bluuebunny/crossref_metadata_2025 huggingface dataset:
Influences of PM2.5 atmospheric pollution on the performance of free space quantum communication
Authors: Nie Min  , Ren Jie  , Yang Guang  , Zhang Mei-Ling  , Pei Chang-Xing  ,   School of Communication and Information Engineering, Xi’an University of Posts and Telecommunication, Xi’an 710121, China;,   School of Electronics and Information, Northwestern Polytechnical University, Xi’an 710072, China;,   State Key Laboratory of Integrated Service Networks, Xi’an University of Electronic Science and Technology, Xi’an 710071, China
Published: December 2020

In recent years, the PM2.5 air pollution has been increasingly serious, which not only affects the air quality and visibility, but also has effects on free space optical signal transmission. However, the research about the relationship between the PM2.5 air pollution and the free space quantum communication has not yet been started. To investigate this relationship, the PM2.5 distribution function and its chemical extinction should be analyzed first. According to the degree of PM2.5 atmospheric pollution and the humidity of the atmosphere, the relationships among the PM2.5 index, the humidity of the atmosphere and the channel attenuation of the free space quantum communication can then be established. According to the amplitude damping channel and the depolarizing channel, the effects of the degree of PM2.5 air pollution on channel capacity, channel average fidelity, channel bit error rate are put out and simulated finally. Simulation results show that, if the air humidity is 30% and the PM2.5 index is 50, the channel capacity, channel average fidelity and the channel bit error rate of free space quantum communication will be 0.83, 0.91 and 0.0048 respectively. While the air humidity is 30% and the PM2.5 index is 300, the above channel parameters will be respectively 0.21, 0.56 and 0.0192. Further more, the channel average fidelity has an obvious difference between the two kinds of channel, and it is also related to the probability of the value of the source characters. Thus, the degree of PM2.5 air pollution has a significant effect on the performance of free space quantum communication. And, in order to improve the reliability of quantum communication in free space, the parameters should be adjusted adaptively based on the status of PM2.5 air pollution.
A two-dimensional coupled directed transport model
Authors: Wu Wei-Xia  , Song Yan-Li  , Han Ying-Rong  ,   Science Education Department, Beijing Institute of Graphic Communication, Beijing 102600, China;,   School of Science, Tianjin University, Tianjin 300072, China;,   School of Science, Hebei University of Technology, Tianjin 300401, China
Published: December 2020

Under the effect of external driving force and noise, a directed transport model for coupled particles in a two-dimensional potential is established. Here, a one-dimensional potential is taken as the periodic piecewise ratchet potential, and the other one is taken as the periodic symmetric non-ratchet potential to which the external periodic driving force and noise are applied. According to the nonequilibrium statistical theory and the nonlinear dynamics, the transport characters of the coupled system in the overdamped case are researched and discussed. Numerical results show that an obvious directed transport can appear both in the ratchet potential and in the non-ratchet potential case. But, the average velocities of the coupled system in the two potentials have completely different dependence on the system parameters. In the case of ratchet potential, the average velocity is strongly dependent on the coupling intensity, noise intensity, the driving strength, and the particle population; the average velocity can reach the maximum at appropriate coupling intensity, noise intensity, the driving strength or the particle population. Otherwise, in the case of non-ratchet potential, the average velocity is strongly dependent on the barrier height for the non-ratchet potential, but fluctuates as the coupling intensity, the driving strength, the driving initial phase difference or the particle population varies. This shows that the average velocity of the coupled system in the non-ratchet potential has weak dependence on system parameters, including the coupling intensity, the driving strength, the driving initial phase difference and the particle population.
Influence of slow wave structure explosive emission on high-power surface wave oscillator
Authors: Zhao Wen-Juan  , Chen Zai-Gao  , Guo Wei-Jie  ,   College of Medicine and Forensics, Key Laboratory of Forensic Sciences, Ministry of Health, Xi’an Jiaotong University, Xi’an 710061, China;,   School of Electronic and Information Engineering, Xi’an Jiaotong University, Xi’an 710049, China
Published: December 2020

