Control Protocol of Finite Dimensional Quantum Systems

An analytic control protocol of two types of finite dimensional quantum systems is proposed. The system can be driven to an arbitrary target state using cosine classical fields in finite cycles. The control parameters which are time periods of interaction between systems and control fields in each cycle are connected with the probability amplitudes of target states via trigonometrical functions and can be determined analytically.     

Finite-time control of chaotic systems with nonlinear inputs

A finite-time controller is designed for a class of nonlinear systems subject to sector nonlinear inputs. A novel and simple approach is suggested based on the finite-time control principle. The designed sliding-mode controller can drive a chaotic system to track a smooth target signal in a finite time. The chaotic Duffing--Holmes oscillator is used for verification and demonstration.     

An Analog of the Kubo formula for conductivity of spatially inhomogeneous media in spatially inhomogeneous electric fields

The average densities of currents and charges induced by a weak electromagnetic field in spatially inhomogeneous systems at a finite temperature are calculated. The Kubo formula for the electrical conductivity tensor is generalized to spatially inhomogeneous systems and spatially inhomogeneous fields. The contributions containing electric fields and derivatives of the fields with respect to coordinates are separated. It is shown that semiconductor quantum wells, wires, and dots can be treated as spatially inhomogeneous systems.     

智能群体环绕运动控制

自然界中,鸟类迁徙、鱼类群游等群体智能运动具有一定的规律.例如,鸟类迁徙以领导者和跟随者模式的直线运动为主,鱼类中以环绕运动为主.自然界的这种群体直线运动与环绕运动具有十分重要的理论研究价值和广泛的工程应用前景.本文针对群体环绕运动进行研究,考虑个体只能获取局部目标信息这一特性,设计均值估计器进行群体目标状态估计,建立环绕运动算法,确保实现群体圆形编队且保持队形.通过李雅普诺夫理论分析,证明每个个体在有限时间内能获取所有目标平均位置信息,且能基于群体圆形编队队形进行目标环绕和追踪,队形随目标状态变化.有关结果通过仿真得到进一步验证.     

Consensus pursuit of heterogeneous multi-agent systems under a directed acyclic graph

This paper is concerned with the cooperative target pursuit problem by multiple agents based on directed acyclic graph. The target appears at a random location and moves only when sensed by the agents,and agents will pursue the target once they detect its existence. Since the ability of each agent may be different,we consider the heterogeneous multi-agent systems. According to the topology of the multi-agent systems,a novel consensus-based control law is proposed,where the target and agents are modeled as a leader and followers,respectively. Based on Mason’s rule and signal flow graph analysis,the convergence conditions are provided to show that the agents can catch the target in a finite time. Finally,simulation studies are provided to verify the effectiveness of the proposed approach.     

The space of initial conditions and the property of an almost good reduction in discrete Painlevé II equations over finite fields

We investigate the discrete Painlevé equations (dP_II and qP_II) over finite fields. We first show that they are well defined by extending the domain according to the theory of the space of initial conditions. Then we treat them over local fields and observe that they have a property that is similar to the good reduction of dynamical systems over finite fields. We can use this property, which can be interpreted as an arithmetic analogue of singularity confinement, to avoid the indeterminacy of the equations over finite fields and to obtain special solutions from those defined originally over fields of characteristic zero.     

核磁共振中的量子控制

近年来, 随着量子信息科学的发展, 对由量子力学原理描述的微观世界的主动调控已成为重要的前沿研究领域. 为构造实际的量子信息处理器, 一个关键的挑战是: 如何对处于噪声环境下的量子体系实现一系列高精度的任意操作, 以完成目标量子信息处理任务. 为此, 人们将经典系统控制论的思想方法延伸到量子体系的领域, 提出了大量的量子控制方法以及相关的数值技术(如量子优化控制、量子反馈控制等), 并取得了丰富的研究成果. 核磁共振自旋体系具备成熟的系统理论和操控技术, 为量子控制方法的实用性研究提供了优秀的实验测试平台. 因此, 基于核磁共振的量子控制成为量子控制领域的重要方向. 本文简要介绍了量子控制的基本概念和方法; 从系统控制论的角度对核磁共振自旋体系的基本原理和重要控制任务做了阐述; 介绍了近些年来在该领域发展的相关控制方法及其应用; 对基于核磁共振体系的量子控制的进一步的研究做了几点展望.     

