used to decouple the energy dissipation and the velocity dispersion.By changing the sign of the dissipation term during backpropagation,the anisotropic attenuation is compensated and the time symmetry is restored.The attenuation compensation time-reverse location algorithm can eff ectively locate the source in viscoelastic orthotropic media.Compared to cases without attenuation compensation or using isotropic attenuation compensation,this method can remove location error caused by anisotropic attenuation and improve the imaging eff ect of the source.This paper verifi es the eff ectiveness of the method through theoretical analysis and model testing.展开更多
Focusing light though scattering media beyond the ballistic regime is a challenging task in biomedical optical imaging.This challenge can be overcome by wavefront shaping technique,in which a time reversed(TR)wavefron...Focusing light though scattering media beyond the ballistic regime is a challenging task in biomedical optical imaging.This challenge can be overcome by wavefront shaping technique,in which a time reversed(TR)wavefront of scattered light is generated to suppress the scattering.In previous TR optical focusing experiments,a phase only spatial light modulator(SLM)has.been typically used to control the wavefront of incident light.Unfortunately,although the phase information is reconstructed by the phase-only SLM,the amplitude information is lost,resulting in decreased peak to-background ratio(PBR)of optical focusing in the TR wavefront recon-struction.A new method of TR optical focusing through scattering media is proposed here,which numerically reonstructs the full phase and amplitude of a simulated scattered light field by using a single phase only SLM.Simulation results and the proposed optical setup show that the time-reversal of a fully developed speckle field can be digially implemented with both phase and ampltude recovery,affording a way to improve the performance of light focusing through scattering media.展开更多
Boundary effect and time-reversal symmetry are hot topics in active matter. We present a biology-inspired robotenvironment-interaction active matter system with the field-drive motion and the rules of resource search,...Boundary effect and time-reversal symmetry are hot topics in active matter. We present a biology-inspired robotenvironment-interaction active matter system with the field-drive motion and the rules of resource search, resource consumption, and resource recovery. In an environmental compression–expansion cycle, the swarm emerges a series of boundary-dependent phase transitions, and the whole evolution process is time-reversal symmetry-breaking;we call this phenomenon “orderly hysteresis”. We present the influence of the environmental recovery rate on the dynamic collective behavior of the swarm.展开更多
In this paper, split-ring-based metamaterial sheets are designed for the purpose of achieving far-field subwavelength focusing, with the aid of a time-reversal technique. The metamaterial sheets are inserted into a su...In this paper, split-ring-based metamaterial sheets are designed for the purpose of achieving far-field subwavelength focusing, with the aid of a time-reversal technique. The metamaterial sheets are inserted into a subwavelength array consist- ing of four element antennas, with the element spacing being as small as 1/15 of a wavelength. Experiments are performed to investigate the effect of the metamaterial sheets on the focusing resolution. The results demonstrate that in the presence of the metamaterial sheets, the subwavelength array exhibits the ability to achieve super-resolution focusing, while there is no super-resolution focusing without the metamaterial sheets. Further investigation shows that the metamaterial sheets are contributive to achieving super-resolution by weakening the cross-correlations of the channel impulse responses between the array elements.展开更多
An efficient hybrid time reversal（TR） imaging method based on signal subspace and noise subspace is proposed for electromagnetic superresolution detecting and imaging. First, the locations of targets are estimated b...An efficient hybrid time reversal（TR） imaging method based on signal subspace and noise subspace is proposed for electromagnetic superresolution detecting and imaging. First, the locations of targets are estimated by the transmitting-mode decomposition of the TR operator（DORT） method employing the signal subspace. Then, the TR multiple signal classification（TR-MUSIC）method employing the noise subspace is used in the estimated target area to get the superresolution imaging of targets. Two examples with homogeneous and inhomogeneous background mediums are considered, respectively. The results show that the proposed hybrid method has advantages in CPU time and memory cost because of the combination of rough and fine imaging.展开更多
