bluuebunny/crossref_metadata_2025 huggingface dataset:
Two-dimensional distribution design of micro-prism for partial integrated light guide plate
Authors: Xu Ping , Yang Wei , Zhang Xu-Lin , Luo Tong-Zheng , Huang Yan-Yan ,   Institute of Micro-Nano Optoelectronic Technology, College of Electronic Science and Technology, Shenzhen University, Shenzhen 518060, China
Published: December 2020

The microstructure distribution on the bottom surface of the partial integrated light guide plate (PILGP) is the key to affecting the uniformity of the output light from the backlight module (BLM), which is one of the important factors in the BLM design. Based on the development trend of the BLM in light-weight and integration, many research institutes have realized the requirement for high luminance and luminance uniformity in the BLM by setting micro-prism structure on the surface of the light guide plate (LGP). In most of these studies, the length of the micro-prism structure is the same as the width of the LGP, and the optimization of the micro-prism distribution is performed only in the length direction of the LGP, which is a one-dimensional distribution. So, the long strip micro-prism structure cannot modulate the light in the axial direction, resulting in large area identity in the width direction of the LGP, thereby the luminance uniformity of the BLM is affected. In this paper, a design idea of two-dimensional distribution of the micro-prism on the bottom surface of the PILGP, which improves the luminance uniformity of the BLM, is proposed to solve the problem that the luminance uniformity is affected by large area identity caused by one-dimensional distribution design of the micro-prism. The small length micro-prism structure is used to break the limit of the axial distribution of the long strip micro-prism structure, and it can modulate the light in the axial direction. The Lighttools software is used to optimize the two-dimensional distribution of the micro-prism on the bottom surface of a 5.0-inch PILGP. Comparing with the PILGP with one-dimensional distribution of the micro-prism on the bottom surface, the simulation results show that the utilization of light energy, illuminance uniformity and luminance uniformity in the BLM with optimized two-dimensional distribution of the micro-prism on the bottom surface of the PILGP respectively reach 92.03%, 87.07% and 91.94%, which meet industry standards. And the illuminance uniformity increases by 10%. Meanwhile, the luminance diagram shows that the overall luminance uniformity of the BLM is improved effectively. Moreover, the distribution principle of the micro-prism on the bottom surface of the PILGP is analyzed and the physical mechanism is reasonably explained . The simulation results above show that the design concept of the two-dimensional distribution of micro-prism is feasible. The study results have a certain referential value for the development of the BLM in light-weight and integration.
Novel design of microstrip antenna array with low scattering performance
Authors: Lan Jun-Xiang , Cao Xiang-Yu , Gao Jun , Han Jiang-Feng , Liu Tao , Cong Li-Li , Wang Si-Ming ,   Information and Navigation College, Air Force Engineering University, Xi'an 710077, China
Published: December 2020

In this paper, the idea of electromagnetic surface (EMS) is introduced into the design of microstrip antenna array. The antenna element proposed in this paper is treated as an EMS element, whose reflection characteristics are taken into consideration in the process of antenna array design. Firstly, a rectangular patch antenna element is designed. Then, by cutting arc-shaped structure into a rectangular patch, another element is created to generate 180° ± 30° effective phase difference compared with original antenna element. As a consequence, 180° ± 30° effective phase difference is obtained from 5.5 GHz to 6.9 GHz for the y-polarized incidence. Meanwhile, for the x-polarized incidence, each of the two elements possesses high absorptivity over the operating frequency as a result of matching load. Besides, the two elements work in the same resonant mode and the same resonant frequency band when treated as radiators. In order to further explain the consistency in radiation and difference in reflection between the two structures, current distribution at 5.8 GHz is investigated in terms of radiation and reflection. Then, the two elements are arranged into a chessboard array to achieve the low scattering performance based on phase cancellation principle under the y-polarized incidence. Based on the absorption principle, the matching load is added to improve the scattering performance of the composite antenna array with the x-polarized incidence. Simultaneously, the proposed antenna array maintains good radiation characteristics due to the consistency between the radiation performances of the two elements. The corresponding antenna array is fabricated and tested. Simulated and measured results prove that the proposed antenna array also achieves good radiation performance. And a 6 dB radar cross section reduction is obtained from 5.6 to 6.2 GHz under the x polarization and from 5.5 to 7.0 GHz under the y polarization for the normal incident wave, implying 10.1% and 24% in relative bandwidth, respectively. In-band reflection suppression in the specular direction is demonstrated for an incident angle of 30° under both polarizations. The measured results are in good agreement with the simulated ones. Additionally, the approach proposed in this paper offers an effective way to deal with the confliction between radiation and scattering performance, and can also be applied to other kinds of antenna arrays.
Single-ion qubit with coherence time exceeding 10 minutes
Authors: Wang Ye , Zhang Jing-Ning , Kim Kihwan ,   Center for Quantum Information, Institute for Interdisciplinary Information Sciences, Tsinghua University, Beijing 100084, China
Published: December 2020