As the working frequency of a vacuum electron device reaches the terahertz frequency band, the cross section of the surface wave oscillators (SWO) becomes very small, and the micro-fabrication precision of the device cannot be guaranteed, at the same time, because the electromagnetic field of SWO concentrates on the inner surface in slow wave structure, when the working voltage of surface wave oscillator is very high, the explosive emission probability of the slow wave structure increases greatly, and the explosive emission can influence the working characteristic of the device. This paper analyses the distributing property of the electrical field in the slow wave structure of 0.14 THz SWO. Parameters of the SWO under study are as follows: working voltage is 312 kV, explosive emitted current is 1.67 kA, periodic length of the slow wave structure is 0.7 mm, width of the slot is 0.4 mm, and the height of it is 0.3 mm; cold-test results indicate that the amplitude of the electrical field in the slow wave structure varies sinusoidally; the amplitude of the electrical field reaches a maximum value in the middle of the slow wave structure near its inner surface, and the explosive electron emission can occur most possibly in this position, because the electrical field in the slow wave structure varies with very high working frequency. The explosive emitted electron may bombard back the slow wave structure, and the secondary electrons will be emitted at a certain probability, for which the formula proposed by Vaughan is used to compute the secondary emission yield, and this formula is implemented in the self-developed particle-in-cell code UNIPIC; while the code is used to simulate 0.14 THz SWO with explosive emission in the slow wave structure. In the simulation, the slow wave structure multipactor discharge induced by electrons is also considered; the phase space of the electrons emitted from the slow wave structure shows that the energy of secondary electrons is below 5 keV, so the validity for secondary electron yield is affirmed. Numerical simulation results indicate that because the emitted electrons from the slow wave structure change the distribution character of the electrical field in the slow wave structure, especially the amplitude of the electrical field in the middle of the slow wave structure, the beam-wave interaction is weakened, and as a result, output power decreases from about 22.6 megawatts to only 1.89 megawatts.
High sensitive photoassociation spectroscopy investigation on 0u+ (6P3/2) long-range state of ultracold cesium molecules
Authors: Ma Jie  , Wang Xiao-Feng  , Xin Tong-Yu  , Liu Wen-Liang  , Li Yu-Qing  , Wu Ji-Zhou  , Xiao Lian-Tuan  , Jia Suo-Tang  ,   State Key Laboratory of Quantum Optics and Quantum Optic Devices, Institute of Laser Spectroscopy, College of Physics and Electronic Engineering, Shanxi University, Taiyuan 030006, China
Published: December 2020

Photoassociation spectroscopy with high resolution for 0u+(6P3/2) long-range state of ultracold cesium molecules has been measured experimentally using the modulated trap loss fluorescence spectroscopy technology. The spectral range has been extended over 60 cm-1 below the 6S1/2 + 6P3/2 dissociation limit as compared with other groups. twenty-five new observations of the Cs2 0u+ in long-range state are reported. The vibrational binding energies of these states are analyzed by using the LeRoy-Bernstein formula. The long-range parameter C3 in molecular 0u+(6P3/2) state is derived for 16.1030.010, and the corresponding molecular potential curve is depicted.
Characteristics and parameter optimization of electron beam radiography
Authors: Chen Yuan  , Wang Xiao-Fang  , Shao Guang-Chao  ,   Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China
Published: December 2020

The electron beam produced by an ultra-short, high-intensity laser pulse is of properties of small source size, short duration, and quasi-monoenergetic energy, and will play a unique role in radiographic diagnostics. By analyzing the scattering processes of electrons in materials and performing Monte-Carlo simulations, electron radiography for probing target surface non-uniformities or material interfaces is studied for electron energy ranging from 100 keV to several hundreds of MeV, and the results are compared with those of proton radiography and X-ray radiography, respectively. Features and parameter optimization of electron radiography are obtained, and some applications are suggested. By taking advantage of inelastic scattering or energy loss of charged particles, target surface nonuniformities could be diagnosed by a charged-particle beam whose range is close to the target thickness. Such a diagnosis would produce a higher detection contrast than that by absorption-type X-ray radiography. For a proton beam, a target thickness variation as small as 0.1% could be detected due to a more evident Bragg peak of the stopping power near its range. Nevertheless, the energy of laser-accelerated proton beams being up to 100 MeV would limit the applications. For an electron beam, since a thickness variation of 0.3% could be detected, its energy over 1 GeV has been realized by laser acceleration, the electron radiography could be extended to diagnose thicker targets. When using an electron beam to radiograph a thin or a foil target, for example, of thickness on the order of 100 μm, a spatial resolution of 11 μm or better could be achieved due to the reduced elastic scattering and angular deflection. By taking advantage of elastic scattering of electrons, an electron beam whose range is much greater than the target thickness could be used to diagnose a target interface composed of different materials or even a multilayered capsule, and a higher contrast of the electron fluence modulation at interfaces would be realized than that by absorption-type X-ray radiography, which is caused by stronger scattering of electrons as the electron scattering cross section is several orders of magnitude greater than that of X-ray scattering such as the Thomson scattering. As a laser-produced electron beam is prone to have an ultrafast pulse duration of 100’s of femtoseconds or less, it is anticipated that the electron radiography will produce an ultrasfast temporal resolution. These results and conclusions would be helpful to the applications and parameter optimization of electron radiography.
Study on damage mitigation for dielectric mirrors by using femtosecond laser micromachining
Authors: Lin Yuan-Yuan  , Jiang You-En  , Wei Hui  , Fan Wei  , Li Xue-Chun  ,   National Laboratory on High Power Laser and 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

