Hong–Ou–Mandel interference with two independent weak coherent states

Recently, the Hong-Ou-Mandel （HOM） interference between two independent weak coherent pulses （WCPs） has been paid much attention due to the measurement-device-independent （MDI） quantum key distribution （QKD）. Using classical wave theory, articles reported before show that the visibility of this kind of HOM-type interference is 〈 50%. In this work, we analyze this kind of interference using quantum optics, which reveals more details compared to the wave theory. Analyses confirm the maximum visibility of 50%. And we conclude that the maximum visibility of 50% comes from the two single-photon states in WCPs, without considering the noise. In the experiment, we successfully approach the visibility of 50% by using WCPs splitting from the single pico-second laser source and phase scanning. Since this kind of HOM interference is immune to slow phase fluctuations, both the realized and proposed experiment designs can provide stable ways of high-resolution optical distance detection.

Decoherence suppression for three-qubit W-like state using weak measurement and iteration method

Multi-qubit entanglement states are the key resources for various multipartite quantum communication tasks. For a class of generalized three-qubit quantum entanglement, W-like state, we demonstrate that the weak measurement and the reversal measurement are capable of suppressing the amplitude damping decoherence by reducing the initial damping factor into a smaller equivalent damping factor. Furthermore, we propose an iteration method in the weak measurement and the reversal measurement to enhance the success probability of the total measurements. Finally, we discuss how the number of the iterations influences the overall effect of decoherence suppression, and find that the ＂half iteration＂ method is a better option that has more practical value.

Passive decoy-state quantum key distribution for the weak coherent photon source with finite-length key

Passive decoy-state quantum key distribution systems, proven to be more desirable than active ones in some scenarios, also have the problem of device imperfections like finite-length keys. In this paper, based on the WCP source which can be used for the passive decoy-state method, we obtain the expressions of single-photon error rates, single-photon counts, and phase error rates. According to the information of smooth min-entropy, we calculate the key generation rate under the condition of finite-length key. Key generation rates with different numbers of pulses are compared by numerical simulations. From the results, it can be seen that the passive decoy-state method can have good results if the total number of pulses reaches 1010. We also simulate the passive decoy-state method with different probabilities of choosing a pulse for parameter estimation when the number of pulses is fixed.

Constraining Equation of State of Dark Matter:Including Weak Gravitational Lensing

Usually the equation of state （EoS） of dark matter is zero when it is cold, however there exists the possibility of a （effective） nonzero EoS of dark matter due to its decay and interaction with dark energy. In this work, we try to constrain the EoS of dark matter/JAdm using the currently available cosmic observations which include the geometrical and dynamical measurements. For the geometrical measurements, the luminosity distance of type Ia supernovae, the angular diameter distance and comoving sound horizon from baryon acoustic oscillations and the cosmic microwave background radiation will be employed. The data points from the redshift-space distortion and weak gravitational lensing will be taken as dynamical measurements. Using the Markov chain Monte Carlomethod, we obtain a very tight constraint on the-EoS of dark matter：wdm=0.0000532 ＋0.000692＋0.00136＋0.00183 -0.000686-0.00136-0.00177.

Weak wide-band signal detection method based on small-scale periodic state of Duffing oscillator

The conventional Duffing oscillator weak signal detection method, which is based on a strong reference signal, has inherent deficiencies. To address these issues, the characteristics of the Duffing oscillator＇s phase trajectory in a small- scale periodic state are analyzed by introducing the theory of stopping oscillation system. Based on this approach, a novel Duffing oscillator weak wide-band signal detection method is proposed. In this novel method, the reference signal is discarded, and the to-be-detected signal is directly used as a driving force. By calculating the cosine function of a phase space angle, a single Duffing oscillator can be used for weak wide-band signal detection instead of an array of uncoupled Duffing oscillators. Simulation results indicate that, compared with the conventional Duffing oscillator detection method, this approach performs better in frequency detection intervals, and reduces the signal-to-noise ratio detection threshold, while improving the real-time performance of the system.