Microseismic source location is the essential factor in microseismic monitoring technology, and its loca- tion precision has a large impact on the performance of the technique. Here, we discuss the problem of low-prec...Microseismic source location is the essential factor in microseismic monitoring technology, and its loca- tion precision has a large impact on the performance of the technique. Here, we discuss the problem of low-precision location identification for microseismic events in a mine, as may be obtained using conven-tional location methods that are based on arrival time. In this paper, microseismic location characteristics in mining are analyzed according to the characteristics of the mine＇s microseismic wavefield. We review research progress in mine-related microseismic source location methods in recent years, including the combination of the Geiger method with the linear method, combined microseismic event location method, optimization of relative location method, location method without pre-measured velocity, and location method without arrival time picking. The advantages and disadvantages of these methods are discussed, along with their feasible conditions. The influences of geophone distribution, first arrival time picking, and the velocity model on microseismic source location are analyzed, and measures are proposed to influence these factors. Approaches to solve the problem under study include adopting information fusion, combining and optimizing existing methods, and creating new methods to realize high-precision microseismic source location. Optimization of the velocity structure, along with applications of the time-reversal imaging technique, passive time-reversal mirror, and relative interferometric imag-ing, are expected to greatly improve microseismic location precision in mines. This paper also discusses the potential application of information fusion and deep learning methods in microseismic source location in mines. These new and innovative location methods for microseismic source location have extensive prospects for development.展开更多
We prepare a class of locally resonant （LR） sonic materials. The experiments demonstrate that the resonant frequency decreases with the increasing density of the scattering unit cores or with the reducing elastic co...We prepare a class of locally resonant （LR） sonic materials. The experiments demonstrate that the resonant frequency decreases with the increasing density of the scattering unit cores or with the reducing elastic constants of the silicone rubber coating. By combining three LR layers of different resonant frequencies and choosing 10 dB as the threshold of relative attenuation, we obtain an ultrawide bandgap （200-950Hz） sound material with an average transmission loss 22 dB lower than that dictated by mass density law.展开更多
基金supported by the Fundamental Research Funds for the Central Universities(Grant Nos.23CX03016A and 24CX030009A)。
文摘The tunneling conductance of two kinds of tunnel junctions with time-reversal symmetry breaking,normal metal/insulator/ferromagnetic metal/dx_(2-y2)+is-wave superconductor(NM/I/FM/dx_(2-y2)+is-wave SC)and NM/I/FM/dx_(2-y2)+idxy-wave SC,is calculated using the extended Blonder-Tinkham-Klapwijk theoretical method.The ratio of the subdominant s-wave and dxy-wave components to the dominant dx_(2-y2)-wave component is expressed byΔ_(s)/Δ_(D)andΔ_(d)/Δ_(D),respectively.Results show that for NM/I/FM/dx_(2-y2)+is-wave SC tunnel junctions,the splitting of the zero-bias conductance peak(ZBCP)is obtained and the splitting peaks appear at eV/Δ_(0)=±Δ_(s)/Δ_(D)with eV the applied bias voltage andΔ_(0)the zero temperature energy gap of SC.For NM/I/FM/dx_(2-y2)+idxy-wave SC tunnel junctions,there are also conductance peaks at eV/Δ_(0)=±Δ_(d)/Δ_(D)but the ZBCP does not split.For the two types of tunnel junctions,the completely reversed tunnel conductance spectrum indicates that when the exchange energy in FM is increased to a certain value,the proximity effect transforms the tunnel junctions from the'0 state'to the'πstate'.The shortening of the transport quasiparticle lifetime can weaken the proximity effect to smooth out the dips and peaks in the tunnel spectrum.This is considered a possible reason that the ZBCP splitting was not observed in some previous experiments.It is expected that these analysis results can serve as a guide for future experiments and the relevant conclusions can be confirmed.