Electric field distribution, in the wavelength range 1053 nm and 0° high reflection coatings, with different truncated conical pits has been estimated by using the finite difference time domain method (FDTD). Results of simulations indicate that the smaller the angle between the pit’s edge and the normal line, the higher the damage threshold of the mitigation pit. In the experimental process, the dimension of this angle mainly depends on two factors, i.e. the influencing area of the focal spot and the depth of mitigation pits. Because the ratio between them is the angle’s tangent, decreasing the influencing area of the focal spot and increasing the depth of the machined area could yield a mitigation pit with a smaller angle. By optimizing the focal spot size, pulse energy, step size and the number of machining passes of femtosecond laser micromachining, a pit with an angle of 25° and a depth of 14 μm is obtained. The typical damage threshold of the mitigation pit is about 21 J/cm2, which is 2.3 times greater than the fluence-limited defect. Moreover, the laser damage testing results of 50 mitigation pits show that the mitigation process has a good repeatability. The correlation between the cone angle and the damage threshold is also examined, the simulations are in agreement with the experimental results. The ratio of the maximum intensification between 45° and 25° cone angles is ～2.5 and that of the damage threshold between the two angles is ～0.5. At the same time, the relationship between the micromachining pulse width and the damage threshold is also estimated: if other process parameters are kept constant, a longer pulse length tends to produce lower laser-resistant mitigation pits. Compared to the result of 260 fs laser pulse, the truncated conical pit created by 6 ps laser pulse has a smaller depth, which implies that more thermal effect occurs during the miromachining process. However, cracks are not found around the pit. Thus, thermal damage is not the major reason for the decrease of damage threshold. Meanwhile, smaller depth also indicates that the pit has a large cone angle. According to the result of former FDTD simulation, the decrease of damage threshold is mainly caused by electric field enhancement in a pit with a large cone angle.
A nano-silicon-photonic switch driven by an optical gradient force
Authors: Lin Jian-Xiao  , Wu Jiu-Hui  , Liu Ai-Qun  , Chen Zhe  , Lei Hao  ,   School of Mechanical Engineering, Xi’an Jiaotong University, Xi’an 710049, China;,   State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi’an Jiaotong University, Xi’an 710049, China;,   School of EEE, Nanyang Technological University, Singapore 639798
Published: December 2020

Using light to dynamically and stably redirect the flow of another beam of light is a long-term goal for photonic-integrated circuits. However, it is challenging to realize a practically all-optical switching device in silicon owing to its weak optical nonlinearity. Major published work on all-optical switches were using single-photon absorption and two-photon absorption, which requires ultrahigh switching energy. This paper presents a nano-silicon-photonic all-optical switch driven by an optical gradient force, in which a fast switching speed with low power consumption is obtained. Each switching element is composed of a waveguide crossing connection and a micro-ring resonator. The ring resonator is side-coupled to a double-etched waveguide crossing, while the micro-ring resonator is partially released from the substrate and becomes free-standing. When the “drop” port is in “OFF” state, the wavelength of the signal light from the “input” port does not satisfy the resonant condition in the micro-ring. Therefore, light is mainly transmitted to the "thru" port without control light. When a control light is loaded to the “add” port, of which the wavelength satisfies the resonance condition in the micro-ring, a strong optical gradient force is generated by the induced evanescent optical field. The freestanding arc of the ring is then bent down to the substrate, leading to a cavity resonance wavelength shift. As a result, the signal light is diverted to the “drop” port and the corresponding transmission state is switched to the “ON” state. The optical switch is fabricated by nano-photonic fabrication processes using standard silicon-on-insulator (SOI) wafer. The waveguide structures have a width of 450 nm and a height of 220 nm for a single mode transmission; the outer radius of the ring in the switching element is 15 μm; the coupling gap between the ring and the nano-waveguide is 200 nm; the system is fabricated through two-step lithography and plasma dry etching processes while the free-standing arc is released by undercutting the buried oxide layer. #br#A switching time of 180 ns(rise) and 170 ns (fall) is experimentally demonstrated, which is much faster than that of conventional optical switches. The present optical switch can reach a high extinction ratio (10.67 dB) and a low crosstalk (-11.01 dB). In addition, the proposed switch has the advantages of compact size and low power consumption. Potential applications of this optical switch include photonic integrated circuits, signal processing, and high speed optical communication networks.
Study on planar concave diffraction grating with Bragg reflector facets
Authors: Li Bao  , Du Bing-Zheng  , Zhu Jing-Ping  ,   Shaanxi Key Laboratory of Information Photonic Technique Key Laboratory for Physical Electronics and Devices of the Ministry of Education School of Electronic and Information Engineering, Xi’an Jiaotong University, Xi’an 710049, China
Published: December 2020

