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
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
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of time reversal depends on the time symmetry of wave equations in acoustic and elastic media.This symmetry in time is no longer valid in attenuative medium.Not only the velocity is anisotropic in shale oil and gas reservoirs,but also the attenuation is usually anisotropic,which can be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
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
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
文章先是阐述了能见度值在飞行指挥工作中的重要性,从能见度设备的测量原理上描述了飞虫类等对能见度测量值的影响。结合TR30LED大气透射仪的组成结构,深入分析飞虫、飞鸟活动如何导致其测量值异常变化,列举了对此类影响的各项常规防控...文章先是阐述了能见度值在飞行指挥工作中的重要性,从能见度设备的测量原理上描述了飞虫类等对能见度测量值的影响。结合TR30LED大气透射仪的组成结构,深入分析飞虫、飞鸟活动如何导致其测量值异常变化,列举了对此类影响的各项常规防控手段和措施,并通过设计开发技防措施和装置来进行防控,对TR30LED大气透射仪的飞虫飞鸟影响起到了积极的防护作用。This article first elaborates on the importance of visibility values in flight command work, and describes the impact of flying insects and other factors on visibility measurement values from the measurement principle of visibility equipment. Based on the composition and structure of the TR30LED atmospheric transmittance meter, this article deeply analyzes how the activities of flying insects and birds cause abnormal changes in their measurement values. Various conventional prevention and control measures for such effects are listed, and technical prevention measures and devices are designed and developed to prevent and control the impact of flying insects and birds on the TR30LED atmospheric transmittance meter, playing a positive protective role.展开更多
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.
文摘文章先是阐述了能见度值在飞行指挥工作中的重要性,从能见度设备的测量原理上描述了飞虫类等对能见度测量值的影响。结合TR30LED大气透射仪的组成结构,深入分析飞虫、飞鸟活动如何导致其测量值异常变化,列举了对此类影响的各项常规防控手段和措施,并通过设计开发技防措施和装置来进行防控,对TR30LED大气透射仪的飞虫飞鸟影响起到了积极的防护作用。This article first elaborates on the importance of visibility values in flight command work, and describes the impact of flying insects and other factors on visibility measurement values from the measurement principle of visibility equipment. Based on the composition and structure of the TR30LED atmospheric transmittance meter, this article deeply analyzes how the activities of flying insects and birds cause abnormal changes in their measurement values. Various conventional prevention and control measures for such effects are listed, and technical prevention measures and devices are designed and developed to prevent and control the impact of flying insects and birds on the TR30LED atmospheric transmittance meter, playing a positive protective role.
