Single Electron Transport and Entanglement Induced by Surface Acoustic Waves versus Free Ballistic Propagation in Coupled Quantum Wires

In this work we study the coherent propagation of electrons in quantum wires driven by surface acoustic waves, as a part of a feasibility study on a coupled quantum wires device, able to realize the basic operations needed for quantum computing. We demonstrate that the introduction of the surface acoustic wave is able to improve the devices performance. In particular, single- and double-qubit quantum gates have been simulated and better results are obtained, with respect to the free electron propagation. A further analysis reveals a strong reduction of the final undesired spatial entanglement and confirms the effectiveness of the dynamics driven by surface acoustic wave.     

输电线路行波仿真方法及行波试验技术

围绕输电线路行波测距装置性能试验方法问题,分析影响测距装置感受行波的因素,提出行波传播全过程仿真概念,给出用两端口网络描述电流互感器行波传变特性的方法,实现了包括输电线路故障、电流互感器传变、二次电缆传播、二次负荷模拟的行波传播全过程仿真,仿真获得的行渡波形与现场记录行波波形相似.针对工程应用完成行波传播全过程仿真,利...     

Application of the R-matrix method in quantum transport simulations

The R-matrix method based on a continuous model is generalized as to become applicable to the atomistic transport simulations with a tight-binding device Hamiltonian. The device elements are introduced as arbitrary atomic clusters in the device area and freedom in the device fragmentation can be used to reduce computations. In the ballistic regime, the best computer performance is achieved by taking individual atoms as the device elements. Non-equilibrium current carrying electronic states are constructed by the forward-backward R-matrix propagation scheme which does not require large computer operations and mass storage. The method is applied to quantum transport in p-Si nanowire with random vacancies and surface roughness.     

Surface roughness induced device variability: 3D <Emphasis Type="Italic">ab initio</Emphasis> Monte Carlo simulation study

It is expected that published results from drift diffusion simulation of oxide thickness fluctuations in nano-scale devices underestimates the true intrinsic device parameter variation by neglecting local variations in surface roughness scattering. We present initial results from 3D ‘bulk’ Monte Carlo simulation including an ab initio treatment of surface roughness scattering capable of capturing such transport variation. The scattering is included directly through the real space propagation of carriers in the fluctuating potential associated with a randomly generated interface. We apply this approach to simulate inversion layer mobility in order to validate the model before its possible application in device variability simulations. Qualitative agreement is found with universal mobility data and avenues for possible calibration of surface and simulation parameters are highlighted.     

Towards Fully Quantum Mechanical 3D Device Simulations

We present a simulator for calculating, in a consistent manner, the realistic electronic structure of three-dimensional heterostructure quantum devices under bias and its current density close to equilibrium. The electronic structure is calculated fully quantum mechanically, whereas the current is determined by employing a semiclassical concept of local Fermi levels that are calculated self-consistently. We discuss the numerical techniques employed and present illustrative examples that are compared with quantum transport calculations. In addition, the simulator has been used successfully to study shape-dependent charge localization effects in self-assembled GaAs/InGaAs quantum dots.     

电力系统连续体模型中机电波传播特性研究

该文根据电力系统连续体模型中线性化的波动方程，用解析方法研究机电波的传播特性。根据Peterson法则，研究连续体模型中的集中参数元件发电机对机电波传播过程中反射和透射的作用，证明连续体电力系统的机电动态能表达为机电波在连续体2端多次反射和透射过程的叠加，为从机电波传播的角度揭示电力系统机电动态的内在机理建立了一定的基础。最后通过对1个实例的仿真分析，证实该文理论的正确性。     

基于后选择的连续变量量子密钥分发协议

连续变量量子密钥分发（CVQKD）是利用连续变化的物理量承载密钥的量子密钥分发协议,与电力系统普遍采用的离散变量量子密钥分发协议相比,其具有设备简单、探测效率高、兼容性好等优点,成为量子密钥分发的研究热点。然而,量子态在量子信道中的传输衰减严重限制CVQKD传输距离。提出了一种基于后选择方法的CVQKD协议,且不需要额外的单光子源。研究结果表明,该后选择方法中测量值越大的物理量被保留下的概率越高。该方法可以简化并降低连续量子密钥分发协议实现的成本,为探索出电力网络的量子保密通信方案提供研究思路。     

Robust Computational Models of Quantum Transport in Electronic Devices

A family of efficient quantum transport models for simulation of modern nanoscale devices is presented. These models are used for quantitative calculations of quantum currents in nanoscale electronic devices within our device simulator software. Specifically, we used them to simulate the tunneling current through thin barrier in vertical-cavity surface-emitting laser (VCSEL), direct and reverse tunnel currents through the tunnel junction, Schottky contact characteristics, and gate induced drain leakage (GIDL).     

