从金属原子气样本上观察到约瑟夫森效应

1962年由B·D·约瑟夫森首先在理论上预言了电子能通过两块超导体之间薄绝缘层的量子隧道效应，这个预言在一年之后得到了实验上的证实．为表彰约瑟夫森的理论预言，1973年授予他诺贝尔物理学奖，由此普遍称为约瑟夫森效应．该效应的内容得到充实和完善，应用也快速发展，逐渐形成一门新兴学科——超导电子学．两块超导体夹一层厚度适当的薄绝缘材料的组合称S-I-S超导隧道结或约瑟夫森结．约瑟夫森效应分为两种：     

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.     

一种通过约瑟夫森结非线性频率响应确定微波耗散的方法

通过对电流偏置超导约瑟夫森结的微波驱动行为的研究,提出了一个确定约瑟夫森结微波耗散的方法.结的微波耗散由它的品质因子描述.微波耗散严重影响约瑟夫森器件如参量放大器、超导量子比特等的性能.对电流偏置的约瑟夫森结势阱采用四阶近似后,可以得到在较强微波驱动下约瑟夫森结非线性微波响应方程.该方程定量描述了非线性共振频率随外加微波功率变化关系:非线性共振频率与结等离子频率的差别依赖于约瑟夫森结的微波品质因子.对电流偏置的约瑟夫森结的微波运动行为进行了数值模拟.模拟结果确证了微波品质因子与非线性共振频率-等离子频率差别的定量关系可以应用于约瑟夫森结中.用这种非线性频率响应方法来确定约瑟夫森结的微波耗散没有严格的温度要求,可在单个电流偏置的结中完成,实验上具有简单可靠性.     

超导约瑟夫森结物理参数的实验推算

超导约瑟夫森结是实现超导量子计算和微波单光子探测的核心器件,其物理参数很难直接测定.与之前常用的测量结微波激励效应估计方法不同,本文通过实验测量低频电流驱动下的约瑟夫森结Ⅰ-Ⅴ曲线及其跳变电流统计分布,并与基于标准电阻电容分路结模型数值模拟进行比对,推算出了约瑟夫森结的临界电流I_c、电容C、电阻R及阻尼参数β_c等物理参数.结果表明,所推算的参数值与基于微观理论推导所得到的Ambgaokar-Baratoff公式基本符合,可供约瑟夫森结的器件参数按需设计和制备工艺的参数设置等参考.     

垫圈样式的约瑟夫森结

垫圈是与螺栓、螺母配套使用的金工零件．试想，将三个大小相同的垫圈叠在一起：两个超导Nb垫圈，中间夹一个极薄的绝缘垫圈(AJOx)，便构成了一个环形约瑟夫森结．最近，来自德国爱尔兰根一纽伦堡大学的wallraff等研究了这样一种“长约瑟夫森结”中的涡流动力学特性．结果表明，这类涡旋有可能成为未来量子计算中量子比特的候选者．     

嵌入Fabry-Perot谐振腔的高温超导双晶约瑟夫森结的毫米波辐照特性研究

采用嵌入Fabry-Perot谐振腔的方式,研究了Tl2Ba2CaCu2O8(Tl-2212)高温超导薄膜双晶约瑟夫森结的毫米波辐照特性.重点研究了双晶约瑟夫森结与Fabry-Perot谐振腔的耦合特性,发现放置在谐振腔中的结的位置、角度、结的图形以及Fabry-Perot谐振腔中两镜面间的距离等对耦合都有很大的影响.通过精细调节这些参数,可使双晶约瑟夫森结与外加毫米波达到最佳耦合.在最佳耦合情况下,能观察到9级明显的夏皮罗台阶.利用Fabry-Perot谐振腔技术,解决了约瑟夫森结与毫米波的耦合问题,为高温超导约瑟夫森结的毫米波及太赫兹波的辐射和检测研究奠定了基础.     

高温超导双晶约瑟夫森结阵列毫米波相干辐射

研究了嵌入Fabry-Perot谐振腔的高温超导双晶约瑟夫森结阵列毫米波相干辐射的实验结果.相干辐射是通过约瑟夫森结阵列与基片(作为一个介质谐振器)和Fabry-Perot(FP)谐振器的共同作用实现的.由166个高温超导双晶约瑟夫森结串联阵列在77 K温度下产生的相干辐射,辐射峰的中心频率为75.84 GHz,功率大约为10 pW. 关键词： 高温超导薄膜 Fabry-Perot谐振腔 约瑟夫森结 毫米波辐射     