Based on the fact that Bragg reflection grating(BRG) is a special one-dimensional photonic crystal, we propose to apply the one-dimensional photonic crystal band gap theory to the design of Bragg reflection grating and then to make an analysis of its optical performance. According to the above band gap theory, FDTD solution is used to build the elliptical Bragg etched diffraction grating (EDG) based on the Rowland circle. We have studied the spectral characteristics for both TE and TM modes and the angle dispersion due to the variation of the incident angle, at the same time, the optical performances in the air dielectric type Bragg grating and the Al metallic line type Bragg grating are also made to compare with each other. It turns out that by choosing appropriate parameters the diffraction efficiency can be got more than 95% within the scope of 1.465-1.615 μm in both TE and TM modes, and the air dielectric type Bragg grating structure behaves better in the uniformity throughout the whole channel than in the Al metallic line type Bragg grating structure. When the incident angle varies from 30° to 60°, the angle dispersion in TM mode is larger than that in TE mode. This is the foundation of a new type of EDG wavelength division multiplexer with advantages of small size and high diffraction efficiency. It may have the potential to promote the development of high diffraction efficiency dense wavelength division multiplexer in the future.
Design of a terahertz even splitter and its tolerance analysis
Authors: Huang Hai-Xuan  , Xu Ping  , Ruan Shuang-Chen  , Yang Tuo  , Yuan Xia  , Huang Yan-Yan  ,   College of Electronic Science and Technology Shenzhen University Shenzhen 518060, China;,   Institute of Micro-Nano Optoelectronic Technology, Shenzhen University, Shenzhen 518060, China
Published: December 2020

A novel method is presented in this paper to realize terahertz even beam splitting by using a subwavelength binary simple periodic rectangular structure, for making comprehensive application of both the RCWA (Rigorous Couple-Wave Analysis) and the GA (Genetic Algorithm). By applying RCWA, the efficiency of each diffraction order can be numerically solved by using the structure parameters. To design an even beam splitter with a subwavelength structure is to find the optimal duty cycle f, period d, the grating depth h1 and the substrate thickness h2 to approach the minimum zero-order diffraction efficiency, the maximum sum of each non-zero-order diffraction efficiency, and the uniform distribution. Considering the three goals above, an evaluation function is established. GA is applied to optimize the evaluation function F, and then the optimal parameters of the splitter are obtained. When its period, groove depth, substrate thickness and duty ratio respectively equal to 269.7 μm, 175.2 μm, 18.1 μm and 0.409, the normal-incident TE-polarized terahertz plane wave with its frequency equal to 2.52 THz is divided evenly into the diffraction orders±1 and±2. It has a total efficiency up to 92.23% with a preferable result of reducing zero-order diffraction efficiency to 0.192% and an error of uniformity down to 6.51×10- 6, indicating an excellent performance of diffraction efficiency, uniformity and zero-order suppression as a terahertz even splitter. These results break the limitation of realizing even beam splitting in which the traditional scalar theory applies. In addition, this paper exposes the law of influence of the structure parameters, including ridge width, groove width, groove depth, duty ratio and substrate thickness, on the diffraction efficiency and its uniformity. It is found that only a small deviation of the structure parameters, corresponding to a deviation of ridge width a, groove width b, groove depth h1, and substrate thickness h2, less than 1 μm from the optimum design values, the element maintains good beam splitting performance. P0 is permitted to suppress to less than 2%, the error of uniformity U is better than 19.60%, and the diffraction efficiency maintains higher than 79.10%. With a substantial deviation from the design values of the structure parameters, the performance of the splitter will severely degrade and need to be redesigned.
Analysis of decoupling mechanism of an acoustic coating layer with horizontal cylindrical cavities
Authors: Huang Ling-Zhi  , Xiao Yong  , Wen Ji-Hong  , Yang Hai-Bin  , Wen Xi-Sen  ,   Vibration and Acoustics Research Group, Laboratory of Science and Technology on Integrated Logistics Support, and College of Mechatronic Engineering and Automation, National University of Defense Technology, Changsha 410073, China
Published: December 2020

Introducing the decoupling coating is an effective way to reduce sound radiation from underwater structures. In order to investigate the decoupling mechanism of a viscoelastic coating layer with horizontal cylindrical cavities, such a coating layer is approximated to a homogeneous layer with equivalent material properties, and a theoretical model is also developed to predict the sound radiation from a finite plate with such a decoupling coating layer. #br#The validity of the theoretical model is confirmed by comparison with the finite element method; and the decoupling mechanism of the coating layer is discussed. Numerical analysis shows that: (1) The energy flow across the interface between the plate and coating layer is mainly conveyed by longitudinal waves. (2) At a low frequency, the coating layer has nearly no decoupling effect. (3) In contrast with a homogeneous coating layer, the coating layer with horizontal cavities can greatly enhance the mechanical impedance in the mid- and high-frequency areas; hence the mean square velocity is effectively suppressed in the same area. (4) Compared with the homogeneous coating layer, the coating layer with horizontal cavities has a larger impedance mismatch with water, thus it exhibits great vibration transmission loss. Therefore, in general, the coating layer with horizontal cylindrical cavities has a better decoupling performance than the homogeneous coating layer in the mid- and high-frequency areas.
Effect of Cu on the structure and phase-change characteristics of Sb2Te film for high-speed phase change random access memory
Authors: Wang Dong-Min  , Lü Ye-Gang  , Song san-Nian  , Wang Miao  , Shen Xiang  , Wang Guo-Xiang  , Dai Shi-Xun  , Song Zhi-Tang  ,   Faculty of Information Science and Engineering, Ningbo University, Ningbo 315211, China;,   Shanghai Institute of Micro-system and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China;,   Infrared Material and Device Laboratory of High Tech Research Institute, Ningbo University, Ningbo 315211, China
Published: December 2020