基金Project supported by the National Key R&D Program of China (Grant No.2023YFA1407600)the National Natural Science Foundation of China (Grant Nos.12275145,92050110,91736106,11674390,and 91836302)。
文摘Atomic nonlinear interferometry has wide applications in quantum metrology and quantum information science.Here we propose a nonlinear time-reversal interferometry scheme with high robustness and metrological gain based on the spin squeezing generated by arbitrary quadratic collective-spin interaction,which could be described by the Lipkin–Meshkov–Glick(LMG)model.We optimize the squeezing process,encoding process,and anti-squeezing process,finding that the two particular cases of the LMG model,one-axis twisting and two-axis twisting outperform in robustness and precision,respectively.Moreover,we propose a Floquet driving method to realize equivalent time reverse in the atomic system,which leads to high performance in precision,robustness,and operability.Our study sets a benchmark for achieving high precision and high robustness in atomic nonlinear interferometry.
基金The work described in this article was supported by the National Natural Science Foundation of China(Grant Nos.11520101001 and 11702118)the Natural Science Foundation of Jiangsu Province(Grant No.17KJB130005)the Basic Research Program of Jiangsu Education Department(Grant No.BK20170520),all of which are gratefully acknowledged.
文摘A novel method combining the time-reversal method(TRM)with wavelet analysis was proposed for damage imaging in mesoscale concrete modeling.The damage was imaged by the convergence of time-reversed wave signals after wavelet analysis.Through numerical study,three concrete models of different damage sizes were built with randomly distributed aggregate particles.The time-reversal process was simulated using the reverse damage-scattered ultrasonic wave signals as excitations recorded by the sensors.Then,the wavelet analysis was employed to extract certain frequency component,which can enhance detection precision and the signalto-noise ratio.The damage imaging showed clearly the location of the defect.The results from experimental testing also demonstrated that this detection technique is an efficient and effective method for damage imaging in mesoscale concrete.
基金supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No.20100185110021)the National Natural Science Foundation of China (Grant No.61071031)
文摘As an example of our new approach to complex near-field （NF） scattering of electromagnetic waves, the timereversal （TR） transmission process on an NF current-element array is mapped to the statistical process on a kinetic Ising transmission chain. Equilibrium statistical mechanics and non-equilibrium Monte Carlo （MC） dynamics help us to find signal jamming, aging, annihilating, creating, and TR symmetry breaking on the chain with inevitable background noises; and these results are general in NF systems where complex electromagnetic scattering arises.
基金Project supported by the National Key R&D Program of China(Grant No.2021YFC2203503)。
文摘The electromagnetic time-reversal(TR)technique has the characteristics of spatiotemporal focusing in a time-reversal cavity(TRC),which can be used for pulse compression,thus forming an electromagnetic pulse with high peak power.A time-reversed pulse-compression method in a single channel has high pulse compression gain.However,single channel pulse compression can only generate limited gain.This paper proposes a novel TR power-combination method in a multichannel TRC to obtain higher peak power based on TR pulse-compression theory.First,the TR power-combination model is given,and the crosstalk properties of the associated channel and the influence of the reversal performance are studied.Then,the power-combination performances for the TR pulse compression,such as combined signal to noise ratio(SNR)and combined compression gain,are analyzed by numerical simulation and experimental methods.The results show that the proposed method has obvious advantages over pulse-compression methods using a single channel cavity,and is more convenient for power combination.
基金Project supported by the National Natural Science Foundation of China (Grant No. 10774119)the Program for New Century Excellent Talents in University (Grant No. NCET-08-0455)+2 种基金the Natural Science Foundation of Shaanxi Province of China(Grant No. SJ08F07)the Foundation of National Laboratory of Acousticsthe Northwestern Polytechnical University (NPU) Foundation for Fundamental Research
文摘The performance of time-reversal focusing with a horizontal line array at different depths is investigated by normal mode modeling and computer simulation. It is observed that the focusing performance of a bottom-mounted horizontal time-reversal array is much better than that of a horizontal time-reversal array at other depths in shallow water. The normal mode modeling is used to explain this result. The absolute values of the modes at different depths are compared. It is shown that the number of modes whose absolute values close to zero is smaller at the bottom than that at other depths. It means that the horizontal time-reversal array deployed at the bottom can sample more modes, obtain more information of the probe source and achieve better focusing performance. The numerical simulations of time-reversal focusing performance under various conditions, such as different sound speed profiles, and different bottom parameters, lead to similar results.
