10V约瑟夫森结阵电压基准

在 1V约瑟夫森结阵电压基准的基础上 ,10 V约瑟夫森结阵电压基准于 1999年底在中国计量科学研究院量子部电压实验室建立。其校准电压在 0 .1V～ 10 V范围内连续可调。校准固态电压标准 10 V输出值的合成不确定度为 5.4× 10 -9(1σ)     

交流约瑟夫森电压合成装置的研究

设计制作了一套交流约瑟夫森电压合成装置(JAWS),能够驱动1 V SINIS型可编程约瑟夫森结阵合成峰值1.2 V、 200 Hz以下频率的交流量子电压。实验结果表明,该装置能够合成200 Hz以下频率的交流量子电压,且合成60 Hz交流电压的不确定度优于5×10^-6,为进一步开展我国首个交流量子电压基准的研究工作奠定了基础。     

10伏约瑟夫森结阵电压基准获国家科技进步奖

我院研制的“10伏约瑟夫森结阵电压基准”装置，荣获2003年度国家科技进步奖二等奖。     

约瑟夫森结工艺系统

超导电子学和超导量子信息等领域的核心元器件是约瑟夫森结,这是一种超导体/介质层/超导体三层结构的非线性器件.超导量子比特常用铝/氧化铝/铝结构的结,在量子芯片上制备这种约瑟夫森结,需要在衬底不离开真空环境的条件下,实施离子束刻蚀、样品方位角可调的电子束蒸发、气氛可控氧化等工艺过程.自主研发的约瑟夫森结工艺系统是一套集成...     

我国的1V及10V约瑟夫森量子电压基准装置

文章描述了我国量子电压基准的建立、发展、现状和所取得的成果,以及与国际计量局进行基准关键比对的情况。     

约瑟夫森结阵器件的研究进展

介绍了约瑟夫森效应在电压基准方面的应用,综述了目前国内外对用于电压基准的约瑟夫森结阵的研究和发展过程,重点介绍了国内用于电压基准的Nb/NbxSi1-x/Nb单结的研究进展。     

国家电压副基准近年来的变化：用约瑟夫森电压标准进行监测

自１９９３年１Ｖ结阵约瑟夫森电压标准正常运行以来，就开始对国家电压副基准进行了连续的监测。经过近四年的连续测量发现：国家副基准电池组０５１中的十个标准电池的电动势都呈上升趋势，其中最大的０５１－２达到０．２０４μＶ／年，最小的０５１－８达到０．０４４μＶ／年，十个标准电池的电动势的算术平均值的变化速率为＋０．０８１μＶ／年，并且随时间几乎成直线上升关系。     

可编程约瑟夫森结阵偏置组合算法研究

在可编程约瑟夫森量子电压标准系统中,快速并准确地计算各约瑟夫森子结阵的偏置状态是实现量子电压精准输出的前提。传统的枚举-索引算法通过遍历所有可能的偏置组合以寻找最优解,因此计算效率较低,难以适应量子电压非周期性连续变换输出等特殊应用场景。基于此,提出了一种面向三进制可编程约瑟夫森结阵的偏置组合算法。首先根据各子结阵中包含的约瑟夫森单结数量特征对子结阵进行自适应分组,并据此快速计算预偏置组合;进一步地,结合近似计算方法和量化误差补偿方法,克服预偏置组合中可能存在的子结阵失效、亚分辨率设计等特殊问题。实验结果表明,该算法在多种条件下均能找到最优偏置组合,并且计算效率明显优于传统的枚举-索引算法。     

约瑟夫森结Nb电极的实验研究

通过溅射Ｎｂ膜张力与氩（Ａｒ）压强的关系，超导转变温度Ｔｃ，室温阻抗与液氮温度阻抗比ＲＲＴ／ＲＬＮ２，沉积中Ａｒ浓度ＣＡｒ与负偏压关系的测量和扫描电子显微镜的观察分析，对约瑟夫森结Ｎｂ电极作了研究。发现Ａｒ压强在１．１Ｐａ时，Ｎｂ膜呈现无应力状态；低负偏压下沉积的Ｎｂ膜晶粒结构是由致密膜到圆柱状。在偏压Ｕｂ＝－５０Ｖ时，获得表面致密均匀、晶粒结构合适的Ｎｂ膜。对Ｎｂ膜用阳极氧化电压谱图（ＡＶＳ）分     

Operation of NIST Josephson Array Voltage Standards

This paper begins with a brief discussion of the physical principles and history of Josephson effect voltage standards. The main body of the paper deals with the practical details of the array design, cryoprobe construction, bias source requirements, adjustment of the system for optimum performance, calibration algorithms, and an assessment of error sources for the NIST-developed Josephson array standard.     