Passive decoy-state quantum key distribution using weak coherent pulses with modulator attenuation

Passive decoy-state quantum key distribution is more desirable than the active one in some scenarios. It is also affected by the imperfections of the devices. In this paper, the influence of modulator attenuation on the passive decoy-state method is considered. We introduce and analyze the unbalanced Mach-Zehnder interferometer, briefly, and combining with the virtual source and imaginary unitary transformation, we characterize the passive decoy-state method using a weak coherent photon source with modulator attenuation. According to the attenuation parameter 6, the pass efficiencies are given. Then, the key generation rate can be acquired. From numerical simulations, it can be seen that modulator attenuation has a non- negligible influence on the performance of passive-state QKD protocol. Based on the research, the analysis method of virtual source and imaginary unitary transformation are preferred in analyzing passive decoy state protocol, and the passive decoy-state method is better than the active one and is close to the active vacuum ＋ weak decoy state under the condition of having the same modulator attenuation.

Implementation of nonlocal Bell-state measurement and quantum information transfer with weak Kerr nonlinearity

We propose a protocol to implement the nonlocal Bell-state measurement, which is nearly determinate with the help of weak cross-Kerr nonlinearities and quantum non-destructive photon number resolving detection. Based on the nonlocal Bell-state measurement, we implement the quantum information transfer from one place to another. The process is different from conventional teleportation but can be regarded as a novel form of teleportation without entangled channel and classic communication.

WEAK FORMULATION OF MIXED STATE EQUATION ANDBOUNDARY VALUE PROBLEM OF LAMINATEDCYLINDRICAL SHELL

Weak formulation of mixed state equations including boundary conditions are presented in a cylindrical coordinate system by introducing Hellinger-Reissner variational principle. Analytical solutions are obtained for laminated cylindrical shell by means of state space method. The present study extends and unifies the solution of laminated shells.

基于多光子叠加态的交叉相位调制耦合参数测量

继纠缠之后,粒子间相互作用已成为量子增强的重要资源.在不利用纠缠资源的前提下,已有研究工作利用单光子叠加态与相干态的相互作用实现了精度为海森堡极限的参数测量,然而海森堡极限并不是这个相互作用模型的测量精度极限.为了得到更高的测量精度,将单光子叠加态替换为多光子叠加态,在弱测量框架下对信号光量子态进行后选择与量子态筛选.将单光子叠加态替换为多光子叠加态,能为测量结果带来全方位提升.提出基于多光子叠加态的交叉相位调制耦合参数测量的物理方案,该物理方案具有搭建难度低及操作简单的优点.

强国家的体制形象与社会镜像——重思国家能力形象的二重性

国家能力形象的二重性涉及国家能力的体制形象与社会镜像之间的关系。基层行政主体的行为策略决定了体制性国家与基层社会的关系状态,基层社会基础决定了基层行政主体对体制性强国家的适应模式。在统合化社会,基层行政主体对体制性强国家的反噬式适应形塑了社会镜像中的弱国家形象;在寡头化社会,基层行政主体对体制性强国家的亢奋式适应形塑了社会镜像中的超强国家形象;在派性化社会,基层行政主体对体制性强国家的协商式适应形塑了社会镜像中的次强国家形象。经验表明,决定一个国家在政治实践中是强国家还是弱国家的关键并不必然在于基层社会反抗力量的强弱,也有可能在于基层行政主体对体制性强国家的适应方式。高度一统性的体制性强国家在基层治理层面表现为超强国家、次强国家和弱国家的复杂“拼图”。

基于弱稳态检测的燃煤锅炉热值校正方法

燃料热值自适应控制是提升协调控制系统控制品质的关键技术之一。现有的热值校正技术仍主要采用英制热量单位(BTU)校正器,难以实现燃料热值精准、快速校正。提出了一种基于弱稳态检测的燃料热值校正新方法。首先,实时检测机组运行参数,动态构建弱稳态邻近模型。其次,设计热值校正控制回路,将模型输出用于协调控制系统中,解决燃料热值在线动态校正的行业难题。应用结果表明:基于弱稳态检测的热值校正方法,能够准确地计算当前煤质下的燃料热值校正量,缩短协调控制系统闭环调节过程,降低机组负荷、主蒸汽压力、中间点温度的控制偏差,全面提升机组协调控制品质。该方法具有较高的校正精度,实现模型动态更新,能够较快地掌握机组热值变化情况,可用于开展配煤掺烧的火力发电机组。