嵌入到Fabry-Perot谐振腔的双晶约瑟夫森结阵列的阻抗匹配和相位锁定研究

在He等人所做的嵌入到Fabry-Perot谐振腔中约瑟夫森结阵列的微波辐照研究基础上,提出了同时实现约瑟夫森结阵列阻抗匹配和相位锁定的方法,进行了相关的电磁仿真和数值计算.双晶约瑟夫森结阵列被制作在YSZ双晶基片上,同时被嵌入到Fabry-Perot谐振腔内.通过在基片上制作与结阵列集成的串联馈电半波偶极天线阵,并对其结构进行优化实现了结与天线的匹配,数值计算表明结的辐射效率达到94%;利用天线阵辐射场的特征和对模型合理的设计,使Fabry-Perot谐振腔和基片同时谐振在合适的模式下,从而使结阵列与谐 关键词： 约瑟夫森结阵列 阻抗匹配 相位锁定 Fabry-Perot谐振腔     

基于高温超导双晶结的约瑟夫森效应观测实验

基于YBa2Cu3O7-δ高温超导双晶结,组建了约瑟夫森效应测试装置.利用此装置观察了直流和交流约瑟夫森效应,并测量了约瑟夫森结的临界电流和夏皮罗台阶.     

SNS与SINIS结阵制作工艺的比较

国家电压基准是基于约瑟夫森量子化效应的。传统的SIS结阵具有不能快速选择特定的台阶,相位锁定时间短的问题。I-V曲线无回滞的约瑟夫森结阵,其I-V曲线单值,电压台阶宽,解决了SIS结阵的问题。美国标准技术研究院的Hamilton提出并制作高度阻尼的可编程SNS约瑟夫森结阵电压标准;德国物理技术研究院则选择SINIS结来制作可编程约瑟夫森结阵电压基准。从结构、性能和制作方法等方面对SNS和SINIS可编程约瑟夫森结阵进行了比较。     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Research on beamforming method for dual-line array with space mismatch between the two line arrays

The performance of port/starboard discrimination of dual-line array will be seriously degraded when the space between the two line arrays of the dual-line array is mismatched. The directivity function of the delay-sum and delay-subtract beamforming is deduced and the port/starboard discrimination of the delay-sum and delay-subtract beamforming is also studied both under the ideal status and the status under which the space between the two line arrays of the dual-line array is mismatched. Analysis results show the delay-subtract beamforming has better performance of port/starboard discrimination. At last, the sea trial results demonstrate the theoretical results.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Retrieval of ultraviolet skylight radiances and O3 slant column densities from balloon-borne limb spectrometer

With a novel light-weight and absolutely calibrated ultraviolet （UV） spectrometer, UV skylight radiances and O3 slant column densities are measured by balloon-borne limb measurements in Xinjiang area, China. UV skylight radiances measured at the height of 31 km are compared with the results from Modtran in the wavelength range from 290 to 420 nm. O3 slant column densities are derived from radiance spectra in the Huggins bands （320 - 335 nm） using differential optical absorption spectroscopy method. And the parameter exhibits a good correlation with the same value simulated by radiative transfer model （Tracy）. The O3 profile simultaneously measured by an O3 sonde is used as input in Tracy calculations. The O3 sonde is launched on the same balloon.     

Design optimization of highly sensitive LSPR enhanced surface plasmon resonance biosensors with nanoholes

For breaking through the sensitivity limitation of conventional surface plasmon resonance (SPR) biosensors, novel highly sensitive SPR biosensors with Au nanoparticles and nanogratings enhancement have been proposed recently.But in practice, these structures have obvious disadvantages.In this study, a nanohole based sensitivity enhancement SPR biosensor is proposed and the influence of different structural parameters on the performance is investigated by using rigorous coupled wave analysis (RCWA).Electromagnetic field distributions around the nanohole are also given out to directly explain the performance difference for various structural parameters.The results indicate that significant sensitivity increase is associated with localized surface plasmons (LSPs) excitation mediated by nanoholes.Except to outcome the weakness of other LSP based biosensors, larger resonance angle shift, reflectance amplitude, and sharper SPR curves' width are obtained simultaneously under optimized structural parameters.     

Polymer gratings based on photopolymerization for low-order distributed feedback polymer lasers

Novel polymer distributed feedback(DFB)gratings are fabricated based on photopolymerization to reduce lasing threshold of polymer lasers.A photopolymer formulation sensitive to 355-nm ultraviolet(UV)light is proposed for the fabrication of polymer gratings and it can be used to form polymer films by spin-coating process.A very low surface-relief depth ranging from 12.5 to about 1.0 nm has been demonstrated with a refractive-index modulation of about 0.012.The experimental results indicate that such polymer gratings have promising potentials for the fabrication of low-order DFB organic semiconductor lasers.     

A novel methodology for photometric compensation of projection display on patterned screen

We propose a novel methodology based on the projector-camera (ProCam) system to address the photometric compensation issue for the projection display on the patterned screen.The patterned screen is treated as the combination of a perfect white screen and a color modulator.The perfect white screen is used to automatically and accurately characterize the ProCam system offline using the polynomial model,and the parameters of the color modulator can be efficiently recovered by employing only two gray images based on the linear reflectance model.The experimental results show that the color artifacts of the display image can be greatly improved with this methodology,which demonstrates its feasibility and validity in the photometric compensation.