电阻并联约瑟夫森结阵列中的混沌行为

采用数值方法,对存在并联电阻的约瑟夫森结串联阵列进行了研究。首次发现当阵列中结的个数为3时,其中存在明显的混沌行为,并给出了存在混沌行为的参数范围。根据A.A.Chernikov和G.Schmidt的理论,只有当约瑟夫森结的个数大于或者等于4时才能观察到混沌行为;这一发现说明了其理论存在一定的局限性。     

约瑟夫森结与阵列的非线性混沌行为及研究进展

约瑟夫森结是一种利用超导材料制备的新型量子电子器件,它的一个显著特性是具有高度的非线性,因而会出现明显的混沌行为。约瑟夫森结与阵列的混沌行为具有重要的研究和应用价值,受到了广泛的关注。文中对约瑟夫森结与阵列的非线性混沌行为及研究进展做一些介绍。     

本征约瑟夫森结阵列的PSpice模型及混沌行为研究

建立了电容耦合本征约瑟夫森结阵列在电路仿真软件PSpice中的模型，利用这个模型对恒定电流驱动下的本征约瑟夫森结阵列进行了仿真研究.通过与不存在电容耦合的本征约瑟夫森结的时域波形、频谱、分维和相图等结果的对比，发现了本征约瑟夫森结阵列中的混沌行为.这一发现对于本征约瑟夫森结的理论和应用研究有重要的意义.     

基于两级混沌同步保密通信方案的设计

设计了基于混沌双重加密的混沌同步保密通信方案,用以改善保密通信系统的安全性. 一级加密采用了具有2种反馈的同步混沌系统,二级加密采用了超混沌系统. 仿真结果成功地还原了原文信号,证明所设计系统能够更有效的避免现有的基于混沌保密通信破译方法的攻击.     

混沌神经网络逆控制的同步及其在保密通信系统中的应用

利用神经网络的学习、逼近能力构造混沌神经网络，提出逆控制混沌同步方法来同步两个混沌神经网络，并基于逆控制和混沌神经网络的同步给出一种新的混沌保密通信系统.理论分析和数值实验结果表明，新系统能够有效地克服信道噪声对信息传输的不良影响，具有较强通用性和柔韧性，且有同步速度快，信号恢复精度高和密钥量大的优点. 关键词： 混沌同步 自适应逆控制 混沌神经网络 保密通信     

电阻电容分路的约瑟夫森结中阵发性混沌及混沌控制的计算机模拟

通过计算机模拟研究了电阻电容分路的约瑟夫森结中的混沌行为,给出了结电压随阻尼参数及偏置直流电流变化的分岔图,从而展示了混沌产生的方式及混沌出现的参数区间,并基于弱周期扰动理论提出了控制RCSJJ中混沌的方案,模拟结果证明了该方案的有效性.     

现代信息安全与混沌保密通信应用研究的进展

本文首先概述现代保密通信及网络信息安全的主要概念和发展状况，对迄今发展的几种现代著名密码算法进行分析比较；然后综述国际上已经提出的一些典型的混沌保密通信方案及其应用研究的新发展。从通信角度，为了向实用化方向发展，我们将混沌通信研究中常用的混沌遮掩、混沌开关、混沌调制三种主要技术方案，按照实际应用需要，重新把它们分类为三种主要形式，即模-模通信、模-数-模通信和数-数通信，这样便于实际应用，易于借鉴已有知识分析各类通信的性能优劣。在评述性分析了当前国际上三种混沌保密通信方式的典型方案及其进展后，最后简要总结混沌保密通信的一些关键技术，指出今后值得研究的方向，并展望了混沌通信的应用前景。     

一种多通道混沌调相扩频方式及其在水声通信中的应用

直接序列扩频通信是一种低检测概率通信方式,在保密通信中得到了广泛的应用。但该通信方式仍存在缺陷,其采用伪随机序列作为扩频码,而伪随机序列具有周期性和二值性等较为明显的特征,在敌对环境下这些特征可能被利用,使得直扩信号重要的特征参数被估计出来,进而引发信息泄露。针对这个问题,本文提出采用混沌调相序列代替伪随机序列,混沌调相序列是恒包络的复数值序列,可用数量多,相关特性好,而且克服了伪随机序列周期性和二值性的不足,具有更高的保密性。为了提高通信速率,将混沌调相序列与多通道技术相结合,数值仿真结果显示了该通信方式优异的误码率性能,表明该通信方式在水声通信中应用的可行性。     

基于一阶时滞混沌系统参数辨识的保密通信方案

基于参数调制原理,针对一阶时滞Logistic混沌系统设计了相应的参数观测器,仅传递单路信号就可以成功辨识出系统中的未知参数,从而恢复出调制在参数中的模拟信号,并在此基础上采用不同频率信号代替“0”或“1”,设计出具体的数字保密通信方案.数值仿真验证了本方法的有效性. 关键词： 观测器 混沌保密通信 参数调制 滤波     

适合传输快变信息信号的混沌调制保密通信

提出一种新的混沌调制通信方法.利用一个自适应控制器跟踪信息信号的误差对产生混沌载波的发射系统进行参数调制.同时，信息信号直接与混沌载波相乘作为发射信号驱动接收系统.在接收端，另一个自适应控制器维持收发系统的混沌同步并恢复出信息信号.由于同步误差与信息信号无关，从而实现了大幅度、快时变信息信号的混沌调制通信.理论分析和数值模拟的结果表明该方法增强了低维混沌系统的通信保密性. 关键词： 混沌调制 保密通信 自适应控制器 蔡氏电路     

Chaos in Josephson junctions

A detailed analysis of the control space characterization of phase locked states and chaotic attractors in Josephson junctions is presented, based on a model that includes both quadratic damping and cosine interference terms. In addition, some novel features of the nonlinear characteristics of the junction like evolution of basin boundaries, bifurcation structure analysis and scaling behaviour of Lyapunov exponent are discussed.     