基于弱配位环境的晶态锌离子固态电解质

二次锌电池是一类低成本、环保和高安全的规模储能技术,但是一直以来锌金属负极与传统水系电解液兼容性不足以及严重的枝晶生长问题限制了电池能量密度和寿命。发展固态二次锌电池是根本解决上述瓶颈问题的有效路线之一,但是,二价锌离子电荷密度高,其在无机陶瓷电解质和聚合物电解质中的室温固相传导极为困难。本工作以具有层状晶体结构的三氟甲基磺酸锌[Zn(TFO)_(2)]作为离子盐主体骨架,通过引入“软碱”的双齿弱配位配体——丁二腈(SN)重塑锌离子的固相配位环境,发展了一类晶态配位化合物的锌离子固态电解质[Zn(TFO)_(2)(SN)_(n)]。得益于氰基官能团(—CN)与三氟甲基磺酸阴离子(TFO^(-))的共配位结构,阴离子骨架对锌离子的静电束缚得到了显著降低,锌离子室温固态离子电导率实现了3个数量级的提升[由Zn(TFO)_(2)的1.1×10^(-9)S/cm提升至1.8×10^(-6)S/cm]。基于该类固态电解质,Zn||Zn对称电池可实现低极化电压(0.08 V,0.05 mA/cm^(2))的长周期锌沉积/溶解循环,并且实现了全固态锌空气电池在室温下的可逆充放电。

高比例新能源电力系统可靠性高效评估和薄弱环节辨识方法

新能源渗透率的提高可能诱发供电中断的风险,使电力系统的运行可靠性降低,传统的中长期可靠性评估方法难以满足运行可靠性评估的时间需求。本文提出了一种电力系统运行可靠性高效评估算法,揭示了电力系统运行可靠性指标与风电出力不确定性因素的解析函数关系,避免不确定性因素变化时可靠性的重复计算。首先,基于隐马尔可夫模型对风电出力的分布特性进行建模;然后,通过状态枚举-混沌多项式展开方法建立可靠性指标与风电出力间的解析函数;最后,基于解析函数实现对实时风电出力下的新能源电力系统运行可靠性的高效评估及薄弱环节辨识。以修改的IEEE-RTS79系统为例进行分析计算,验证了所提方法的有效性。

基于四电平编码与弱光通信的极低功耗传光式电流互感器

针对传光式电流互感器高压侧现有的母线取能和激光供能方式存在供电死区、能量转换效率低、使用寿命不足等问题,提出一种基于四电平编码与弱光通信的极低功耗光电传输系统方案。首先,设计三态门电路将信号采集模块的采样时钟和数据信号叠加为一个四电平信号。然后,利用超高亮度且极低功耗的LED将四电平信号转换为光信号并通过光纤传输至低压侧。最后,在低压侧通过高灵敏度雪崩光电二极管探测器进行弱光检测后输入解码电路实现信号解码。将极低功耗光电传输系统应用于传光式电流互感器中进行实验验证,测量结果满足0.2级精度要求,系统高压侧的平均功耗可降低至3.91 mW,保证测量精度的同时大幅降低了功耗。由于高压侧的功耗极低,故可采用大容量电池或小功率光伏系统等可靠供能方案,从而解决了高压侧的供能问题,提高了系统的稳定性和可靠性。

Generation of entanglement molecules via weak coherent field in cavity QED

This paper presents a method for generating entanglement molecules, which is introduced by Dur （2001 Phys. Rev. A）. In this scheme, N ladder-type three-level atoms are sent through a resonant weak coherent cavity field, then the system states are measured. And the system field may collapse onto some possible types of entanglement molecules. Meanwhile it discusses about the interaction time from the experimental point of view, and compare the result with the previous scheme proposed by Huang （2004 J. Phys. B： At. Mol. Opt. Phys.）.

