量子控制的基本概念及其哲学意义

基于量子力学和量子信息的量子控制论正在形成。量子控制显著不同于经典控制。量子控制揭示了新的哲学意义:波函数是量子实在与量子信息的统一,量子状态是可测量性与可控性的统一,量子态是一种重要的资源。     

我国实现国际上最高效的量子态层析测量

我国科学家利用全新量子测量方法,在实验上实现了目前国际上最高效的量子态层析测量.研究成果于4月12日在线发表在国际权威期刊《自然-通讯》上.量子测量是提取量子系统信息必不可少的手段.因此.探索量子测量的能力和局限性对不确定性关系、非局域性等量子物理基本问题研究以及量子计量、量子成像、引力波探测等应用都具有重要意义。     

我国实现16公里自由空间量子态隐形传输

量子态隐形传输是一种全新的通信方式,它传输的不再是经典信息,而是量子态携带的量子信息,它是未来量子通信网络的核心要素。利用量子纠缠技术,需要传输的量子态如同科幻小说中描绘的“超时空穿越”：在一个地方神秘地消失,不需要任何载体的携带,又在另一个地方神秘地瞬间出现。这一奇特现象引起了学术界和公众的广泛兴趣。     

四能级梯模型原子系统中基于部分受激拉曼绝热过程中原子相干的频率上转换研究

近年来,量子干涉效应是现代物理学中的一个重要研究内容,现代光学技术使我们可以精确地通过原子去控制光或通过光去控制原子。比如利用相干制备,我们可以精确地操纵原子系统的光学响应特性,发生一些有趣的物理现象。例如:电磁感应光透明、无反转激光、光速减慢、光与原子纠缠等,这些新的物理效应和相干调控技术产生许多有趣且有应用价值,无论是从计算机科学、物理化学领域,它们都提供了有效研究方法,因此吸引了人们对其产生的浓厚的兴趣。通过科学家们不断努力研究发现在量子态操控中,如何保持量子态相干是最大的困难。而光和原子相互作用产生的相干和干涉现象将为量子态相干操控提供很好的思路和方法。通过科学家们不断努力研究发现在量子态操控中,如何保持量子态相干是最大的困难。而光和原子相互作用产生的相干和干涉现象将为量子态相干操控提供很好的思路和方法。     

量子纠缠态制备、操纵的实验研究

量子纠缠是量子信息学中最重要也是最为奇特的一个课题.在量子信息学中,量子信息的处理离不开量子态及其操纵,而量子纠缠态毫无疑问是各种各样的量子态中最重要的一种. 利用光子纠缠态开展了以下实验研究:(1)利用连续波激光束泵浦非线性晶体的自发参量下转换过程,制备出了双光子偏振纠缠态,具有较高亮度和纠缠度,并具有纠缠度可调谐的特点. 利用这种纠缠源,制备了量子信息学中一种重要的混合态——Werner态,采用的方案使得Werner态中纠缠的成分是可控制的.(2)利用线性光学元件以及路径比特概念的引入,在实验上用单光子实现了Buek-Hillery普适克隆机,实验结果表明,对任意的输入纯态,此克隆机输出的2份拷贝与初始态均达到5/6的保真度,与理论计算一致.(3)在实验上利用自发参量下转换系统制备的双光子偏振最大纠缠态及非最大纠缠态进行了CHSH不等式的检验,验证了对于2比特纠缠纯态,"纠缠"等价于"Bell不等式违背"这一结论.(4)除了局域隐变量理论之外,还有一种主要的隐变量理论——环境无关的隐变量理论(NCHV),关于这种隐变量,类似于Bell不等式,有一个Kochen-Specker理论,其主要内容是证明NCHV和量子力学的矛盾. 完成了一个用单光子实现的检验Kochen-Spcker理论的实验,实验结果证明了NCHV是不存在的.     