基金the expense of the grant from the Russian Science Foundation(23-22-00123,https://rscf.ru/en/project/23-22-00123/)。
文摘A formalism is developed for calculating the signal of the violation of time-reversal invariance,provided that space-reflection(parity)invariance is conserved during the scattering of tensor-polarized deuterons on vector-polarized deuterons.The formalism is based on Glauber theory and fully considers the spin dependence of NN elastic scattering amplitudes and the spin structure of colliding deuterons.Numerical calculations are performed in the laboratory proton energy range T_(p)=0.1–1.2 GeV using the SAID database for spin amplitudes and in the energy region of the SPD NICA experiment corresponding to the invariant mass of the interacting nucleon pairs√S_(NN)=2.5-25GeV–25 GeV,using two phenomenological models of PN elastic scattering.It is found that only one type of the time-reversal non-invariant parity conserving interaction gives a non-zero contribution to the signal in question,which is important for isolating an unknown constant of this interaction from the corresponding data.
基金supported by a startup funding of UCSD and the National Science Foundation (Grant No. DMR-2238360)supported by the National Natural Science Foundation of China (Grant Nos. 12234016, and 12174317)supported by the New Cornerstone Science Foundation。
文摘Spontaneous time-reversal symmetry breaking plays an important role in studying strongly correlated unconventional superconductors.When two superconducting gap functions with different symmetries compete,the relative phase channel(θ_(-)≡θ_(1)-θ_(2))exhibits an Ising-type Z_(2) symmetry due to the second order Josephson coupling,where θ_(1,2) are the phases of two gap functions.In contrast,the U(1) symmetry in the channel of θ_(+)≡(θ_(1)+θ_(2))/2 is intact.The phase locking,i.e.,ordering of θ_(-),can take place in the phase fluctuation regime before the onset of superconductivity,i.e.,when θ_(+) is disordered.If θ_(-) is pinned at ±π/2,then timereversal symmetry is broken in the normal state,otherwise,if θ_(-)=0,or,π,rotational symmetry is broken,leading to a nematic normal state.In both cases,the order parameters possess a 4-fermion structure beyond the scope of mean-field theory,which can be viewed as a high order symmetry breaking.We employ an effective two-component XY-model assisted by a renormalization group analysis to address this problem.As a natural by-product,we also find the other interesting intermediate phase corresponds to ordering of θ_+ but with θ_(-)disordered.This is the quartetting,or,charge-4e,superconductivity,which occurs above the low temperature Z_(2)-breaking charge-2e superconducting phase.Our results provide useful guidance for studying novel symmetry breaking phases in strongly correlated superconductors.
基金supported by the National Natural Science Foundation of China (Grant Nos.61805141,and 62305113)。
文摘It is well known that in one-dimensional(1D) crystalline insulators,the electric polarization is a manifestation of Berry phase,which can not be quantized by time-reversal symmetry(TRS) as in Hermitian physics TRS does not induce any topological phase in one dimension.In this paper we report that even though associated with complex eigenenergies a 1D non-Hermitian insulator obeying only TRS is capable of presenting quantized bulk polarization.The underlying physical reason is unveiled:TRS guarantees the complex energies to come in pair(E,E*),and the corresponding decaying and amplifying wave functions also come in pair and have the same variation rate,hence,giving rise to a stable wannier center.The electron transport is performed by means of charge pumping process,which verifies the physical mechanism above.At last,we discuss the possible experimental implementation of the proposed model by means of twisted-π gauge flux.
基金This project is supported by National Natural Science Foundation of China and the President Foundationof Institute of Acoustic
文摘A study on the self-adaptive focusing of acoustical beam in the solid by Time Reversal (TR) method is presented. The theoretical analyses and experiments show that TR can compensate the path difference of sound pulse in solid, and generate the self-focusing of longitudinal and shear waves at the same time. The experimental values of the focusing processing gain agree with the theoretical values.