In this paper, in-situ X-ray diffratometer, Raman spectrometer, and X-ray reflectometer are employed to study the crystal structure, bonding states, and density change upon crystallization of Cu-Sb2Te films. It is shown that the crystallization temperature increases with increasing Cu content due to much more energy being required to overcome the rigid atomic network for the atoms rearrangement as a result of the complex branching and cross links. In X-ray diffraction pattern, both hexagonal Cu7Te4 and Sb2Te peaks have nearly the same peak positions, while the rhombohedral Sb peaks shift obviously their positions toward a small angle upon heating, suggesting a significant increase in lattice parameters of Sb phase. A Cu-Te bond is formed in Sb2Te films containing 10 at% and 14 at% Cu which are crystalized into hexagonal Cu7Te4, rhombohedral Sb and hexagonal Sb2Te three phases. When Cu concentration increases to 19 at%, Cu-Te bond becomes full, and the excess of Cu will bond with Sb. Compared with Ge2Sb2Te5 (GST), Sb2Te films with 10 at% and 14 at% Cu have lower density changes upon crystallization which are about 3.2% and 4.0%, respectively. Phase change random access memory (PCRAM) based on Cu-Sb2Te is successfully fabricated and characterized. Operations of set-reset can be realized in a 10 ns pulse for Cu-Sb2Te based PCRAM. The value of set and reset operation voltage decreases with increasing Cu content. The endurance test shows that the operation cycle numbers can reach 1.3×104 and 1.5×105 for the 10 at% and 14 at% Cu-based PCRAMs, respectively. The resistance ratio of reset and set states maintains a balance of about 100. Cu-Sb2Te film may be considered as one of the promising candidates for high-speed PCRAM.
Generation of six-photon hyperentangled states
Authors: Ding Dong  , He Ying-Qiu  , Yan Feng-Li  , Gao Ting  ,   Department of Basic Curriculum, North China Institute of Science and Technology, Beijing 101601, China;,   College of Physics Science and Information Engineering, Hebei Normal University, Shijiazhuang 050024, China;,   College of Mathematics and Information Science, Hebei Normal University, Shijiazhuang 050024, China
Published: December 2020

Nowadays, the nonlinear optical process of spontaneous parametric down-conversion is considered as the canonical approach for creating entangled-photon pairs. We consider three pairs of entangled photons emitted by the parametric down-conversion source, and introduce a setup for evolving these photons based on linear optics, which is composed of several polarizing beam splitters, beam splitters, and half wave plates. By using the parametric down-conversion source and the setup, we carefully design an efficient scheme for preparing six-photon hyperentangled states in both the polarization and the spatial degrees of freedom. Because we use almost all possible behaviors of the three pairs of entangled photons, the present scheme is efficient for creating six-photon hyperentangled states. Next, in the regime of weak nonlinearity we design a quantum nondemolition detection to distinguish the two cases of photons in two special spatial modes. It is worth pointing out that our scheme is much easier to realize, since the strength of the nonlinearities in the process of quantum nondemolition detection can be restricted to the scalable orders of magnitude in practicality.
Optimizing quantum state transfer in multi-excitation spin chains via information flux
Authors: Chen Jun  , Yu Ya-Fei  , Zhang Zhi-Ming  ,   Laboratory of Nanophotonic Functional Materials and Devices (SIPSE), Laboratory of Quantum Engineering and Quantum Materials, South China Normal University, Guangzhou 510006, China
Published: December 2020

The transfer of quantum states between distant nodes is one of the most fundamental tasks in quantum-information processing. Recent studies show that the antiferromagnetic spin chain initially prepared in a multi-excitation state can provide suitable pathways for quantum state transfer. In this paper, we investigate the quality of state transfer through a uniformly coupled antiferromagnetic spin chain where the initial state of the channel varies with the number of spin excitations. Firstly, by analyzing the dynamics of observables for the output qubit using the information-flux approach, the explicit relation about how the average fidelity of state transfer depends on the initial state of the spin channel is obtained. The results show that the average fidelity of state transfer through a multi-excitation spin channel only relates to the parity of the number of spin excitations in the channel. Then we compare the maximum average fidelity of state transfer through the odd-excitation with those through the even-excitation spin channels, and provide a simple criterion to optimize the quality of state transfer by choosing appropriate channels from the odd-excitation and the even-excitation channels. Compared with the previous studies which initialize the chains into the ground state of the ferromagnetic medium or the Nel state, the maximum average fidelity of state transfer is evidently enhanced by using the optimized channel. Moreover, we analyze the entanglement distribution through the channel having different number of spin excitations via the information-flux approach. It is found that the quality of entanglement distribution not only relates to the number of initial spin excitations present in the channel, but also depends on the initial ordering of these excited spins. The numerical results suggest that the amount of distributed entanglement and duration of distribution in the channel where all spins are down or up are larger than those in other excited channels. Based on these results, we can choose appropriate quantum channels for state transfer and entanglement distribution in practice.
Quantum network direct communication protocol over noisy channel
Authors: Ma Hong-Yang  , Qin Guo-Qing  , Fan Xing-Kui  , Chu Peng-Cheng  ,   School of Sciences, Qingdao Technological University, Qingdao 266033, China;,   Department of Physics, Tsinghua University, Beijing 100084, China
Published: December 2020

