理想条件下混合态量子系统的Lyapunov稳定化策略

在假定被控系统满足非退化、没有退化跃迁和完全连通的理想条件下,借助于带有附加自由度的Lyapunov函数研究了混合态量子系统的稳定化问题.基于LaSalle原理推导了闭环系统的最大不变集和任一初始态下的收敛状态集,给出了系统对最大不变集中任一平衡态渐近稳定化的自由度的构造原则.最后通过一个两能级系统的数值仿真,验证了所得理论结果的正确性.     

Diffserv中基于测量的准入控制

针对当前Internet只能提供传统的尽力而为(Best Effort)服务，不能提供QoS(Quality of Service）的问题，IETF（Internet Engineering Task Force,Internet任务工程组)提出了几种解决方案，包括Intserv,Diffserv和MPLS。主要介绍了其中的Diffserv体系结构，并介绍在Diffserv中加入准入控制的几种方式。     

Noisy metrology: a saturable lower bound on quantum Fisher information

Quantum Information Processing - We present a general problem of quantum entanglement quantified by von Neumann entropy for N-level atomic system. Time evolution of state vector of the entire...     

Quantum correlation via quantum coherence

Quantum correlation includes quantum entanglement and quantum discord. Both entanglement and discord have a common necessary condition—quantum coherence or quantum superposition. In this paper, we attempt to give an alternative understanding of how quantum correlation is related to quantum coherence. We divide the coherence of a quantum state into several classes and find the complete coincidence between geometric (symmetric and asymmetric) quantum discords and some particular classes of quantum coherence. We propose a revised measure for total coherence and find that this measure can lead to a symmetric version of geometric quantum correlation, which is analytic for two qubits. In particular, this measure can also arrive at a monogamy equality on the distribution of quantum coherence. Finally, we also quantify a remaining type of quantum coherence and find that for two qubits, it is directly connected with quantum nonlocality.     

Measurement-based modification of NURBS surfaces

A frequent requirement in computer aided design and manufacture is to update or refine an existing CAD model using measured data. Least squares surface fitting is known to suffer from stability problems, caused by an insufficient measurement density in some regions. This is particularly evident in situations involving local surface updating and when knot insertion is applied for local surface refinement. This paper presents a new method to update the CAD model consisting of NURBS surfaces, trimmed or untrimmed, based on a set of unorganised measured points in three-dimensional space. The proposed method overcomes the fundamental problem of singular or ill-conditioned matrices resulting from incomplete data sets. This was achieved by introducing additional fitting criteria in the minimisation functional, which constrain the fitted surface in the regions with insufficient number of data points. Two main benefits were realised by this approach. First, local surface updating can be performed by treating the surface as a whole, without the need to specially identify the regions with insufficient data, nor to re-measure those regions. Second, the quality of the unmeasured regions may be controlled to suit specific needs. The results were found to be highly encouraging and the method was found to be especially useful in situations involving knot insertion and large surface deformations.     

一种基于延时PDF测量的连接接纳控制算法

相比与基于模型的连接接纳控制(CAC)算法,基于测量的CAC (MBCAC)算法能够大大提高了网络资源的利用率.准确的网络状态信息时于提高MBCAC的性能至关重要.本文提出了一种基于延时概率密度函数测量的CAC算法,它采用了两种机制有效提高了网络状态测量的准确性.一是测量网络中每个路由器出口的延时概率密度函数,二是通过混合更新方法及时更新网络状态.仿真结果表明它在保证业务服务质量要求的前提下能有效提高网络状态测量的准确性,具有较低的业务流拒绝率和较高的链路利用率.     