Quantum memory device capable of storing quantum information for a long period of time is one of the fundamental ingredients to realize large-scale quantum computation and quantum communication. Comparing with other quantum computation platforms, one of the advantages of the trapped-ion system is the long intrinsic coherence time. Before our work, the longest single-qubit coherence time in trapped-ion systems has been achieved to be less than 1 minute. It is discovered that the main limitation for the coherence time is the motional mode heating and the environment noise that includes the contributions from the magnetic field fluctuation and the phase noise of the microwaves. In a hybrid trapping system simultaneously trapping 171Yb+ and 138Ba+ ions, single-qubit quantum memories with coherence time longer than 10 minutes can be realized by applying sympathetic cooling and dynamical decoupling. This technique may have some value as the building blocks for quantum cryptography protocols and hybrid quantum computation platforms.
Research on fluorescence lifetime dynamics of quantum dot by single photons modulation spectrum
Authors: Zhang Qiang-Qiang  , Hu Jian-Yong  , Jing Ming-Yong  , Li Bin  , Qin Cheng-Bing  , Li Yao  , Xiao Lian-Tuan  , Jia Suo-Tang  ,   1. Institute of Laser Spectroscopy, State Key Laboratory of Quantum Optics and Quantum Optics Devices, Shanxi University, Taiyuan 030006, China;,   2. Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
Published: December 2020

Fluorescence lifetime is an important characteristic parameter of quantum dot, which plays an important role in studying the optical properties of quantum dot. As a common method to obtain fluorescence lifetime, fluorescence decay curve fitting has been broadly accepted. The least squares fitting to the fluorescence decay curve is performed by using the exponential decay function to obtain fluorescence lifetime with taking the instrument response function into account. However, since the fluorescence decay curve inevitably involves noise photons such as dark counts and stray photons, there is a certain error in the fluorescence lifetime obtained by the method. In order to reduce the error and improve the accuracy of the results, enough photons are required. Nevertheless, too many photons will result in low efficiency of lifetime analysis and temporal resolution, and therefore this method can hardly extract dynamic information on a smaller temporal scale. In this paper, we propose a new method of obtaining the fluorescence lifetime of quantum dot, namely the single photons modulation spectrum. The basic idea is based on the relationship between the fluorescence lifetime and the signal amplitude of pulse repetition frequency in a single dynamic process. The experimental results show that the fluctuation errors and deviation errors of lifetime obtained by our method are significantly lower than those of the previous method when the same number of photons is used. Therefore, high-accuracy fluorescence lifetime can be obtained. When the fluctuation error is 5%, the accuracy is increased by more than one order of magnitude. And to obtain the fluorescence lifetime of the same error level, the number of photons required for our method is much smaller than that of the previous one, which indicates that our method can effectively suppress the disturbance of noise photons and enables the lifetime measurement with high efficiency and temporal resolution. When the fluctuation error and deviation error are both 5%, the efficiency and temporal resolution are increased by more than four times. Finally, real-time lifetime trajectory corresponding to the photoluminescence intensity time trajectory is obtained by our method, where rich dynamic information can be obtained on a sub-second temporal scale. The method of obtaining fluorescence lifetime with powerful anti-noise capability, high efficiency and temporal resolution proposed in this paper can play an important role in studying the fluorescence dynamics of single quantum systems.
Intensity-dependent recollision dynamics in strong-field nonsequential double ionization
Authors: Huang Cheng , Zhong Ming-Min , Wu Zheng-Mao ,   School of Physical Science and Technology, Southwest University, Chongqing 400715, China
Published: December 2020

Using the three-dimensional classical ensemble model, we systematically investigate the strong-field nonsequential double ionization (NSDI) of He atom by intense linearly polarized laser pulses at different intensities for 750 nm and 1500 nm in wavelength. In the intensity range of 0.4−0.8 PW/cm2 considered in this work, for 750 nm wavelength the correlated electron pairs are always distributed mainly near the diagonal but for 1500 nm wavelength, with increasing laser intensity the population of electron pairs moves from the diagonal to the two axes, forming a near-axis V-shaped structure at 0.8 PW/cm2. The analysis indicates that for 750 nm with increasing laser intensity the contribution from the single-return events to NSDI decreases sharply and the contribution from the multiple-return events increases. For 1500 nm wavelength when the laser intensity increases, the contributions from one-, two- and three-return trajectories decrease and the contributions of other trajectories increase. It is because most of ionized electrons have a non-zero initial transverse momentum. After the excursion of the ionized electron, when it returns to the parent ion at the first time there is a distance in the transverse direction between the free electron and the parent ion, which hinders the recollision and NSDI from occurring. The transverse deviation can be significantly reduced by the Coulomb attraction from the parent ion to the free electron when it returns back to the parent ion in the longitudinal direction. Higher intensity results in larger returning velocity for the free electron. The free electron faster passes by the parent ion and the Coulomb attraction has less time to pull the free electron to the parent ion. For each return the compensation of the Coulomb attraction for the transverse deviation for high intensity is weaker than for low intensity. Thus for higher intensities more returns are required to compensate for the transverse deviation. Moreover, numerical results show the recollision distance in NSDI is smaller for the longer wavelength and higher intensity. It is attributed to the larger returning velocity of the free electron at the longer wavelength and higher intensity, which can more easily overcome the strong Coulomb repulsion between the two electrons and achieve a smaller recollision distance. Finally, electron correlation behaviors for those trajectories where recollision occurs with different return times are studied.
Quantum manipulation of entanglement enhancement in cascaded four-wave-mixing process
Authors: Yang Rong-Guo , Zhang Chao-Xia , Li Ni , Zhang Jing , Gao Jiang-Rui ,   College of Physics and Electronic Engineering, Shanxi University, Taiyuan 030006, China,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Shanxi University, Taiyuan 030006, China,   Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China,   Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
Published: December 2020