The direct communication protocol of quantum network over noisy channel is proposed and investigated in this study. In communication process, all quantum nodes share multiparticle Greenberger-Horne-Zeilinger (GHZ)-states. The sending node takes the GHZ-state particle in the hand as the control qubit and the particle for sending secret information as the target qubit, which carries out the CNOT gate operation for the control and target qubit. Each receiving node takes the GHZ-state particle in the hand as the control qubit and the particle of the received secret information as the target qubit, in which the CNOT gate operation is repeated to obtain the secret information that contains the bit error. Each receiving node uses the extracted part of qubits as the checking qubits, and then corrects the bit-flip errors using parity check matrix together with the rest part of qubits. As a result, all receiving nodes obtain rectified secret information. In addition to the high security analysis, this study also presents the detailed analyses of the throughput efficiency and the communication performance.
Quantum secure direct communication
Authors: Li Xi-Han  ,   College of Physics, Chongqing University, Chongqing 401331, China;Department of Physics and Computer Science, Wilfrid Laurier University, Waterloo N2L3C5, Canada
Published: December 2020

Quantum secure direct communication (QSDC) is one of the most important branches of quantum communication. In contrast to the quantum key distribution (QKD) which distributes a secure key between distant parties, QSDC directly transmits secret message instead of sharing key in advance. To establish a secure QSDC protocol, on the one hand, the security of the quantum channel should be confirmed before the exchange of the secret message. On the other hand, the quantum state should be transmitted in a quantum data block since the security of QSDC is based on the error rate analysis in the theories on statistics. Compared with the deterministic quantum key distribution (DQKD) which can also be used to transmit deterministic information, QSDC schemes do not need extra classical bits to read the secret message except for public discussion. In this article, we introduce the basic principles of QSDC and review the development in this field by introducing typical QSDC protocols chronologically. The first QSDC protocol was proposed by Long and Liu, which can be used to establish a common key between distant parties. In their scheme, the method for transmitting quantum states in a block by block way and in multiple steps was proposed and the information leakage before eavesdropping detection was solved. Subsequently, Deng et al. presented two pioneering QSDC schemes, an entangled-state-based two-step QSDC scheme and a single-photon-state-based quantum one-time pad scheme, in which the basic principle and criteria for QSDC were pointed out. From then on, many interesting QSDC schemes have been proposed, including the high-dimension QSDC scheme based on quantum superdense coding, multi-step QSDC scheme based on Greenberger-Horne-Zeilinger states, QSDC scheme based on quantum encryption with practical non-maximally entangled quantum channel, and so on. We also introduce the anti-noise QSDC schemes which were designed for coping with the collective-dephasing noise and the collective-rotation noise, respectively. In 2011, Wang et al. presented the first QSDC which exploited the hyperentangled state as the information carrier and several QSDC schemes based on the spatial degree of freedom (DOF) of photon, single-photon multi-DOF state and hyperentanglement were proposed subsequently. In addition to the point-to-point QSDC schemes, we also review the QSDC networks. Finally, a perspective of QSDC research is given in the last section.
Rydberg-atom-based electrometry
Authors: Huang Wei  , Liang Zhen-Tao  , Du Yan-Xiong  , Yan Hui  , Zhu Shi-Liang  ,   Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials, School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510006, China;,   National Laboratory of Solid State Microstructures, School of Physics, Nanjing University, Nanjing 210093, China
Published: December 2020