基于超表面的多光谱成像系统设计

超表面是一种人工制造的亚波长结构阵列平面,重量轻,易集成,可实现多种功能,被广泛应用于诸多领域。传统光谱成像系统依赖于色散元件及光程累积相位差实现不同波长的色散与聚焦,无法满足系统集成化需求。不同于传统光学元件依赖电磁波在介质中传播累积相位差,超表面依靠界面相位变化来进行相位调控,可实现十分轻薄的光学系统。研究传输相位型超表面,使用时域有限差分算法(FDTD算法)优化单元结构。将超表面引入光谱成像系统中,通过优化亚波长结构尺寸,进行结构排布,开展超表面光谱成像系统研究,实现多波长色散与聚焦独立调控。利用该方法,扫描不同单元结构参数对相位的影响,依照聚焦的相位分布针对不同波长设计对应的位相分布,仿真实现了一个波段范围为510～720 nm,焦距为2 mm,谱段数为八个的超表面多光谱成像系统。通过电磁仿真软件FDTD solutions和数据处理软件计算全模结构电场的远场分布,并分析了系统的成像性能。相比于传统光栅或棱镜分光结构,超表面光谱成像系统可有效减小系统体积,其超轻、超薄、便携特点解决了现有光谱成像系统的应用局限性,为小型化、轻量化光谱成像系统的研制提供了一种新的解决方案。     

Noise and controllability: suppression of controllability in large quantum systems

A closed quantum system is defined as completely controllable if an arbitrary unitary transformation can be executed using the available controls. In practice, control fields are a source of unavoidable noise. Can one design control fields such that the effect of noise is negligible on the timescale of the transformation? Complete controllability in practice requires that the effect of noise can be suppressed for an arbitrary transformation. The present study considers a paradigm of control, where the Lie-algebraic structure of the control Hamiltonian is fixed, while the size of the system increases, determined by the dimension of the Hilbert space representation of the algebra. We show that for large quantum systems, generic noise in the controls dominates for a typical class of target transformation; i.e., complete controllability is destroyed by the noise.     

复杂声学环境中人耳附近空间有源降噪研究综述

复杂声学环境中人耳附近空间降噪是有源噪声控制研究的重要课题,目前采用的主要方法为有源降噪头靠(AHR)和虚拟声屏障(VSB).本文简述AHR与VSB的发展历史和研究现状,介绍其物理原理和设计方法,评述其在实际应用中的优缺点,讨论了目前存在的问题与未来相关的研究方向.已有理论、数值仿真和实验研究验证了相关技术在人耳附近空间产生静区的可行性. AHR系统需要较少控制源,系统相对简单易实现,但静区范围较小,结合虚拟传声器技术和人头跟踪技术后可实现随人头移动的静区,降噪频率可达中高频; VSB产生的静区范围较大,但控制源个数较多,系统复杂和成本高,可通过代价函数和控制源优化,以及主被动混合控制技术来提高有效降噪频率范围和减少控制源个数.     

Finite time stabilization of chaotic systems via single input

In this Letter, we propose a single control input approach for stabilizing three-dimensional chaotic systems in a finite time. The method is more general and is derived from the finite-time stability theory and adaptive control technique; and can stabilize almost all well-known three-dimensional chaotic systems without a prior knowledge of the feedback gain. To show the wider applicability of our method, we give illustrations using different chaotic systems with different structure. Numerical simulations are also used to verify the effectiveness of the technique.     

Adaptive Laguerre filters for active noise control

Feedforward controllers are used in many active noise control (ANC) systems to generate destructive interference in noise fields. An ideal feedforward ANC controller should have an infinite impulse response (IIR) transfer function, but most available feedforward ANC controllers have finite impulse responses (FIR) instead. The main reason is related to the adaptation algorithms of ANC systems. In general, adaptive FIR filters converge faster with guaranteed stability. In this study, the adaptive Laguerre filter is proposed and tested in an ANC application with positive experimental effects. The new ANC controller is an IIR filter, but its adaptation is similar to that of a FIR filter with fast convergence and guaranteed stability. Detailed explanations and analysis are presented in the main text.     

Quantum control with Lyapunov function and bang–bang solution in the optomechanics system

We propose a quantum control scheme with the help of Lyapunov control function in the optomechanics system. The principle of the idea is to design suitable control fields to steer the Lyapunov control function to zero as t → ∞ while the quantum system is driven to the target state. Such an evolution makes no limit on the initial state and one needs not manipulate the laser pulses during the evolution. To prove the effectiveness of the scheme, we show two useful applications in the optomechanics system: one is the cooling of nanomechanical resonator and the other is the quantum fluctuation transfer between membranes. Numerical simulation demonstrates that the perfect and fast cooling of nanomechanical resonator and quantum fluctuation transfer between membranes can be rapidly achieved. Besides, some optimizations are made on the traditional Lyapunov control waveform and the optimized bang–bang control fields makes Lyapunov function V decrease faster. The optimized quantum control scheme can achieve the same goal with greater efficiency. Hence, we hope that this work may open a new avenue of the experimental realization of cooling mechanical oscillator, quantum fluctuations transfer between membranes and other quantum optomechanics tasks and become an alternative candidate for quantum manipulation of macroscopic mechanical devices in the near future.     