Ac Josephson effect in Corbino-geometry Josephson junctions constructed on Bi2Te3 surface

Recently, a Corbino-geometry type of Josephson junction constructed on the surface of topological insulators has been proposed for hosting and braiding Majorana zero modes. As a first step to test this proposal, we successfully fabricated Corbino-geometry Josephson junctions (JJs) on the surface of Bi₂Te₃ flakes. Ac Josephson effect with fractional Shapiro steps was observed in the Corbino-geometry JJs while the flux in the junction area was quantized. By analyzing the experimental data using the resistively shunted Josephson junction model, we found that the Corbino-geometry JJs exhibit a skewed current—phase relation due to its high transparency. The results suggest that Corbino-geometry JJs constructed on the surface of topological insulators may provide a promising platform for studying Majorana-related physics.     

Synchronization of chaos in resistive-capacitive-inductive shunted Josephson junctions

We present a scheme for chaotic synchronization in two resistive- capacitive-inductive shunted Josephson junctions （RCLSJJs） by using another chaotic RCLSJJ as a driving system. Numerical simulations show that whether the two RCLSJJs are chaotic or not before being driven, they can realize chaotic synchronization with a suitable driving intensity, under which the maximum condition Lyapunov exponent （MCLE） is negative. On the other hand, if the driving system is in different periodic states or chaotic states, the two driven RCLSJJs can be controlled into the periodic states with different period numbers or chaotic states but still maintain the synchronization.     

External electric field control in the charge qubits including three Josephson junctions

Based on the standard canonical quantization principle, this paper gives the quantization scheme for the charge qubits mesoscopic circuit including three Josephson junctions coupled capacitively. By virtue of the Heisenberg equation, the time evolution of the phase difference operators across the polar plates and the number operators of the Cooper-pairs on the island are investigated and the modification of the Josephson equation is discussed. The time evolution of the phase difference operators is analysed when the Josephson junctions are irradiated by the external electrical field, which is referred to as also the obtainable controlling parameter.     

超导体/铁磁体绝缘层-超导体隧道结的直流Josephson效应

在超导体铁磁体绝缘层超导体结(SFIS)中,运用BogoliubovdeGennes(BdG)方程和FurusakiTsukada(FT)电流公式,计算铁磁超导共存态的自洽方程和SFIS结中的直流Josephson电流.研究表明,铁磁超导态的磁交换能h对准粒子的Andreev反射有抑制作用,使得SFIS结中的直流Josephson电流随铁磁超导共存态的磁交换能h增大而减弱 关键词： S/F-I-S结 铁磁超导态 直流Josephson电流     

Globally exponential multi switching-combination synchronization control of chaotic systems for secure communications

This article introduces the global exponential multi switching combination synchronization (GEMSCS) for three different chaotic systems with known parameters in the master-slave system configuration. The proposed GEMSCS scheme establishes the global exponential stability of the synchronization error at the origin with different combinations of state variables of the two master chaotic systems with the state variables of a slave chaotic system in diverse manners. Consequently, it increases the complexity level of the information signal in secure communications. To study the GEMSCS, an efficient nonlinear control algorithm is designed. The Lyapunov direct theorem is used to accomplish the global exponential stability of the synchronization error at the origin. The stability conditions are derived analytically. To show the effectiveness and advantages of the proposed GEMSCS control approach, two numerical examples are presented. The computer based simulation results are compared with the reported works in the relevant literature. This article also extends the idea of GEMSCS to the secure communication using the chaotic masking technique. Using the GEMSCS strategy, the information signal is recovered at the receiving system with good accuracy and high speed while the parameters of the transmitter and receiver systems mismatch. At the end, some future research problems related to this work are suggested.     

Anomalous Josephson vortex solutions in Josephson junctions with multiple tunneling channels

We construct a theory for Josephson junction with multiple tunneling channels. We focus on two situations, i.e., a heterotic junction composed of two-gap-superconductor, insulator, and one-gap-superconductor, and a grain-boundary junction formed by two identical multi-gap superconductors. Then, we show that the magnetic field distribution of the Josephson vortex for ±s-wave superconductivity is much more enlarged than that for s-wave without sign change between the order parameters. We display such anomalous vortices and suggest how to evaluate the enlargement.     

Andreev reflection and bound states in topological insulator based planar and step Josephson junctions

A superconductor-topological insulator-superconductor (S/TI/S) junction having normal region at angle θ is studied theoretically to investigate the junction angle dependency of the Andreev reflection and the formation of the Andreev bound states in the step and planar S/TI/S structures. It is found that the Andreev reflection becomes θ dependent only in the presence of the potential barrier at the TI/S interface. In particular, the step and planar TI/S junction have totally different conductive behavior with bias voltage and potential barrier in the regime of retro and specular Andreev reflection. Interestingly, we find that the elliptical cross section of Dirac cone, an important feature of topological insulator with step surface defect, affects the Fabry-Perot resonance of the Andreev reflection induced Andreev bound states (which become Majorana zero energy states at low chemical potential) in the step S/TI/S structure. Unlike the usual planar S/TI/S structures, we find these ellipticity affected Andreev bound states lead to non-monotonic Josephson super-current in the step S/TI/S structure whose non-monotonicity can be controlled with the use of the potential barrier, which may find applications in nanoelectronics.