Atom in Rydberg state has large polarizability, large electric dipole and low ionization threshold field. It is very sensitive to electric field, therefore it can be used to measure the amplitude of electric field, especially the microwave electric field. The new developed scheme is based on quantum interference effects (electromagnetically induced transparency and Autler-Townes splitting) in Rydberg atoms. Instead of the direct amplitude measurement, this method tests the Rabi frequency value of the transmission spectrum which is determined by the microwave electric field strength and the corresponding atom nature. The minimum measured strengths of microwave electric fields are far below the standard values obtained by traditional antenna methods. Compared with the traditional methods, this new scheme has several advantages, such as self-calibration, non-perturbation to the measured field and independence of the probe length. Besides, this scheme can also be used to measure the polarization direction of microwave electric field and realize sub-wavelength imaging. Through adjusting the wavelength of coupling laser, a broadband 1-500 GHz microwave electric field measurement can be achieved. This new scheme is benefitial to conducting the continue electric field measurement and the miniaturization of the test equipment. In this paper, the researches about using Rydberg atom to measure electric field with high precision are reviewed. The basic theory and experimental techniques are introduced. Finally, we discuss a promising method of using Rydberg atom interferometer to detect the accumulated phase in the process of interaction between electric field and Rydberg atoms. This method converts amplitude measurement into phase test, which may improve the precision and sensitivity.
Ordered detection of layered space-time signals based on the propagation delays of underwater acoustic channels
Authors: Zhang Xin  , Xing Xiao-Fei  , Zhang Xiao-Ji  , Zhou Yan-Qun  , Zhao Shun-De  , Li Jun-Wei  ,   School of Marine Science and Technology, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

The multiple-input multiple-output (MIMO) architecture with the layered space-time codes is a very promising solution for the high data rate underwater acoustic communications. The realization of this potential advantage, however, needs the essential layered space-time signal processing methods for canceling the interference resulting from the multipath propagation and the asynchronous arrivals of the sub-streams due to the different propagation delays, and the interference between the transmitted streams superposed in each receiving hydrophone. In this paper, the low-complex layered space-time signal detection scheme for the underwater acoustic communications is investigated. A propagation delay-based ordered successive interference cancellation (OSIC) algorithm is proposed at first. Sub-streams are sorted at the receiver according to the arrival orders resulting from the relative propagation delays inherent in the underwater acoustic channels from the transmitting transducers to the receiving hydrophones. The sub-stream with the first arrival is detected first. The proposed OSIC algorithm based on the "first-come first-go" principle has an advantage in the reduction of the interference from yet-to-be-detected sub-streams, therefore improving the detection performance at each step. The analysis manifests that the delay-based ordering is an optimal detection ordering to minimize the probability of overall block error for the asynchronous space multiplexing architectures. Then the ordering procedure is given which is performed by estimating the relative delays between the MIMO channels and requires only one ordering before the signal detection. This channel estimation-based method simplifies dramatically the ordering procedure and the calculations, therefore reducing substantially the calculation complexity of the layered signal detection. Finally, the single-carrier frequency domain equalization is employed to compensate for the multipath interference and the asynchronous arrival interference from the underwater acoustic propagation. Numerical results show that the performance gain can be obtained with the delay-based OSIC detection algorithm relative to the detection without ordering; moreover the gain increases substantially with the data rate. The investigation results demonstrates, on the other hand, that the inherent relative propagation delay in the underwater acoustic channels leading to asynchronous interference to the signal detection can be turned into an advantage to improve the performance with the efficient space-time signal processing algorithms.
Effects of Cu doped ZnO diluted magnetic semiconductors on magnetic and electrical performance from simulation and calculation
Authors: Hou Qing-Yu  , Xu Zhen-Chao  , Wu Yun  , Zhao Er-Jun  ,   College of Sciences, Inner Mongolia University of Technology, Hohhot 010051, China;,   Chemistry Department, Inner Mongolia Vocational College of Chemistry Engineering, Hohhot 010071, China
Published: December 2020

At present, the effects on the magnetic and electrical properties of Cu heavily doped ZnO with the mole amount of Cu being in a range of 0.02778-0.16667 are rarely studied by first-principles. Therefore two models for Zn1-xCuxO supercells (x=0.02778, 0.03125) are set up to calculate the band structures and density of states by using the plane-wave ultrasoft pseudopotential based on the spin-polarized density functional theory. The calculation results indicate that the doped systems are degenerate semiconductors, and they are semimetal diluted magnetic semiconductors. As the doping amount of Cu increases, the relative concentration of free holes increases, the effective mass of holes decreases, the electron mobility decreases and the electronic conductivity increases. These results are validated again by the analysis of ionization energy and Bohr radius, and they are consistent with the experimental data. As the doping amount of single-Cu increases from 0.02778 to 0.0625, the volume of doping system decreases, the total energy increases, the stability decreases, the formation energy increases and doping is more difficult. As the same concentration and the different doping modes for double-Cu doped, the magnetic moment of doping system first increases and then decreases with the increasing of spacing of Cu-Cu; while the bonds of nearest Cu–O–Cu lie along the a-axis or b-axis, the magnetic moment of doping system disappears; while the bonds of nearest Cu–O–Cu lie along the c-axis, the Curie temperature reaches a temperature above room temperature. As the doping amount of double-Cu increases from 0.0625 to 0.16667, the total magnetic moment of doping system first increases and then decreases, while the bonds of nearest Cu–O–Cu lie along the c-axis. The calculation results are consistent with the experimental data.
Asymmetric giant magnetoimpedance of Co-rich melt-extraction microwires
Authors: Zhang Shu-Ling  , Chen Wei-Ye  , Zhang Yong  ,   School of Mechanical Engineering, Ningxia University, Yinchuan 750021, China;,   School of Material Science and Engineering, Taiyuan University of Science and Technology, Taiyuan 030024, China;,   School of Material Science and Engineering, Beifang Nationalities University, Yinchuan 750021, China;,   State Key Laboratory for Advanced Metals and Materials, Beijing University of Science and Technology, Beijing 100083, China
Published: December 2020