基于量子神经网络的电力电子电路故障诊断

针对电力电子电路故障诊断时故障模式间存在交叉数据的模式识别问题,在量子计算和人工神经网络结合的基础上,提出了一种基于量子神经网络的故障诊断方法,并以双桥12相脉波整流电路为例进行故障诊断.实验结果表明:量子神经网络有一种固有的模糊性,它能将不确定性数据合理地分配到各故障模式中,从而使网络具有高性能、更好的鲁棒性和省时的特点,且能正确地识别大部分的样本故障模式,成功地完成电力电子电路的故障诊断.     

Stochastic modelling of target detection and tracking in surface wave HF radars

In this study, a software package is described which has been developed for the simulation of detection and tracking in surface wave high frequency (SW-HF) radars. The aim is to investigate the problems related to detection and tracking of surface targets at beyond the horizon ranges. In SW-HF radars target detection and tracking involves stochastic features such as target RCS fluctuations, atmospheric, galactic and/or man-made ambient interference components, and the sea clutter with the dominant resonant Bragg returns which affect target detection are all incorporated in the package. In the model, first, terrain data are fed into the simulator by means of a specially designed graphical user interface. Then, a scenario is prepared where the radar's location, coverage and operational parameters can be defined, together with different targets and their sailing routes. The radial propagation paths for angular resolution cells are extracted from the terrain data with the lengths of (possible) sea–island transitions. The surface wave path losses are calculated over the smooth spherical earth's surface with finite conductivity. Surface roughness and mixed-path propagation effects are also included in these calculations. The target detection is performed in the frequency domain after calculation of the noise floor, signal to noise (SNR) and clutter to noise (CNR) ratios. Since SW-HF radars yield coarse range and azimuth but accurate velocity measurements, different Kalman filter techniques are applied for the target tracking, and algorithms are added to improve the track–measurement data correlation. Various simulation tests are performed and the results are presented. © 1998 John Wiley & Sons, Ltd.     

Electronic structure and transmission characteristics of SiGe nanowires

Atomistic disorder such as alloy disorder, surface roughness and inhomogeneous strain are known to influence electronic structure and charge transport. Scaling of device dimensions to the nanometer regime enhances the effects of disorder on device characteristics and the need for atomistic modeling arises. In this work SiGe alloy nanowires are studied from two different points of view: (1) Electronic structure where the bandstructure of a nanowire is obtained by projecting out small cell bands from a supercell eigenspectrum and (2) Transport where the transmission coefficient through the nanowire is computed using an atomistic wave function approach. The nearest neighbor sp³d⁵s^* semi-empirical tight-binding model is employed for both electronic structure and transport. The connection between dispersions and transmission coefficients of SiGe random alloy nanowires of different sizes is highlighted. Localization is observed in thin disordered wires and a transition to bulk-like behavior is observed with increasing wire diameter.     

无损传输线网格线离散格式行波数学模型及其数值解法

为深入研究行波在配电线路上的传播特性,建立了时间-空间网格线离散格式的无损传输线行波数学模型,采用偏微分方程的数值解法推导了波动方程的稳定条件和边界条件,并尝试对边界条件进行简化,以实现电压和电流的完全解耦。文章还给出了离散格式波动方程时间和空间步长的选取条件,即两者以波速为关联,一一对应。在单根线模型的基础上,结合行波折反射定律,以T型线路为例给出了节点边界条件,并通过仿真实现了该线路的行波往返过程。理论推导和仿真实验证明了所提算法的正确性。     

Full Quantum Mechanical Simulation of Ultra-Small Silicon Devices in Three-Dimensions: Physics and Issues

The combination of the need for alternative devices and the improvement in process technology has led to the examination of silicon quantum wires for future MOS technology. However, in order to properly model these devices, a full three-dimensional quantum mechanical treatment is required. In this paper, we present the results of a three-dimensional, fully quantum mechanical, self-consistent simulation of a silicon quantum wire MOSFET (Metal Oxide Field Effect Transistor) with a narrow channel (8 nm). A quasi-standing wave is formed in the narrow channel at certain gate voltages as the electron density is trapped in narrow channel. These effects are the result of two competing effects: (1) the interaction of the propagating electrons with the channel dopants, as well as with the dopants in the source and drain of the device. (2) the reflections from the boundaries that form the narrow channel both on the source side and the drain side.     