基金supported by the National Key Research and Development Program of China (Grant Nos. 2019YFA0308700, and 2017YFA0303700)。
文摘The continuous-time quantum walk is a basic model for studying quantum transport and developing quantum-enhanced algorithms. Recent studies show that by introducing a phase into the standard continuous-time quantum walk model, the time-reversal symmetry can be broken without changing the Hermitian property of the Hamiltonian. The time-reversal symmetry breaking quantum walk shows advantages in quantum transport, such as perfect state transfer, directional control, transport speedup, and quantum transport efficiency enhancement. In this work, we implement the time-reversal symmetry breaking quantum walks on a reconfigurable silicon photonic chip and demonstrate the enhancement introduced by breaking time-reversal symmetry. Perfect state transfer on a three-site ring, a quantum switch implemented on a six-site graph, and transport speedup using a linear chain of triangles are demonstrated with high fidelity. Time-reversal asymmetry has also been used in a simplified light-harvesting model,implying the potential of time-reversal symmetry breaking in photosynthesis investigations.
基金supported by the National Basic Research Program of China (2009CB320401)the National Key Scientific and Technological Project of China (2010ZX03003-001,2010ZX03003-003-01)+2 种基金the Research Funds for Doctoral Program of Higher Education of China (20090005110003)the National Natural Science Foundation of China (60902048)the Fundamental Research Funds for the Central Universities (2010PTB-03-04 G470220)
文摘In this paper, a frequency domain decision feedback equalizer is proposed for single carrier transmission with time-reversal space-time block coding （TR-STBC）. It is shown that the diagonal decision feedback equalizer matrix can be calculated from the frequency domain channel response. Under the perfect feedback assumption, the proposed equalizer can approach matched filter bound （MFB）. Compared with the existing time domain decision feedback equalizer, the proposed equalizer exhibits better performance with the same equalization complexity.
基金This work was supported by National Natural Science Foundation of China(No.41504097,41874153).
文摘Time reversal is a key component of time-reverse migration and source location using wavefield extrapolation.The implementation of time reversal depends on the time symmetry of wave equations in acoustic and elastic media.This symmetry in time is no longer valid in attenuative medium.Not only the velocity is anisotropic in shale oil and gas reservoirs,but also the attenuation is usually anisotropic,which can be characterized by viscoelastic orthotropic media.In this paper,the fractional order viscoelastic anisotropic wave equation is used to decouple the energy dissipation and the velocity dispersion.By changing the sign of the dissipation term during backpropagation,the anisotropic attenuation is compensated and the time symmetry is restored.The attenuation compensation time-reverse location algorithm can eff ectively locate the source in viscoelastic orthotropic media.Compared to cases without attenuation compensation or using isotropic attenuation compensation,this method can remove location error caused by anisotropic attenuation and improve the imaging eff ect of the source.This paper verifi es the eff ectiveness of the method through theoretical analysis and model testing.
基金supported by the National Science Foundation of China (61177018)the Program for New Century Excellent Talents in University (NECT-11-0596)Beijing Nova Program (2011066).
文摘Focusing light though scattering media beyond the ballistic regime is a challenging task in biomedical optical imaging.This challenge can be overcome by wavefront shaping technique,in which a time reversed(TR)wavefront of scattered light is generated to suppress the scattering.In previous TR optical focusing experiments,a phase only spatial light modulator(SLM)has.been typically used to control the wavefront of incident light.Unfortunately,although the phase information is reconstructed by the phase-only SLM,the amplitude information is lost,resulting in decreased peak to-background ratio(PBR)of optical focusing in the TR wavefront recon-struction.A new method of TR optical focusing through scattering media is proposed here,which numerically reonstructs the full phase and amplitude of a simulated scattered light field by using a single phase only SLM.Simulation results and the proposed optical setup show that the time-reversal of a fully developed speckle field can be digially implemented with both phase and ampltude recovery,affording a way to improve the performance of light focusing through scattering media.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 11974066 and 12174041)the Seed Grants from the Wenzhou Institute, University of Chinese Academy of Sciences (Grant No. WIUCASQD2021002)。
文摘Boundary effect and time-reversal symmetry are hot topics in active matter. We present a biology-inspired robotenvironment-interaction active matter system with the field-drive motion and the rules of resource search, resource consumption, and resource recovery. In an environmental compression–expansion cycle, the swarm emerges a series of boundary-dependent phase transitions, and the whole evolution process is time-reversal symmetry-breaking;we call this phenomenon “orderly hysteresis”. We present the influence of the environmental recovery rate on the dynamic collective behavior of the swarm.