量子隐形传输中的幺正操作

量子隐形传输是量子通信主要的研究内容,通过研究基于GHZ态的两体Bell态量子隐形传输来研究不同量子态测量结果所对应幺正操作的变化。     

双态体系中的量子态超空间转移

文章从量子力学出发，简要介绍了其理论的发展历程，分析了EPR理论中非定域特性的内在特性，并由此而引出量子态的超空间转移（量子通信），重点阐述了双态体系中量子态超空间转移的实现，并简要说明了目前量子通信方面的研究成果。     

神秘隧道能让物质瞬间转移

量子就是物质粒子的非连续运动。量子态是指原子、中子、质子等粒子的状态,它可表征粒子的能量、旋转、运动、磁场以及其他的物理特性。1993年,美国物理学家贝尼特等人提出了“量子态隐形传输”的方案:将原粒子物理特性的信息发向远处的另一个粒子,该粒子在接收到这些信息后,会成为原粒子的复制品。而在此过程中,传输的是原粒子的量子态,而不是原粒子本身。传输结束后,原粒子已经不具备原来的量子态,而有了新的量子态。星球战士从某一地点突然消失,而瞬间出现在遥远的另一点。《封神演义》中的土行孙,会突然消失,一转眼又从别的地方冒出来……     

威力超群的量子武器

正我国首颗量子科学实验卫星将于2016年8月择机发射,这是世界上首次实现卫星和地面之间的量子通信。因其运用量子物理基本原理,具有单光子的不可分割性和量子态的不可复制性,确保了信息的不可窃听和不可破解,从原理上确保身份认证、传输加密以及数字签名等的无条件安全,可以有效解决信息安全问题。所谓量子理论,从微观领域来讲,就是某些物质可同时处于多个可能状态的叠加态,只     

信息技术

正大规模硅基集成高维光量子芯片实现北京大学"极端光学创新研究团队"王剑威、龚旗煌教授等与布里斯托尔大学物理系量子光学中心等单位合作,利用大规模集成硅基纳米光量子芯片技术,实现对高维度光量子纠缠体系的高精度和普适化量子调控和量子测量,研究论文发表于Science。实现功能强大的量子信息处理芯片是当前量子科技革命的关键。研究团队实现了一种新型的多路径加载高维量子态方式,即每个光子以量子叠加态的形式同时存在于多条光波导路径,从而实现了一个高达15×15的高维量子纠缠系统。通过可控地激发16个参量四波混频单光子源阵列,可以制备具有任意复系数的高维度量子纠缠态。     

Optimal linear attack for multi-sensor network against state estimation

This paper is concerned with a security problem about malicious integrity attacks in state estimation system, in which multiple smart sensors locally measure information and transmit it to a remote fusion estimator though wireless channels. A joint constraint is considered for the attacker behaviour in each channel to keep stealthiness under a residual-based detector on the remote side. In order to degrade the estimator performance, the attacker will maximize the trace of the remote state estimation error covariance which is derived based on Kalman filter theory. It is proved that the optimal linear attack strategy design problem is convex and finally turned into a semi-definite programming problem. In addition, the tendency of attack behaviour on recursive and fixed Kalman filter system is analyzed. Several examples are given to illustrate the theoretical results.     

On the dynamics of a quantum coherent feedback network of cavity-mediated double quantum dot qubits

The purpose of this paper is to present a comprehensive study of a coherent feedback network where the main component consists of two distant double quantum dot (DQD) qubits which are directly coupled to a cavity. This main component has recently been physically realized (van Woerkom et al., Microwave photon-mediated interactions between semiconductor qubits, Physical Review X, 8(4):041018, 2018). The feedback loop is closed by cascading this main component with a beamsplitter. The dynamics of this coherent feedback network is studied from three perspectives. First, an analytic form of the output single-photon state of the network driven by a single-photon state is derived. In contrast to the experimental observations made in the above paper where a laser is used as input, new interesting physical phenomena are revealed by means of single-photon input. Second, excitation probabilities of DQD qubits are computed when the network is driven by a single-photon input state. Finally, if the input is vacuum but one of the two DQD qubits is initialized in its excited state, the explicit expression of the steady-state joint system-field state is derived, which shows that the output single-photon field and the two DQD qubits can form an entangled state if the transition frequencies of two DQD qubits are equal. This analytical expression can be used to interpret experimental results in the existing literature.     

Orbit consensus of quantum networks based on interaction design

For a general quantum network system with a non-zero Hamiltonian H composed of n identical m-level quantum subsystems, any symmetric consensus state in the interaction picture exactly corresponds to an orbit in the Schrödinger picture, which is called the H-orbit of the symmetric consensus state. By using the interaction picture transformation and the tool of the LaSalle invariance principle, this paper analyzes the orbit consensus of this quantum network and designs the corresponding swapping operators such that the system converges to the H-orbit of the target symmetric consensus state that exists in the interaction picture. In particular, we prove the convergence of the quantum network to the H-orbit when the quantum interaction graph is connected and the system Hamiltonian is permutation invariant. The orbit consensuses of a four-qubit network system and a quantum network of three identical three-level subsystems are achieved numerically, which verifies the correctness of our theoretical results and the effectiveness of the designed swapping operators.     