Entanglement manipulation in various systems is one of the important problems in quantum information science. In this paper, the phase sensitivity and entanglement enhancement of the cascade four-wave mixing of hot atomic steam are studied. The results show that the quantum entanglement of the probe light and the conjugate light output at the second level of the cascade four-wave mixing process is significantly stronger than that at the first level, and the maximum increment can reach more than 5 dB, and the perfect entanglement can be achieved by increasing the intensity factor. The relations of quantum correlation type and the size of the entanglement with the pump phase and the nonlinear intensity factor are also discussed in this work. The results show that because of the enhancement of entanglement and the sensitivity of entanglement type to pump phase, the light field noise characteristics can be changed by controlling the phase and intensity factors thus realize the enhancement of entanglement between the probe and coupling light and the quantum manipulation of entanglement extent and quantum entanglement type. The theoretical study is of important significance for guiding the experimental implementation of optical parameter manipulation of entanglement enhancement, compression angle and compression degree of two-mode compression state.
Experimental study on 1/f intrinsic thermal noise in optical fibers
Authors: Huang Jun-Chao , Wang Ling-Ke , Duan Yi-Fei , Huang Ya-Feng , Liu Liang , Li Tang ,   Key Laboratory of Quantum Optics and Center of Cold Atom Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Intrinsic thermal noise in optical fibers is an ultimate factor limiting the performances of fiber-based sensors and measurement systems. Therefore, it is important to have a thorough understanding of this kind of noise. However, the mechanism of the intrinsic thermal noise which has a 1/f spectral density remains unclear so far. There are two theoretical models to explain the mechanism of this kind of noise: thermoconductive noise model and thermomechanical noise model. The thermoconductive noise model states that the noise is caused by diffusion of local entropy fluctuations associated with random spontaneous emission events, while the thermomechanical noise model says that the noise is caused by spontaneous fluctuations of fiber length induced by mechanical dissipation. Which theoretical model is correct is still an open question. In this paper, we experimentally investigate the intrinsic thermal noise in optical fibers by using a balanced fiber Michelson interferometer with heterodyne detection technique. When a fiber-stabilized laser with ultralow frequency noise is used as a laser source and other noise sources are carefully controlled, the 1/f spectral intrinsic thermal noise can be observed down to infrasonic frequency. According to these measurements, in order to verify which theoretical model is the mechanism of generating the intrinsic thermal noise with 1/f spectral density, we study the relationship between the level of the intrinsic thermal noise and the concentration of the dopant in fibers and the applied tension of fibers. We observe that the level of the 1/f spectral intrinsic thermal noise is independent of the concentration of the dopant in fibers. This means that the thermoconductive noise model is not suitable to this case. We also observe that the level of the 1/f spectral intrinsic thermal noise can be reduced by increasing the tension exerted on the optical fibers. Because the mechanical loss of a fiber can be lower than the loss of the material which the fiber is made of when the fiber is subjected to a certain tension, this observation proves the fact that the 1/f spectral intrinsic thermal noise in optical fibers originates from the mechanical dissipation process inside optical fibers. This is consistent with the predictions of the thermomechanical noise model. Finally, the inconsistency between the experimental data and the theoretical results for thermomechanical noise is discussed.
Electrons leakage from upper laser level to high energy levels in active regions of terahertz quantum cascade lasers
Authors: Li Jin-Feng , Wan Ting , Wang Teng-Fei , Zhou Wen-Hui , Xin Jie , Chen Chang-Shui ,   Guangdong Provincial Key Laboratory of Nanophotonic Functional Materials and Devices, Guangzhou Key Laboratory for Special Fiber Photonic Devices, School of Information Optoelectronic Science and Engineering, South China Normal University, Guangzhou 510006, China,   Jiangmen Zhuxi Laser and Smart Co. Ltd., Jiangmen 529000, China
Published: December 2020