The giant magnetoimpedance(GMI) effect of Co-rich microwires makes an opportunity to design sensitive GMI weak magnetic meter sensor. Optimization of magnetic meters needs to improve the GMI response, especially the field sensitivity of microwires. In this study, Co-rich amorphous microwires each with an average diameter of 32 μm are prepared by melt-extracted technique and their GMI characteristics are investigated at frequencies ranging from 0.1 to 10 MHz with and without bias direct voltage applied. Experimental results indicate that the GMI effect of these wires has asymmetric features with the increases of frequency and driving current. It is found that the intrinsic asymmetric GMI (AGMI) response results from the helical anisotropy and magnetization hysteresis of the Co-rich microwires. Furthermore, it is found that there is a pronounced improvement in AGMI response when a bias voltage is applied. In theory, the factor which induces an increase in circular magnetic field causes successive changes in magnetization reversal of the quickly quenched Co-rich microwires with multiple domains and helical anisotropy. As a consequence, the circular magnetization process is enhanced, leading to higher circular permeability and stronger GMI response. Meanwhile, a bias voltage inducing the given circular magnetic field reinforces the magnetization process in a certain direction, which intensifies the asymmetric characteristic of GMI response. For example, the asymmetric ratio between two impedance peaks rises from 1.46% to 12.06% at 1MHz and 3 mA after applying a 1 V bias voltage. Simultaneously, the circular field inclines the magnetization off the axial direction which makes the axially induced magnetization reversal more difficult and occur at a higher switching field. This effect broadens the linear impedance zone; however, it reduces the slope of the impedance with the external field and the field sensitivity increasing to some extent. The balance between these two sides proves that AGMI response is related to the magnetization reversal process which is sensitive to the circular magnetic field. Experimental results indicate that the field sensitivity rises from 616 to 5687 V/T with the impedance linear zone broadening from 0.65 to 1.16 when a 1 V bias voltage is applied, while it decreases to 4525 V/T when the bias voltage futher increases to 2 V at 10 MHz and 5 mA. This reveals that the GMI effect of these amorphous Co-rich microwires with high field sensitivity can be optimized by applying proper bias voltage.
Scintillation properties of Ce3+ doped SiO2-Al2O3-Gd2O3 glass
Authors: Liu Li-Wan  , Zhou Qin-Ling  , Shao Chong-Yun  , Zhang Yu  , Hu Li-Li  , Yang Qiu-Hong  , Chen Dan-Ping  ,   School of Materials Science and Engineering, Shanghai University, Shanghai 200436, China;,   Center of High Power Laser Components, 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

Scintillation glass is an attractive material due to its many advantages including low-cost and easy-manufacturing compared with single crystal. However the low density of glass scintillator restricts its applications. The introduction of heavy components such as PbO and Bi2O3 allows the density of the glass to be easily increased to more than 6.0 g/cm3 which is desirable for most applications. However, it is usually accompanied with a dramatic decrease in the luminescence response of Ce3+ ions. Although Gd2O3 based glass has a relatively high light yield, it is far below the high silica glass. In order to explain why the luminescent efficiency of Ce3+ doped glass with low density is high while that with high density is low, a glass-forming region of SiO2-Al2O3-Gd2O3 ternary system is achieved by high-temperature melt-quenching method. Ce3+doped SiO2-Al2O3-Gd2O3 and SiO2-Al2O3-Gd2O3-Ln2O3 (Ln=Y, La, Lu) scintillation glasses are prepared at reducing atmosphere. Their optical and scintillation properties are investigated. The results show that the content of Gd2O3 can reach as high as 30% mol without phase separation. In addition, the UV cut-off position is red-shifted, PL intensity decreases and decay time reduces from 70 to 37.6 ns with increasing the Gd2O3 concentration. After Lu2O3, La2O3, Y2O3 are added in the glass, the UV cut-off position is red-shifted and PL intensity decreases. Moreover the UV cut-off position is in the order of La>Y>Lu and the decay time is in the order of La2O3 is more than 10% mol, X-ray excited luminescence light emission intensity reduces from 61% of BGO to 13% of BGO. With the UV cut-off position red-shifted, the bandgap of glass becomes narrow, resulting in the 5 d level of Ce3+ ions gradually approaching to the conduction band and the 5 d electrons easily combining with the holes in the glass through the conduction band. Namely, charge transferring quenching occurs. This is the reason why the PL intensity and decay time both decrease. It can also explain why the luminescent efficiency of Ce3+ doped glass with low density is high while that with high density is low.