Irreversibility of a quantum walk induced by controllable decoherence employing random unitary operations

Quantum walk is different from random walk in reversibility and interference. Observation of the reduced re- versibility in a realistic quantum walk is of scientific interest in understanding the unique quantum behavior. We propose an idea to experimentally investigate the decoherence-induced irreversibility of quantum walks with trapped ions in phase space via the average fidelity decay. By introducing two controllable decoherence sources, i.e., the phase damping channel (i.e., dephasing) and the high temperature amplitude reservoir (i.e., dissipation), in the intervals between the steps of quantum walk, we find that the high temperature amplitude reservoir shows more detrimental effects than the phase damping channel on quantum walks. Our study also shows that the average fidelity decay works better than the position variance for characterizing the transition from quantum walks to random walk. Experimental feasibility to monitor the irreversibility is justified using currently available techniques.     

Gain Spectrum in an Asymmetric Double Quantum Well

We propose a scheme for light amplification in an asymmetric double quantum well, where two excited states are coupled by resonant tunnelling through a thin barrier in a three-level system of electronic subbands. By applying a single driving laser, the steady state gain can be obtained. The calculated gain spectrum for an asymmetric GaAs/AlGaAs double quantum well structure was presented.     

Ohmic Radio-Frequency Synergy Current Drive and Transformer Recharging Experiments in the HT-7 Tokamak

Lower hybrid current drive (LHCD) experiments for investigating the interaction between lower hybrid (LH) wave and residual dc electric field were performed in extensive plasma parameter ranges in the HT-7 superconducting tokamak. The experimental results are well fitted to the Karney-Fisch theory on the efficiency of LH waves energy converted to poloidal magnetic field energy. The fraction of absorbed LH power is about 0.75 for the HT-7 machine, and the upshift of the LH-wave parallel refraction index during LHCD experiments have been derived by the optimizing fitting parameters. The LH wave is also used for the transformer recharging when the plasma current is maintained unchanged. The highest efficiency about 7% has been achieved in HT-7 machine.     

Fabrication and Characterization of Ni Thin Films Using Direct-Current Magnetron Sputtering

Ni films are deposited by using ultra high vacuum dc magnetron sputtering onto silicon substrates at room temperature, and the high-quality and high-density films are prepared. The parameters, such as thickness, density and surface roughness, are obtained by using small-angle x-ray diffraction (XRD) analyses with the Marquardt gradient-expansion algorithm. The deposition rate is calculated and the Ni single layer can be fabricated precisely. Based on the fitting results, we can find that the surface roughness of the Ni films is about 0.7nm, the densities of Ni films are around 97% and the deposition rate is 0.26nm/s. The roughness of the surface is also characterized by using an atomic force microscope (AFM). The changing trend of the surface roughness in the simulation of XRD is in good agreement with the AFM measurement.     

基于小波变换的混沌信号相空间重构研究

应用小波变换和非线性动力学方法研究了混沌信号在相空间中的行为，指出混沌时间序 列的小波变换实质上是在重构的相空间中，混沌吸引子向小波滤波器向量所张的空间中的投 影，与Packard等人提出的相空间重构方法本质上是一致的.实验结果表明，混沌信号经过 小波变换后，吸引子轨迹与原有轨迹具有相似的结构，同时，系统的关联维数、Kolmogorov 熵等非线性不变量仍然得到保留.这些结果表明，利用小波变换研究混沌信号是有效的. 关键词： 小波变换 相空间重构 混沌信号 脑电信号     

同时实现极坐标变换和径向对数坐标变换的光学方法

本文介绍一种用一维函数坐标变换光学系统,同时实现极坐标变换和径向对数坐标变换的光学方法,给出了实验结果.讨论了在位移、旋转和比例畸变情况下实现不变光学相关的可能方案.     

相干谐波辐射的测量方法和系统

 研究了光学速调管自发辐射谱,其调制率已达0.80,即将进行相干谐波辐射实验。介绍了相干谐波辐射实验的主要考虑因素、相干增强因子的测量方法和测量系统以及种子激光与电子束的准直和同步。     

激光差拍波等离子体加速装置中约束磁场的计算研究

通过对等离子体发生器建立三维模型,计算得到磁场在该装置中的分布情况。所得结果与实际测量基本一致,从而说明所建模型的合理性。通过调节一些参数,对该模型进一步搞清了导致等离子体发生器中真实磁场较实验设计要求偏低的主要原因,并提出了相应的改进方案。     

磁通钉扎液体的动力学特性

依据Ｍａｌｏｚｅｍｏｆｆ和Ｇｒｉｅｓｓｅｎ等建议的表征高温超导体有效钉扎势的唯象表式Ｕ（Ｔ,Ｂ,Ｊ）＝Ｕｏ（Ｔ,Ｂ）／μ（Ｔ,Ｂ）［Ｊｃ（Ｔ,Ｂ）／Ｊ）＾μ（Ｔ,Ｂ）－１］和热激活涡旋运动模型,并通过ＹＢａ２Ｃｕ３Ｏ７－δ薄膜直流传输特性的测量结果,利用“函数唯一性”数据处理方法,研究了钉扎液体的玻璃态指数μ（Ｔ,Ｂ）随温度与外磁场的负值函数形式。以及钉扎势垒Ｕｏ（Ｔ,Ｂ）和Ｊｃ（Ｔ,Ｂ）随外场与