Terahertz quantum cascade laser is a semiconductor laser that effectively obtains terahertz waves. It uses the semiconductor heterojunction to have a quantum cascade effect under an applied voltage, and then the phonon assists the electron resonance from the upper stage to the next stage, so that a single electron injected externally can emit multiple photons. However, some electrons will deviate from the transport path during transportation and these electrons are called leakage electrons. Electron leakage comes from three ways. The first way is the scattering of electrons from the upper laser level through the long longitudinal phonon to the low energy level; the second way is the scattering of electrons from the lower laser level to the high energy bound level and the continuous level; and the third way is the scattering of electrons from the upper laser level to high energy bound levels and continuous levels. These leakage electrons directly reduce the number of population inversions in the laser system, making the laser output power limited. At present, most of researchers explain the electron leakage through indirect measurements, and there are few studies in which the electron leakage is analyzed by establishing theoretical models. In this paper, the electron leakage model in THz QCL is established by using thermodynamic statistical theory and laser output characteristic theory. The degree of electron leakage is measured by output power. The influence of lattice temperature and quantum well barrier height on electron leakage are studied. It is found that when the lattice temperature rises and the electrons in the upper laser state leak to higher energy levels, the number of electrons leaking to the adjacent bound state and the continuous state increases, and the number of electrons leaking to the next near-bound level is relatively small. In the case of electron leakage, the utilization of electrons becomes lowered, and the laser output power is also lowered. The study also shows that an appropriate increase in the height of the quantum barrier can suppress the leakage of electrons. Using the established theoretical model to optimize the quantum well barrier height of the previously reported laser system, an 8 mW terahertz quantum cascade laser (THz QCL) laser output at 210 K is obtained. Compared with the reported experimental results, the temperature and output power are improved. These results provide a theoretical basis for studying the electron leakage temperature characteristics of THz QCL and also optimally designing the THz QCL active region structure.
Impurity problem of alkaline-earth-like atoms near an orbital Feshbach resonance
Authors: Shi Yue-Ran , Lu Zhuo-Cheng , Wang Jing-Kun , Zhang Wei ,   Department of Physics, Renmin University of China, Beijing 100872, China,   Beijing Key Laboratory of Opto-electronic Functional Materials and Micro-nano Devices, Renmin University of China, Beijing 100872, China
Published: December 2020

In recent years, alkaline-earth and alkaline-earth-like atoms have attracted much research interest in the field of ultracold atom. Especially, the recently discovered orbital Feshbach resonance makes it possible to investigate a strongly interacting gas of alkaline-earth or alkaline-earth-like atoms, which has greatly enriched the scope of quantum simulation in these systems. This paper focuses on the impurity problem in a Fermi gas of 173Yb atoms near orbital Feshbach resonance. In this problem, the impurity atom in 3P0 state will interact with the background Fermi sea in the ground state and the molecule or polaron state will be produced out of the Fermi sea. By using the Chevy-like ansatz, we investigate the properties of the molecule and attractive polaron states firstly and a transition between these two states will be found. Then, some properties of the repulsive polaron state will be introduced, such as the effective mass and the decay rate. Furthermore, the effect of an additional Fermi sea will be considered in this system. Finally, we will discuss the impurity problem in a two-dimensional system.
Electronic structures and optical properties of Ce-doped anatase TiO2 with oxygen vacancy
Authors: Zhou Shi-Wen , Peng Ping , Chen Wen-Qin , Yu Ming-Huai , Guo Hui , Yuan Zhen ,   College of Materials and Chemical Engineering, Hainan University, Haikou 570228, China,   College of Materials Science and Engineering, Hunan University, Changsha 410082, China
Published: December 2020

 The crystal structures, defect formation energy, electronic structures and optical properties of oxygen vacancy and/or Ce-(co)doped anatase TiO2 are investigated by using density functional theory plus U calculations.

 The calculated results indicate that lattice distortion induces the enhanced octahedral dipole moment in Ce doped TiO2 crystal when introducing oxygen vacancy into the lattice of the TiO2 crystal, which is effective for separating the photo-excited electron-hole pairs; meanwhile, compared with the valence band of pure TiO2 and TiO2 mono-doped separately with Ce and oxygen vacancy, the valence band of TiO2 co-doped with Ce and oxygen vacancy broadens drastically, which is mainly contributed from the electronic states of Ce 5d, Ti 4s and O 2p in the valence band shifting toward the lower energy direction. As a result, Ce doped TiO2 with oxygen vacancy is beneficial to the mobility of photo-generated carriers in TiO2. Similarly, the anti-bonding states also move toward the lower band energy direction, which are formed by the mixture of Ce 4f, Ce 5d, Ti 3d, and O 2p orbits in the conduction band. Due to these shifts, the energy gap of Ce and oxygen vacancy codoped TiO2 is narrowed to 2.67 eV with the emerge of the occupied impurity energy levels near Fermi level. Because of the above-mentioned excellence features, the absorption spectra for doped systems exhibit remarkable red-shift, especially, the intensity of optical absorption of TiO2 co-doped with Ce and oxygen vacancy in the visible region and the infra-red region are obviously stronger than those of the Ce mono-doped TiO2.