基于SNS型双路约瑟夫森结阵驱动方法研究

根据SNS型双路约瑟夫森结阵的驱动原理以及结阵分段特点,提出了平衡三进制驱动算法,实现了双路约瑟夫森结阵偏置状态的快速计算。根据约瑟夫森结阵的偏置状态以及组合方式,采用节点电压法,准确合成了双路阶梯波交流量子电压的台阶电压值,最终实现了最小分辨率为2个结,有效位为15位的交流量子电压输出。双路交流量子电压互测实验结果表明,合成交流量子电压的最大误差为0. 06μV,双路信号同步性测试实验中,两个通道的相位差为-0. 01μrad,证明了合成双路交流量子电压具有较高的幅值准确度和相位同步性。     

The kosterlitz-thouless transition and vortex dynamics

The physics of the Kosterlitz-Thouless vortex-unbinding transition in two-dimensional superfluids is discussed, and theN ×N Josephson junction array is considered as a prototype system. Dynamical behaviour is considered in two cases: (a) the complex impedance shows structure at a frequency-dependent transition temperature, similar to the dynamic susceptibility of a spin glass; (b) with a perpendicular non-uniform magnetic field, of a particular ‘self-similar’ hierarchical pattern, a scaling argument gives non-exponential relaxational dynamics of a prepared non-equilibrium vortex distribution.     

Percolative behavior of transport properties in granular high-Tc superconductors

A new model based on percolative computation directly performed for an array system of Josephson junctions is reported. The number of percolative paths is obtained and the total critical current of the model system is estimated from 2D and 3D arrays at selected values of external magnetic field. The evolution of the critical current distribution of the junctions at increasing magnetic field is studied in view of the relevance in percolative path calculations and compared with the experimental distribution obtained fromI– V characteristics. Percolative simulation results are shown to reproduce more satisfactory experimental critical current behavior in external magnetic fields, obtained in highly porous thick YBa₂Cu₃O_7-x films electrophoretically deposited than mere statistical averages.     

Periodic Properties of Voltage Versus Applied Magnetic Flux Curves in Elementary Cubic Networks of Josephson Junctions

We study the periodicity properties of a homogeneous elementary three-dimensional network of Josephson junctions in the presence of linear and shear strain of the cubic structure. We find that, for small values of the strain parameters, the system still retains periodicity in the voltage versus applied field curves. In addition, we see that these periodicities can be analytically related to the value of the period of a homogeneous and symmetric cubic network of Josephson junctions. Therefore, we argue that the system, even when subject to small structural deformations, shows robustness in the periodic behaviour of its observable electrodynamic quantities.     

Numerical simulation of collective phenomena in Josephson junction networks

Collective pinning phenomena of vortices in Josephson junction networks (JJN) in magnetic fields are studied using numerical simulations. We consider two kinds of structure of JJN: a ladder (Josephson junction ladder, JJL) and a two-dimensional square array (Josephson junction array, JJA). For the JJL and JJA with distribution of the strengths of junction critical currents, we investigate the critical current of vortex depinning in the presence of bias currents. On the basis of a theory of collective vortex pinning, it is found that the critical currents for both JJL and JJA show a universal scaling behavior.     

Static Magnetic Flux Dynamics in One-Dimensional (1D) Josephson Lattices

We investigated static magnetic flux dynamical properties of one-dimensional lattices of Josephson junctions. The discretized wave equations of the Josephson junction lattice were solved using a generalized relaxation iteration algorithm. Numerical simulations indicated that transitions between periodic state and chaotic state will occur as the physical parameters and geometric parameters such as external current y _n, magnetic field h ₀, h, and the length of Josephson junction _n and d _n , varied. A shot length of the Josephson junction favors stable periodic states.     

Mechanical properties of In-based eutectic alloy solders used in Josephson packaging

InBiSn and InSn eutectic alloy solders are used in the packaging of the cryogenic Josephson processor. The ductile behaviour of these alloys is important to the application of joints which experience large thermal stresses. In order to characterize the mechanical behaviour at cryogenic temperatures, tensile and shear strengths of bulk solders were measured at and below room temperature. It is found that the ultimate tensile and shear strengths of bulk solders increase as temperature decreases. At low temperatures, the ultimate tensile strength of InBiSn alloy is about three times less than that of InSn alloy. The ductility of both alloys reduces at low temperatures. The fracture surfaces of both bulk solders and solder joints having an interface material (Pd and Au thin films) to the electrical contact pads (Nb thin film) were examined using SEM. Ductile fracture mode was observed for all the specimens down to liquid nitrogen temperature.     

Simulations of Phase Slippage in an Aperture Array

To understand the origins of synchronous and asynchronous phase slippages observed in an array of apertures connecting two reservoirs of superfluid ⁴He, we have investigated the role of thermal fluctuations in the critical velocity and the possible effects of having an array rather than a single aperture through several model simulations. The results are compared with recent experiments carried out near the superfluid transition temperature with an array of apertures as well as those carried out at low temperatures with a single aperture.