基金supported by the National Natural Science Foundation of China(Grant Nos.61071031,61331007,and 61107018)the Research Fund for the Doctoral Program of Higher Education of China(Grant Nos.20100185110021 and 20120185130001)+1 种基金the Fundamental Research Funds for the Central Universities,China(Grant No.E02205205)the Project ITR1113,China
文摘In this paper, split-ring-based metamaterial sheets are designed for the purpose of achieving far-field subwavelength focusing, with the aid of a time-reversal technique. The metamaterial sheets are inserted into a subwavelength array consist- ing of four element antennas, with the element spacing being as small as 1/15 of a wavelength. Experiments are performed to investigate the effect of the metamaterial sheets on the focusing resolution. The results demonstrate that in the presence of the metamaterial sheets, the subwavelength array exhibits the ability to achieve super-resolution focusing, while there is no super-resolution focusing without the metamaterial sheets. Further investigation shows that the metamaterial sheets are contributive to achieving super-resolution by weakening the cross-correlations of the channel impulse responses between the array elements.
基金supported by the National Natural Science Foundation of China(6130127161331007)+2 种基金the Specialized Research Fund for the Doctoral Program of Higher Education of China(2011018512000820120185130001)the Fundamental Research Funds for Central Universities(ZYGX2012J043)
文摘An efficient hybrid time reversal（TR） imaging method based on signal subspace and noise subspace is proposed for electromagnetic superresolution detecting and imaging. First, the locations of targets are estimated by the transmitting-mode decomposition of the TR operator（DORT） method employing the signal subspace. Then, the TR multiple signal classification（TR-MUSIC）method employing the noise subspace is used in the estimated target area to get the superresolution imaging of targets. Two examples with homogeneous and inhomogeneous background mediums are considered, respectively. The results show that the proposed hybrid method has advantages in CPU time and memory cost because of the combination of rough and fine imaging.
基金This research was supported by the National Key Research and Development Program of China （2016YFC0801405 and 2017YFC0804105）, and the National Natural Science Foundation of China （51574250）. The authors also greatly indebted to Dr. Ye Chen, who is now working at the Research Centre of Photonics and Instrumentation at City, University of London, for his rigorous suggestions for this paper.
文摘Microseismic source location is the essential factor in microseismic monitoring technology, and its loca- tion precision has a large impact on the performance of the technique. Here, we discuss the problem of low-precision location identification for microseismic events in a mine, as may be obtained using conven-tional location methods that are based on arrival time. In this paper, microseismic location characteristics in mining are analyzed according to the characteristics of the mine＇s microseismic wavefield. We review research progress in mine-related microseismic source location methods in recent years, including the combination of the Geiger method with the linear method, combined microseismic event location method, optimization of relative location method, location method without pre-measured velocity, and location method without arrival time picking. The advantages and disadvantages of these methods are discussed, along with their feasible conditions. The influences of geophone distribution, first arrival time picking, and the velocity model on microseismic source location are analyzed, and measures are proposed to influence these factors. Approaches to solve the problem under study include adopting information fusion, combining and optimizing existing methods, and creating new methods to realize high-precision microseismic source location. Optimization of the velocity structure, along with applications of the time-reversal imaging technique, passive time-reversal mirror, and relative interferometric imag-ing, are expected to greatly improve microseismic location precision in mines. This paper also discusses the potential application of information fusion and deep learning methods in microseismic source location in mines. These new and innovative location methods for microseismic source location have extensive prospects for development.
文摘We prepare a class of locally resonant （LR） sonic materials. The experiments demonstrate that the resonant frequency decreases with the increasing density of the scattering unit cores or with the reducing elastic constants of the silicone rubber coating. By combining three LR layers of different resonant frequencies and choosing 10 dB as the threshold of relative attenuation, we obtain an ultrawide bandgap （200-950Hz） sound material with an average transmission loss 22 dB lower than that dictated by mass density law.