 When introducing oxygen vacancy into the Ce-doped system, the calculated conduction band energy edge position changes from −0.27 eV to −0.32 eV, which implies that the reducing power of the conduction band edge of TiO2 is remarkably enhanced. More fascinatingly, the calculated band energy edges for the Ce and oxygen vacancy codoped TiO2 can satisfy the basic requirement for water splitting under visible light irradiation.

 In conclusion, Ce and oxygen vacancy co-doped system can effectively strengthen the photo-catalytic activity of TiO2 and improve the utilization of the solar light; and our calculated results provide a powerful theoretical basis for the applications of the Ce and oxygen vacancy co-doped anatase TiO2 in visible-light-driven water splitting in the future research.
Modeling information popularity dynamics based on branching process
Authors: Wu Lian-Ren , Li Jin-Jie , Qi Jia-Yin ,   School of Management, Shanghai University of International Business and Economics, Shanghai 201620, China,   College of Mathematics and Science, Shanghai Normal University, Shanghai 200234, China,   Key Laboratory of Trustworthy Distributed Computing and Service, Beijing University of Posts and Telecommunications, Beijing 100876, China
Published: December 2020

In the age of Web 2.0, modeling and predicting the popularity of online information was an important issue in information dissemination. Online social medium greatly affects the way we communicate with each other. However, little is known about what fundamental mechanisms drive the dynamical information flow in online social systems. To address this problem, we develop a theoretical probabilistic model based on branching process to characterize the process in which micro-blog information gains its popularity. Firstly, the data of information popularity and network structure of micro-blog network are analyzed. The statistical results show that the attenuation of information popularity follows a scaling law whose exponent is 1.8, and in-degree and out-degree of micro-blog network each also obey a power law distribution whose exponent is 1.5. The results of power law distribution show that there is a high-degree heterogeneity in a micro-blog system. The proportion of micro-blog information with popularity less than 100 is 95.8%, while the amount of micro-blog information with popularity more than 10, 000 is very small. The number of fans (in-degree) less than 100 accounts for 56.4%, while some users have millions of fans.Secondly, according to the design mechanism of the Weibo system, we assume that each user has two lists, i.e. a "home page list" and a "personal page list". Meanwhile, each user has two states at each moment: generating a new message with probability \begin{document}${\mu} $\end{document} to be sent out; 2) or forwarding the information already on the "personal page list" with probability \begin{document}$ (1-{\mu}) $\end{document} . Based on the assumptions, the information popularity model is proposed. Finally, the model is simulated. The simulation results show that the model can reproduce some features of real social network data, and the popularity of information is related to the network structure. By solving the model equation, the results of theoretical prediction are consistent with the simulation analyses and actual data.
Effect of rough inner wall of nanochannel on fluid flow behavior
Authors: Mei Tao , Chen Zhan-Xiu , Yang Li , Wang Kun , Miao Rui-Can ,   School of Energy and Environmental Engineering, Hebei University of Technology, Tianjin 300401, China
Published: December 2020

Flow system on a nano scale, as an effective and economic system, has been widely employed. While on a macroscopic scale, for the non-slip boundary, the velocity of the fluid at the surface is assumed to be consistent with the surface. This approximation may become invalid on a smaller length scale pertinent to the operation of microfluid devices. The interface slip effect has a significant influence on the flow because of its higher ratio of surface to volume. In this paper, the Poiseuille flow, which is composed of two infinite parallel asymmetric walls, is studied by the molecular dynamics method. The influence of wall roughness and surface wettability of channel on fluid flow in the channel are analyzed. The results show that the asymmetric upper and lower wall can lead to an asymmetric distribution of flow parameters. The change of wall roughness and wettability would affect the flow characteristics of fluid atoms near the wall. Due to the influence of wall grooves, the number density distribution near the rough wall is lower than that on the smooth wall side. As the rib height and wall wettability increase, the number density of fluid atoms in the groove increases gradually, and the change of the rib spacing does not substantially affect the number density distribution of fluid atoms near the rough wall. For different structure types of walls, the real solid-liquid boundary positions are determined by simulating the velocity field distribution in the channel under both Couette flow and Poiseuille flow, which can help us to better analyze the interface slip effect. The variation of wall roughness and wettability can affect the position of the solid-liquid interface. The change of rib height and wettability can greatly influence the velocity distribution in channel, and the position of the solid-liquid boundary as well. Conversely, the rib spacing has a less effect on the boundary position. The difference in boundary position can affect the interface slip effect. We can find the slip velocity and the slip length on one side of the rough wall to be smaller than those on the smooth wall side, and as the rib height and wall wettability increase, the slip velocity and the slip length significantly decrease near the rough wall side. The effect of rib spacing on fluid flow is trivial, and the interface slip velocity and length are relatively stable.
Equivalent circuit model and microwave reflection loss mechanism of double-layer spiral-ring metasurface embedded composite microwave absorber
Authors: Li Yu-Han , Deng Lian-Wen , Luo Heng , He Long-Hui , He Jun , Xu Yun-Chao , Huang Sheng-Xiang ,   School of Physics and Electronics, Central South University, Changsha 410083, China
Published: December 2020