一种基于延时PDF测量的连接接纳控制算法

相比与基于模型的连接接纳控制(CAC)算法,基于测量的CAC(MBCAC)算法能够大大提高了网络资源的利用率。准确的网络状态信息对于提高MBCAC的性能至关重要。本文提出了一种基于延时概率密度函数测量的CAC算法,它采用了两种机制有效提高了网络状态测量的准确性。一是测量网络中每个路由器出口的延时概率密度函数,二是通过混合更新方法及时更新网络状态。仿真结果表明它在保证业务服务质量要求的前提下能有效提高网络状态测量的准确性,具有较低的业务流拒绝率和较高的链路利用率。     

Measurement-based modelling of Internet dial-up access connections

The traffic generated by dial-up access to the Internet is a major cause of overload on the telephone network, spurring the need for call level traffic characterization. The results of a measurement campaign on calls directed to Internet Service Providers are here used to analyze models for their arrival process and for their holding time. The arrival process can be described by a Poisson model but with a variable mean frequency of arrivals within the hour. The hyperexponential model is selected for the probability density function of the call holding times, with mean value of about 15 min most of the day.     

基于时空相似度量的复杂场景背景估计

针对复杂场景中背景的不完整性、背景噪声的影响以及场景中目标运动快慢不一等影响背景估计的因素,该文提出了一种基于时空相似度量的估计视觉监视场景背景的递进式策略。首先利用无运动假设分析时域相似度量矩阵中相邻时刻有运动的子块对,将相似度量矩阵分解为连续的相对平坦子相似矩阵;然后在子相似矩阵中,搜索候选背景子块集合,通过度量与邻近时刻的时域相似度及子块周围场景的空间相似度,判别最可能的背景子块;最后对于一直有运动目标遮挡的位置直接进行有损重建。该方法对噪声、运动目标速度有较强的适应性,计算代价较低。     

Quantum Fisher information,quantum entanglement and correlation close to quantum critical phenomena

In this paper, we investigate the quantum Fisher information (QFI), quantum entanglement, quantum correlation and quantum phase transition (QPT) within the one-dimensional transverse Ising model by exploiting quantum renormalization-group method. The results show that quantum Fisher information, quantum entanglement, quantum correlation can evolve to two saturated values which exhibit QPT at the critical point after several iterations of the renormalization. Meanwhile, we find quantum entanglement or correlation can be detected perfectly by means of quantum Fisher information. Besides, it cannot capture any information about the system in the paramagnetic phase in view of quantum entanglement and correlation. Contrarily, it is evident the QFI is always nonzero even if the system is in the paramagnetic phase, i.e., the QFI can also be utilized as a highly favorable measure of quantum information in a broad of quantum spin systems. Furthermore, we disclose the nonanalytic and scaling behaviors of quantum Fisher information, which can be taken as a representation of quantum critical characterism.     

基于混合量测的动态状态估计算法研究

基于SCADA/PMU混合量测的电力系统动态状态估计算法,目前主要是先进行量测变换再进行动态估计,尝试结合静态估计和动态估计的优点,提出一种新的方法.该方法首先对SCADA量测数据运用经典的加权最小二乘法(WLS)进行静态状态估计,估计结果和PMU量测中的电压相量共同形成量测数据集,再进行线性动态状态估计.WLS方法能保证状态估计的质量和算法的收敛性能,同时线性动态估计只选用PMU量测的电压相量,避免量测变换及其产生的误差,而且雅可比矩阵高度稀疏,计算时间较短.在IEEE14节点系统上的仿真结果表明,此方法具有较好的滤波和预测效果.     

Scattering-induced quantum correlation in electronic waveguides with static magnetic impurities

Entanglement generation due to low-energy scattering of the transporting electrons in an electronic waveguide by a quantum dot magnetic impurity is theoretically investigated. The transverse confining potential of the waveguide is considered as a two-dimensional harmonic potential, and the interaction of the electron with the impurity is described by a zero-range pseudopotential modulated by an Ising or a Heisenberg spin interaction. Our calculation shows that the scattering process leads to creation of a considerable amount of entanglement in the state of the reflected and transmitted electrons. The situation is extended to the scattering of the electrons by two well-separated magnetic impurities localized on the nanowire axis. It is shown that the scattering process causes the magnetic impurities embedded in the nanowire to share their quantum information; subsequently, they can be entangled by spin interaction with the injected electron. The created entanglement between the impurities is calculated and discussed. It is shown that the exact three-dimensional problem can be approximated as a one-dimensional problem under certain circumstances. The approximate results are compared to exact calculations and discussed.     