A Quantum Mechanical Approach for the Simulation of Si/SiO2 Interface Roughness Scattering in Silicon Nanowire Transistors

In this work, we present a quantum mechanical approach for the simulation of Si/SiO₂ interface roughness scattering in silicon nanowire transistors (SNWTs). The simulation domain is discretized with a three-dimensional (3D) finite element mesh, and the microscopic structure of the Si/SiO₂ interface roughness is directly implemented. The 3D Schrödinger equation with open boundary conditions is solved by the non-equilibrium Green’s function method together with the coupled mode space approach. The 3D electrostatics in the device is rigorously treated by solving a 3D Poisson equation with the finite element method. Although we mainly focus on computational techniques in this paper, the physics of SRS in SNWTs and its impact on the device characteristics are also briefly discussed.     

Characterization of RF sputtered zinc oxide thin films on silicon using scanning acoustic microscopy

Zinc oxide (ZnO) thin films were grown on silicon (100) substrate using radio frequency (RF) sputtering under various processing parameters including deposition time and annealing temperature. A series of characterization techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and scanning acoustic microscopy (SAM) have been used to analyze the crystallinity and crystal orientation, structural morphology, surface roughness, and acoustic properties of these films. In particular, quantitative analysis of elastic wave propagation in ZnO thin films by scanning acoustic microscopy has been performed for the first time in the present work. It has been shown that the propagation properties of acoustic waves on the surface of ZnO thin films strongly depend on film thickness, crystallinity, and surface roughness. The dispersion properties of surface acoustic waves (SAWs) are observed as a function of ZnO film thickness. The velocities of SAWs range from 5328.3 m/s to 4245.7 m/s with increasing film thickness from 32.5 nm to 2.04 μm, while smoother surface contributes to faster propagation of SAWs.     

基于模量行波传输时间差的线路接地故障测距与保护

随着输电线路电压等级的不断升高,基于行波原理的故障测距和超高速线路保护已经成为目前研究的热点。通 过对接地故障时零模和线模行波传输规律的分析,得出以下结论：1）零模检测波速度和波头李氏指数之间具有特定对应关系;2）零模和线模行波分量传输时间差与传输距离之间具有单调非线性递增关系;3）阻波器对零模和线模电压行波分量的影响不同,模量传输时间差在区内末端和区外出口故障时具有突变特性。根据以上分析,利用小波变换和BP神经网络技术,导出了基于零模和线模传输时间差的接地故障测距、单端量保护新算法,并利用ATP中考虑频散特性的线路模型进行了仿真,仿真结果证实了上述算法的有效性。     

A new approach for numerical simulation of quantum transport in double-gate SOI

Numerical simulation of nanoscale double-gate SOI (Silicon-on-Insulator) greatly depends on the accurate representation of quantum mechanical effects. These effects include, mainly, the quantum confinement of carriers by gate-oxides in the direction normal to the interfaces, and the quantum transport of carriers along the channel. In a previous work, the use of transfer matrix method (TMM) was proposed for the simulation of the first effect. In this work, TMM is proposed to be used for the solution of Schrodinger equation with open boundary conditions to simulate the second quantum-mechanical effect. Transport properties such as transmission probability, carrier concentration, and I–V characteristics resulting from quantum transport simulation using TMM are compared with that using the traditional tight-binding model (TBM). Comparison showed that, when the same mesh size is used in both methods, TMM gives more accurate results than TBM. Copyright © 2007 John Wiley & Sons, Ltd.     

Use of the scattering matrix for device simulations

The use of the quantum mechanical scattering matrix is a time proven method for determining the transport probability for an electron wave in a nanostructure. When coupled with the Landauer formalism, it provides a valuable approach for simulation of semiconductor devices. Here, we discuss a numerically stable method to solve this transmission problem in a recursive manner. It is easily extended to dissipative and far from equilibrium situations. We also discuss the use of scattering matrices in photo excitation of nanostructures.     

电力生产业务的量子广域网加密技术研究

针对电力生产业务的通信特点以及安全需求,提出了基于量子通信卫星的电力天地一体量子保密通信方案,并且针对地面链路中电力架空环境下长距离量子通信的问题,提出采用线路偏振无关的Faraday-Michelson型量子密钥分配系统的方案,并通过试验证明了方案在电力应用环境中的可行性,最后对电力架空环境下的相位补偿技术做出了分析。