High-performance absorbing material can play an important role in electromagnetic compatibility, electromagnetic radiation protection, and anti-detection of special equipment. Combining traditional absorbing material with metamaterial is an important direction for developing absorbing material. The composite absorbing body based on the development of metamaterial has advantages of thin thickness, light weight, strong absorption, and adjustable absorption band, but the super material absorption body composed of single-sized metal pattern elements possesses generally strong absorption only for electromagnetic waves at a certain frequency. It is difficult to meet the requirement for wide frequency absorption in practical applications. In order to broaden the absorption bandwidth of metamatial, metal spiral-ring metasurface coated short carbon fiber absorber with enhanced microwave absorbing performance is proposed. The absorber is a two-dimensional structure formed by periodically arranging a large number of individual absorber units in the horizontal and vertical direction. In the HFSS simulation software, a " master-slave boundary condition” consisting of " master boundary” and " slave boundary” is provided. Under this boundary condition, the electric field between adjacent boundaries has a phase difference, which can be used to simulate an infinite array. The research results show that the obvious enhancement of both the absorption peak and bandwidth can be observed by embedding the double-layer spiral-ring metasurfaces. The increase of initial length of spiral-rings and thickness of absorber are beneficial to further enhancing the microwave absorption. The reflection loss from 9.2 GHz to 18.0 GHz are under –10 dB (the bandwidth reaches 8.8 GHz), and the peak of S11 is –14.4 dB. Besides, we find that the effective electromagnetic parameters and impedance of spiral-ring metasurface embedded microwave absorber present obvious resonant phenomenon at multi-frequencies by calculating S parameters. Furthermore, an equivalent circuit model regarding double-layer spiral-ring embedded absorber is established to reveal the attenuation mechanism of microwave energy. The resonant frequencies derived from this model are well accord with the simulated results. Thereby, the multi-electromagnetic resonant frequencies make the composite microwave absorber combined with double-layer metal spiral-ring and carbon fiber have microwave reflection loss in a wide bandwidth.
Development on quantum metrology with quantum Fisher information
Authors: Ren Zhi-Hong , Li Yan , Li Yan-Na , Li Wei-Dong ,   Institute of Theoretical Physics, State Key Laboratory of Quantum Optics and Quantum Optics Devices, Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
Published: December 2020

Quantum metrology is one of the hot topics in ultra-cold atoms physics. It is now well established that with the help of entanglement, the measurement sensitivity can be greatly improved with respect to the current generation of interferometers that are using classical sources of particles. Recently, Quantum Fisher information plays an important role in this field. In this paper, a brief introduction on Quantum metrology is presented highlighting the role of the Quantum Fisher information. And then a brief review on the recent developments for i) criteria of multi-particle entanglement and its experimental generation; ii) linear and non-linear atomic interferometers; iii) the effective statistical methods for the analysis of the experimental data.
Research progress of crystalline silicon solar cells with dopant-free asymmetric heterocontacts
Authors: Zhao Sheng-Sheng , Xu Yu-Zeng , Chen Jun-Fan , Zhang Li , Hou Guo-Fu , Zhang Xiao-Dan , Zhao Ying ,   Institute of Photoelectronic Thin Film Devices and Technology of Nankai University, Tianjin 300350, China,   Key Laboratory of Photoelectronic Thin Film Devices and Technology of Tianjin, Tianjin 300350, China,   Engineering Center of Thin Film Photoelectronic Technology of Ministry of Education, Tianjin 300350, China,   Sino-Euro Joint Research Center for Photovoltaic Power Generation of Tianjin, Tianjin 300350, China
Published: December 2020