旋转接头的选型、安装及维护

介绍了旋转接头的选型,安装前的准备工作和注意事项,以及旋转接头的安装顺序,并对旋转接头安装使用后就开始产生泄漏的原因和处置对策进行分析。     

Optimal DoS attack scheduling for multi-sensor remote state estimation over interference channels

In this paper, we investigate the optimal denial-of-service attack scheduling problems in a multi-sensor case over interference channels. Multiple attackers aim to degrade the performance of remote state estimation under attackers’ energy constraints. The attack decision of one attacker may be affected by the others while all attackers find their own optimal strategies to degrade estimation performance. Consequently, the Markov decision process and Markov cooperative game in two different information scenarios are formulated to study the optimal attack strategies for multiple attackers. Because of the complex computations of the high-dimensional Markov decision process (Markov cooperative game) as well as the limited information for attackers, we propose a value iteration adaptive dynamic programming method to approximate the optimal solution. Moreover, the structural properties of the optimal solution are analyzed. In the Markov cooperative game, the optimal joint attack strategy which admits a Nash equilibrium is studied. Several numerical simulations are provided to illustrate the feasibility and effectiveness of the main results.     

GSM／GPRS在全球定位监控报警系统中的应用研究

本文提出一种在全球性定位监控报警系统采用GPRS无线通信技术进行信息的传输,系统可通过发送短信方式,对各个功能模块的状态进行远程监控,异常情况时可远程操作该系统,实现智能化全球监控。     

哲学与物理学相遇在量子世界

文章通过分析量子力学中量子态的本体论地位问题、量子场论中何谓基本粒子问题,以及量子引力理论中时间是否存在的问题,表明科学理论的内核是一些基本的形而上学预设。文章指出,哲学与物理学的关系,颇类似于数学与物理学的关系,因此在物理学和哲学之间建立更紧密的联盟,会有助于这些问题的澄清与解决。     

Observer-based feedback control of two-level open stochastic quantum system

The observer-based feedback control for the two-level bilinear open stochastic quantum system is proposed in this paper. The state of open stochastic quantum system (OSQS) is described in the Cartesian coordinate system. The proposed state observer is designed by using state-dependent differential Riccati equation (SDDRE) and constructed for optimally estimating the state of OSQS from measurement output of the system. The state of observer is continuously updated by the output data of continuous weak measurement (CWM). A Lyapunov Feedback control is designed based on estimated state of the observer for the state transfer of OSQS. An exponential Lyapunov function is chosen to ensure the stability of the system. The observer-based Lyapunov feedback control (OLFC) strategy is developed according to the stochastic Lyapunov stability theorem. The numerical simulation results verify the achievability of the proposed OLFC strategy in terms of state estimation and state transfer of OSQS. Numerical simulations demonstrate that the observer tracks the state of system asymptotically with minimum error of ± 3%. The proposed OLFC has the ability to move the state of OSQS from arbitrary initial state to the final target eigenstate with high fidelity ≥ 90%.     

Quantum coding demonstrated feasible to overcome qubit loss error

Inspired by quantum mechanics, people have been dreaming of a new type of computers to revolutionize computing technique - quantum computers. Such dream machines take advantage of the fact that the quantum bit （qubit）, the fundamental unit of quantum information, can be in a superposition state and thus is able to store massive data and solve complicated problems at an incredible speed beyond the capacity of classical computers.     

Stabilizing a class of mixed states for stochastic quantum systems via switching control

The global stabilization of a class of mixed states for finite dimensional stochastic quantum systems with degenerate measurement operator is investigated in this paper. We construct a measurement operator and control Hamiltonian that make the target state one of the system equilibria. Based on the proposed Lyapunov function, a control law is designed following Lyapunov’s method to steer system state to the target mixed state from an initial state in the convergence domain, which is obtained through the analyses of invariant set based on LaSella’s invariance principle. When the initial state isn’t in the convergence domain, a constant control is used to steer the system state so that it enters the convergence domain in finite time. The constant control and the control designed by Lyapunov method compose a switching control strategy, which can steer system state to the target mixed state from any arbitrary state in the state space, i.e., the target mixed state is globally stable under the switching control. The convergence of the switching control is proved based on state sample trajectories. Moreover, the numerical experiments on a three dimensional stochastic quantum system are performed to demonstrate the effectiveness of switching control.