Laser pulse design for coherent laser control of potassium atoms

In this paper, the dynamics of coherent laser control of potassium atoms is studied by using the time-dependent multilevel approach (TDMA). The calculation results of population transfer are presented with different laser fields. The results show that the population can be transferred to target state completely by a specially designed laser field.     

Adaptive Fixed-Time Control of Strict-Feedback High-Order Nonlinear Systems

This paper examines the adaptive control of high-order nonlinear systems with strict-feedback form. An adaptive fixed-time control scheme is designed for nonlinear systems with unknown uncertainties. In the design process of a backstepping controller, the Lyapunov function, an effective controller, and adaptive law are constructed. Combined with the fixed-time Lyapunov stability criterion, it is proved that the proposed control scheme can ensure the stability of the error system in finite time, and the convergence time is independent of the initial condition. Finally, simulation results verify the effectiveness of the proposed control strategy.     

一种结合图像复原技术的自适应光学系统控制方法

在天文高分辨成像领域,自适应光学校正和事后图像复原都必不可少,但传统的自适应光学系统控制方法以提升光学成像质量为目的,并未考虑图像复原环节,因此,研究一种结合两者以获得高质量复原图像为目标的控制方法具有重要意义.本文对传统自适应光学技术结合事后图像解卷积的方法进行了分析,阐述了其存在的缺陷.首次提出了将自适应光学技术和图像复原技术相结合进行系统分析的思想,并提出了变形镜校正度(变形镜控制电压相对于传统方法控制电压的缩放比例)的概念,通过改变校正度可实现变形镜校正残差和波前传感器探测误差的调整,同时证明了复原图像质量在校正度下降的方向存在一个最优值,用最优校正度来修正变形镜控制电压,就得到了一种新的控制方法.针对点源目标成像,仿真表明该方法相比于传统方法,能够得到质量更好的复原图像.     

Target-oriented chaos control

Designing intervention methods to control chaotic behavior in dynamical systems remains a challenging problem, in particular for systems that are difficult to access or to measure. We propose a simple, intuitive technique that modifies the values of the state variables directly toward a certain target. The intervention takes into account the difference to the target value, and is a combination of traditional proportional feedback and constant feedback methods. It proves particularly useful when the target corresponds to the equilibrium of the uncontrolled system, and is available or can be estimated from expert knowledge (e.g. in biology and economy).     

Implementation of Controlled‐NOT Gate by Lyapunov Control

A scheme to implement the controlled‐NOT (CNOT) gate for quantum systems is proposed, which is based on Lyapunov control. The scheme does not require precise control of the interaction time since the system is stable when the control fields vanish. In particular, the control fields can be easily obtained by most initial states. As an example, the CNOT gate is realized for two atoms trapped in an optical cavity by exploiting two disturbance cases. Compared to continuous disturbance, the fidelity of the CNOT gate is higher under impulsive disturbance, however, interaction times are much longer. Numerical simulations indicate that the scheme is robust against variations of control parameters and decoherence caused by atomic spontaneous emission and cavity decay. Therefore, the scheme may provide useful applications in quantum computation.     

海洋波导中目标声辐射场的计算方法

针对海洋波导中目标声辐射场的计算问题,提出了一种基于波叠加法并在近、远场采用不同水声传播模型的建模方法,可以将近、远场作为一个统一的系统进行高效地分析。该方法通过给定的已知表面振动速度的结构计算出目标内部虚拟点声源的源强,再配合在相应的水声环境中点声源传播模型的Green函数计算出结构外的声辐射场。以Green函数为纽带,在求源强和计算近场声辐射场时采用镜像虚源法,而在计算远场声辐射场时采用简正波法。通过该方法得到的有限水深波导中声速剖面为正梯度、负梯度、负跃层的3种情况下的脉动球、刚体摆动球的声辐射场计算结果与COMSOL的有限元计算结果进行对比,结果表明了该方法在提高计算效率的同时保证了计算精度。      

一种实用的使用铁磁材料匀场的开放式超导MRI磁体的优化方法(英文)

磁共振成像(MRI)系统是一种重要的医学诊断设备。作者提出了一种针对使用铁磁材料匀场的开放式超导MRI主磁场匀场的优化方法。在这种方法中,为了使这种包含非线性铁磁轭结构的MRI磁体产生高均匀度的磁场,集成了改进的多输入多输出负反馈控制理论和有限元方法,来计算匀场区非线性铁磁材料的形状。特别要指出的是,这种方法对初始值的要求不高,一定可以收敛,如果配置得当,可以快速收敛。另外,由于收敛速度快,这种方法也可以应用于大型的非轴对称三维模型优化分析。在文中,作者在一个二维轴对称磁体模型上测试了该方法,表现良好。