Measurement-based characterization and classification of QoS-enhanced systems

Quality-of-service mechanisms and differentiated service classes are increasingly available in networks and Web servers. While network and Web server clients can assess their service by measuring basic performance parameters such as packet loss and delay, such measurements do not expose the system's core QoS functionality such as multiclass service discipline. In this paper, we develop a framework and methodology for enabling network and Web server clients to assess system's multiclass mechanisms and parameters. Using hypothesis testing, maximum likelihood estimation, and empirical arrival and service rates measured across multiple time scales, we devise techniques for clients to: 1) determine the most likely service discipline among earliest deadline first, class-based weighted fair queuing, and strict priority; 2) estimate the system's parameters with high confidence; and (3) detect and parameterize non work-conserving elements such as rate limiters. We describe the important role of time scales in such a framework and identify the conditions necessary for obtaining accurate and high confidence inferences.     

一种基于度量的Web服务质量机制

提出了一种简单、准确和高效的带宽调节算法,该算法对每一个服务请求设置一个带宽标准,同时根据对服务请求的分类和Web服务器系统的有效带宽,来分配及调节每一个服务请求的实际带宽,构成一种基于度量的Web服务质量机制,使Web服务器系统能为不同类型的客户请求提供有区分的和有服务质量的Web服务。     

Fuzzy optical metrology

When operating in the real world, the conventional fuzzy approach is to extract crisp data then fuzzify it. This paper explores the concept of measuring fuzzy set memberships directly and obtaining the underlying crisp values by defuzzification. Both speed and accuracy advantages of fuzzy over conventional, crisp metrology are noted     

Protecting quantum entanglement and correlation by local filtering operations

In this work, the protection of different quantum entanglement and correlation is explored by local filtering operations. The results show that the filtering operations can indeed be useful for combating amplitude-damping decoherence and recovering the quantum entanglement and correlation. In this scheme, although the final states satisfy the quantum entanglement and correlation, the corresponding initial noisy states does not satisfy them, which means that the filtering operations can reveal the hidden genuine quantum entanglement and correlation of these initial noisy states.     

Study of quantum correlation swapping with relative entropy methods

To generate long-distance shared quantum correlations (QCs) for information processing in future quantum networks, recently we proposed the concept of QC repeater and its kernel technique named QC swapping. Besides, we extensively studied the QC swapping between two simple QC resources (i.e., a pair of Werner states) with four different methods to quantify QCs (Xie et al. in Quantum Inf Process 14:653–679, 2015). In this paper, we continue to treat the same issue by employing other three different methods associated with relative entropies, i.e., the MPSVW method (Modi et al. in Phys Rev Lett 104:080501, 2010), the Zhang method (arXiv:1011.4333 [quant-ph]) and the RS method (Rulli and Sarandy in Phys Rev A 84:042109, 2011). We first derive analytic expressions of all QCs which occur during the swapping process and then reveal their properties about monotonicity and threshold. Importantly, we find that a long-distance shared QC can be generated from two short-distance ones via QC swapping indeed. In addition, we simply compare our present results with our previous ones.     

Revealing quantum correlation by negativity of the Wigner function

We analyze two two-mode continuous variable separable states with the same marginal states. We adopt the definition of classicality in the form of well-defined positive Wigner function describing the state and find that although the states possess positive local Wigner functions, they exhibit negative Wigner functions for the global states. Using the negativity of Wigner function as an indicator of nonclassicality, we show that despite these states possess different negativities of the Wigner function, they do not reveal this difference as phase space nonclassicalities such as negativity of the Mandel Q parameter or quadrature squeezing. We then concentrate on quantum correlation of these states and show that quantum discord and local quantum uncertainty, as two well-defined measures of quantum correlation, manifest the difference between negativity of the Wigner functions. The non-Gaussianity of these states is also examined and show that the difference in behavior of their non-Gaussianity is the same as the difference between negativity of their Wigner functions. We also investigate the influence of correlation rank criterion and find that when the states can be produced locally from classical states, the Wigner functions cannot reveal their quantum correlations.