Impurity effect on surface states of Bi(111) ultrathin films

The surface impurity effect on the surface-state conductivity and weak antilocalization（WAL） effect has been investigated in epitaxial Bi（111） films by magnetotransport measurements at low temperatures. The surface-state conductivity is significantly reduced by the surface impurities of Cu, Fe, and Co. The magnetotransport data demonstrate that the observed WAL is robust against deposition of nonmagnetic impurities, but it is quenched by the deposition of magnetic impurities which break the time reversal symmetry. Our results help to shed light on the effect of surface impurities on the electron and spin transport properties of a 2D surface electron systems.

Analysis of a kind of Duffing oscillator system used to detect weak signals

The stability of the periodic solution of the Duffing oscillator system in the periodic phase state is proved by using the Yoshizaw theorem, which establishes a theoretical basis for using this kind of chaotic oscillator system to detect weak signals. The restoring force term of the system affects the weak-signal detection ability of the system directly, the quantitative relationship between the coefficients of the linear and nonlinear items of the restoring force of the Duffing oscillator system and the SNR in the detection of weak signals is obtained through a large number of simulation experiments, then a new restoring force function with better detection results is established.

Vector tracking loops in GNSS receivers for dynamic weak signals

Vehicle positioning with the global navigation satellite system （GNSS） in urban environments faces two problems which are attenuation and dynamic. For traditional GNSS receivers hardly able to track dynamic weak signals, the coupling between all visible satellite signals is ignored in the absence of navigation state feedback, and thermal noise error and dynamic stress threshold are contradictory due to non-coherent discriminators. The vector delay/frequency locked loop （VDFLL） with navigation state feedback and the joint vector tracking loop （JVTL） with coherent discriminator which is a synchronization parameter tracking loop based on maximum likelihood estimation （MLE） are proposed to improve the tracking sensitivity of GNSS receiver in dynamic weak signal environments. A joint vector position tracking loop （JVPTL） directly tracking user position and velocity is proposed to further improve tracking sensitivity. The coherent navigation parameter discriminator of JVPTL, being able to ease the contradiction between thermal noise error and dynamic stress threshold, is based on MLE according to the navigation parameter based linear model of received baseband signals. Simulation results show that JVPTL, which combines the advantages of both VDFLL and JVTL, performs better than both VDFLL and JVTL in dynamic weak signal environments.

强国家的经济与社会根源:《强社会与弱国家》的视角

强国家常常被认为与国家内部的制度化和理性化息息相关,也常被认为是政治精英至上而下的国家建设努力的结果。但是,强国家还有深刻的社会结合和经济根源。对于社会和经济如何影响到强大国家,不同研究给出了不同的回答。不同于许多研究强调经济发展推动政治发展与强社会造就强国家的观点,米格代尔的研究关注第三世界国家社会和经济对于国家能力更复杂的影响,揭示了与国家争夺社会控制的社会力量以及全球扩散的资本主义体系对于第三世界国家现代国家建设的影响。这些研究对我们理解中国国家能力的成长具有重要的启示意义。

弱电网下基于谐波状态空间模型的光储—虚拟同步发电机稳定性分析与优化控制研究

虚拟同步发电机(virtual synchronous generator,VSG)技术因提供阻尼和惯量而被广泛用于新能源并网逆变器。光储并入弱电网易发生频率耦合等问题,因而VSG并网稳定性分析变得更加复杂。针对光储并入弱电网系统,考虑频率耦合,在dq域中建立基于谐波状态空间(harmonic state space,HSS)理论的多时间尺度虚拟同步发电机模型。采用归一化参数灵敏度分析法,揭示功率环、电压环和低通滤波中虚拟惯量J、虚拟阻尼D_(p)、下垂系数K_(u)、比例系数k_(pu)和截止频率ω_(c)等关键控制参数根轨迹的特性和电网强度对系统稳定性的影响。并通过调整优化控制参数,提高系统稳定性。最后在Matlab/Simulink仿真平台验证谐波状态空间模型精确度和关键参数根轨迹特性。