Due to the rapid development of dopant free asymmetric heterogeneous contacts in recent years, the theoretical conversion efficiency can reach 28%, which has large room for development and has attracted one’s attention. With the expectation of low cost and green pollution-free solar cell, the traditional crystalline silicon solar cell has many limitations due to its high equipment cost and flammable and explosive raw materials. It greatly increases the necessity of research and development of new solar cells with no doping and asymmetric heterogeneous contacts. The new solar cell is safe and environmental friendly due to the multi-faceted advantages of dopant-free asymmetric heterogeneous contact (DASH) solar cells constructed by transition metal oxide (TMO): the TMO has been widely studied as an alternative option, because of its wide band gap, little parasitic absorption, as well as repressed auger recombination, and conducing to the increase of the short-circuit current density of the solar cells; the DASH solar cell has high efficiency potential, its theoretical efficiency has reached 28%, and it can be produced by low-cost technology such as thermal evaporation or solution method; it always avoids using flammable, explosive and toxic gases in the manufacturing process. Our group proposed using MoOx as a hole selective contact and ZnO as an electron selective contact to construct a new and efficient DASH solar cell. It has achieved a conversion efficiency of 16.6%. Another device, in which MoOx is used as the hole selective contact and n-nc-Si:H as the electron selective, was fabricated, and its efficiency has reached 14.4%. In order to further speed up the research progress of the dopant-free asymmetric heterogeneous contact crystalline silicon solar cell, the development status is reviewed, and the basic principle and preparation technology of selective transport of transition metal oxide (TMO) carriers are discussed. And the effect of the hole transport layer, the electron transport layer and the passivation layer on the performance of the TMO dopant-free asymmetric heterogeneous contact (DASH) solar cells are discussed in order to have an in-depth understanding of the working mechanism and material selection of the battery, thereby providing guidance in preparing new and efficient DASH solar cells.
First-principles study of structural, elastic, thermodynamic, electronic and optical properties of cubic boron nitride and hexagonal boron nitride at high temperature and high pressure
Authors: Lü Chang-Wei , Wang Chen-Ju , Gu Jian-Bing ,   School of Materials and Chemical Engineering, Zhongyuan University of Tecnology, Zhengzhou 451191, China,   School of Computer Science and Technology, Henan Polytechnic University, Jiaozuo 454000, China
Published: December 2020

On the basis of the density functional theory of the first-principles, we employ the plane wave pseudopotential method and local density approximation to optimize the geometrical structure of cubic boron nitride and hexagonal boron nitride; then we study their mechanical properties, electronic structures and optical properties at zero temperature and zero pressure, and the thermodynamic properties at different temperatures and different pressures. By means of geometry optimization, we systematically investigate the elastic constant, bulk modulus, shear modulus, hardness and phonon spectrum for each of cubic boron nitride and hexagonal boron nitride. The results show that both cubic boron nitride and hexagonal boron nitride are structurally stable and brittle materials. Besides, cubic boron nitride is more stable than hexagonal boron nitride and it can be used as a superhard material. However, the thermal stability of hexagonal boron nitride is poor. The research results of electrical properties show that both cubic boron nitride and hexagonal boron nitride are indirect bandgap semiconductors, and the localization of cubic boron nitride is stronger than hexagonal boron nitride. The optical studies show that both cubic boron nitride and hexagonal boron nitride have good passivity to incident light. The c-BN is more sensitive to the incident light in high energy region. Last but not least, the thermodynamic properties of cubic boron nitride at high temperature and high pressure are also investigated. The relationships of thermodynamic expansivity, heat capacity, Debye temperature and Grüneisen parameter of c-BN with temperature and pressure are obtained. And the heat capacity of cubic boron nitride is found to be close to the Dulong-Petit limit at high temperatures. In this paper the relevant properties of cubic boron nitride and hexagonal boron nitride under high pressure are described theoretically, and a relatively reliable theoretical basis is provided for relevant experimental research.
Hawking tunneling radiation in Lorentz-violating scalar field theory
Authors: Yang Shu-Zheng , Lin Kai ,   Department of Astronomy, China West Normal University, Nanchong 637002, China,   Hubei Subsurface Multi-scale Imaging Key Laboratory, Institute of Geophysics and Geomatics, China University of Geosciences, Wuhan 430074, China,   Escola de Engenharia de Lorena, Universidade de Sao Paulo, 12602-810, Lorena, Brazil
Published: December 2020

In this paper, the Lorentz-violating scalar field equation is generalized in curved spacetime, and we find that the aether-like terms modify the scalar field equation, so that the effect can correct the properties near the event horizon of black hole spacetime. We then obtain the modified Hamilton-Jacobi equation by semi-classical approximation, and investigate the Hawking radiation and black hole thermodynamics in Schwarzschild black hole spacetime. The results show that the effects of aether-like terms increase the temperature of black hole, but reduce the entropy of black hole as \begin{document}${{ u}^\alpha } = {\text{δ}}_t^\alpha {u^t}, {\text{δ}}_r^\alpha {u^r}$\end{document}. This work can help to understand the properties of Lorentz-violating in curved spacetime.
Squeezing angle locking of entangled microwave based on photon counting
Authors: Wei Tian-Li , Wu De-Wei , Yang Chun-Yan , Luo Jun-Wen , Li Xiang , Zhu Hao-Nan ,   Information and Navigation College, Air Force Engineering University, Xi’an 710077, China
Published: December 2020

Quantum entanglement possesses important applications in quantum computation, quantum communication, and quantum precision measurement. It is also an important method to improve the performance of quantum radar and quantum radio navigation. However, the penetration of light wave is poor due to the high frequency, which leads to detecting limitations in bad weather. In this context, quantum entanglement in the microwave domain has been extensively studied, and it is hopeful to overcome the above-mentioned defects in quantum optics. Although the entangled microwave preparation of continuous variable is achievable at present, there exist still some problems such as poor entanglement performance, low entanglement efficiency, complex signal processing and control, which restrict the development of entangled microwave sources. In order to improve the entanglement performance in microwave domain, a squeezing-angle locking scheme based on single photon counting is proposed. First, two Josephson parametric amplifiers (JPAs) are driven respectively by two pump signals to generate two single-mode squeezed states which are uncorrelated to each other. Next, the squeezing angle difference between the two single-mode squeezed states is adjusted to 180°, and then the two signals are mixed in a superconducting 180° hybrid ring coupler for two entangled microwave outputs. The outputs are single photon detected, and the results are sent to the data processor for solution. The squeezing angle difference between the input single-mode squeezed microwaves is estimated by Bayesian criterion and compared with the target value to calculate the error. Finally, the squeezing angle correction information is fed back into the JPA pump to control the squeezing angle of the single-mode squeezed microwave of the JPA output as well as the relative squeezing angle to reach the target value. Thus, the dual-path entangled microwave with the optimal entanglement performance is output. Comparing with the existing entangled microwave preparation schemes, a single photon counter is utilized in the scheme of this paper, which leads to a detection efficiency of 90%. In addition, the Bayesian criterion is used to estimate the output result, and the theoretical precision reaches the quantum Cramer-Rao lower bound. Meanwhile, the introduced noise level and operation difficulty are reduced, which greatly improves the property of dual-path entangled microwave preparation.
Measurement-device-independent quantum key distribution under K-distributed strong atmospheric turbulence
Authors: Gu Wen-Yuan , Zhao Shang-Hong , Dong Chen , Zhu Zhuo-Dan , Qu Ya-Yun ,   Air Force Engineering University, Xi’an 710077, China,   National University of Defense and Technology, Xi’an 710006, China
Published: December 2020

Free-space quantum key distribution (QKD) allows two distant parties to share secret keys with information-theoretic security, which can pave the way for satellite-ground quantum communication to set up a global network for sharing secret message. However, free-space channels in the presence of atmospheric turbulence are affected by losses and fluctuating transmissivity which further affect the quantum bit error rate and the secure key rate. To implement free-space QKD, it is indispensable to study the effect of atmospheric turbulence. Different models have been used to describe the probability distribution for channel transmission coefficient under atmospheric turbulence, including the log-normal distribution and K distribution. In this paper, we focus on free space measurement-device-independent quantum key distribution (MDI-QKD) under K-distributed strong atmospheric turbulence. The MDI-QKD can close all loopholes on detection and achieve a similar performance to QKD, relying on time-reversed version of entanglement-based QKD protocol. Threshold post-selection method is adopted to restrain detrimental effects of the atmospheric turbulence, which is based on the selection of the intervals with higher channel transmissivity. By combining the general MDI-QKD system model with this method, we present a framework for the optimal choice of threshold. Our simulation result shows that the optimal threshold is dependent on the turbulence intensity and expected channel loss. Furthermore, compared with the original MDI-QKD protocols, the proposed protocol with threshold post-selection method can acquire a considerable better performance in key rate, especially in regions of high turbulence and high loss. What is more, this is instructive to the building of a practical free-space MDI-QKD system with better performance.
Dynamics studies of O+ + H2→ OH+ + H reaction
Authors: Yuan Mei-Ling , Li Wen-Tao ,   School of Opt-Electronic Engineering, Zaozhuang University, Zaozhuang 277160, China,   Department of Mathematics and Physics, BoHai University, Jinzhou 121000, China,   State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
Published: December 2020

In the present work, the long-range interaction potential part of potential energy surface (PES) of OH2+ system is revised and the new resulting PES apparently is more reasonable than the old one in the long-range part. Based on the new PES, the dynamics calculations of O+ +H2→ OH+ + H reaction are carried out at a state-to-state level of theory by using time-dependent quantum wave packet method with second order split operator in a collision energy range from 0.01 to 1.0 eV. The dynamic properties such as reaction probability, ro-vibrational resolved statereaction probability, integral cross section, differential cross section, and state specific rate constant are calculated and compared with available theoretical and experimental results. The results of ro-vibrational resolved state reaction probability reflect some dynamic properties such as resonances which is attributed to the deep well located on the reaction path. The vibrational resolved state reaction probability indicates that the excitation efficiency of the OH+ product is relatively low. The results of integral cross sections indicate that the present results are in better agreement with the experimental values than with previous theoretical calculations, especially in the low collision energy region. However, the state specific rate constant results underestimate the experimental values. The comparison betweenour calculations and the experimental results indicates that the contribution of the rotational excitation of H2 molecule should be included in the calculations. However, only the initial state v = 0, j = 0 is calculated in the present work. We suppose that the deviation of the present results from the experimental data is due to the fact that the rotational excitation of reactant isnot included in the present calculation. The differential cross section signals indicate that the complex-forming reaction mechanism isdominated in the case of low collision energy, but it transforms into abstract reaction mechanism as the collision energy further increases.