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.     

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     

高温超导约瑟夫森结阵列的相位锁定

根据交流约瑟夫森效应,研究了嵌入Fabry-Perot谐振腔里的约瑟夫森结阵列在微波辐照下的相位锁定问题。结阵列是由生长在双晶钇稳定氧化锆(YSZ)基片上的YB2Cu3O7(YBCO)超导薄膜光刻成微桥得到的。通过优化设计,在温度为79.2K辐照频率为77.465GHz的条件下,包含620个串联约瑟夫森双晶结的结阵列在外加微波辐照下实现了相位锁定,得到了陡峭的夏皮罗台阶。其第一级夏皮罗台阶的电压约为0.1V,台阶高度约为0.17mA。试验结果表明,这种结阵列结构在电压基准的应用上有极大的优势,而且这种准光学耦合方法在太赫兹信号发生和检测方面有很好的应用前景。     

高温超导双晶结混频器噪声系数测量

噪声系数(Noise Figure,NF)是超导混频器的一个重要参数,是衡量超导混频器内部噪声、影响混频器灵敏度的一个重要指标.实验基于小型脉冲管制冷系统,搭建高温超导约瑟夫森双晶结混频器噪声系数自动测量系统,工作温度为60K.Ar离子刻蚀工艺技术制备高温超导YBa2Cu3O7-δ(YBCO)/MgO约瑟夫森双晶结,通过Y-因子噪声测量法,测量YBCO/MgO约瑟夫森双晶结混频器的噪声系数.实验成功制备了特征电压约1mV的YBCO/MgO约瑟夫森双晶结,在650GHz信号辐照下,有明显的夏皮罗(Shapiro)台阶.在210GHz信号辐照下,进行30次谐波混频,约瑟夫森双晶结在不同偏置电压点中频输出信噪比变化范围约为30dB.在77K与300K不同输入噪声功率下,测得双晶结混频器噪声系数最小值为10dB,偏置电压在300μV.     

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.     

高温超导YBa_2Cu_3O_(7-δ)双晶约瑟夫森结的输运特性随晶界角的变化

高温超导双晶约瑟夫森结在超导电子器件方面具有重要应用,对其输运特性的研究对理解高温超导的d波对称性也有重要意义.我们在晶界角分别为24°、30°和36°的SrTiO_3对称双晶衬底上,利用脉冲激光沉积方法生长了YBa_2Cu_3O_(7-δ)高温超导薄膜,进而利用紫外曝光和离子刻蚀制备了YBCO双晶约瑟夫森结,测量了其输运特性随晶界角的变化.在结样品的超导转变曲线中观测到由双晶晶界引起的电阻拖尾现象,按热激活相位滑移理论对其的分析表明,随着晶界角的增大,YBCO双晶结可能从S-N-S型转变为S-I-S型结.通过伏安特性曲线的测量确定了结的约瑟夫森临界电流Ic、临界电流密度Jc及正常态电阻Rn等特性参数随晶界角的变化,发现近似有标度关系I_cR_n∝J_c~(0.6).随着晶界角的增大,我们观测到Jc随温度下降从单调增加转变为非单调变化,在10K~20K和30K~40K之间出现局部极小值,分析表明这一现象很可能与由YBCO超导能隙的d波对称性所导致的结界面处隙间态的出现相关.     

高温超导量子干涉器中的约瑟夫森结

超导量子干涉器(SQUID)是以约瑟夫森结为核心元件的极其灵敏的磁通-电压转换器.在最近20年间,超导电子学界利用多种铜氧化物高温超导材料,制造出了高温超导约瑟夫森结乃至高温超导量子干涉器(高TcSQUID);特别是,利用YBa2Cu3O7-δ(YBCO)制出了多种高温超导约瑟夫森结,并进而制成了具有一定实用性的高TcSQUID.文章主要是对高TcSQUID中所使用的高温超导约瑟夫森结进行评述.     

利用一种改进模型研究谐振器耦合时的约瑟夫森结的响应(英文)

提出了一种改进的谐振器耦合时的约瑟夫森结模型,模型考虑了结与谐振器之间的耦合强度。利用这种模型,研究了谐振器耦合时的约瑟夫森结的响应,包括单结的电压自锁定和结阵列的相位互锁定现象。研究了耦合强度、谐振器的品质因数和谐振频率对电压自锁定的影响,并给出了合理的解释。此外,还对结阵列的相位互锁定强度对锁定电压和结数量的依赖关系进行了研究,并与理论值进行了比较。所得结果对谐振器耦合下的约瑟夫森结的应用具有指导意义。     

二维约瑟夫森结阵列中的相变及噪声频谱研究

采用电阻分路(RSJ)模型，运用数值计算方法研究二维约瑟夫森结阵列的涡旋度,涡旋密度涨落随温度的变化，表明了超导阵列中存在KTB型相变.还研究了相变点附近的涡旋噪声频谱随温度、驱动电流变化的特性.计算结果与最近实验报导定性一致，并能用涡旋的运动图像来解释噪声频谱的变化规律. 关键词： 高温超导 噪声频谱 约瑟夫森结阵列 KTB相变     

高温超导Josephson结混频器的分析研究

利用高温超导Josephson结已经实现了毫米波、亚毫米波波段的谐波混频.我们通过对高温超导颗粒晶界结、双晶结、内禀结的制备和混频实验对比研究,分析比较了其I-V曲线特性及其在液氮制冷下的混频结果.     

Synchronization of underdamped Josephson-junction arrays

Our recent experiments show that arrays of underdamped Josephson junctions radiate coherently only above a threshold number of junctions switched onto the radiating state. For each junction, the radiating state is a resonant step in the current-voltage characteristics due to the interaction between the junctions in the array and an electromagnetic cavity. Here we show that a model of a one-dimensional array of Josephson junctions coupled to a resonator can produce many features of the coherent be havior above threshold, including coherent radiation of power and the shape of the array current-voltage characteristic. The model also makes quantitative predictions about the degree of coherence of the junctions in the array. However, in this model there is no threshold; the experimental below-threshold region behavior could not be reproduced.Received: 11 April 2003, Published online: 23 July 2003PACS: 74.50.+r Tunneling phenomena; point contacts, weak links, Josephson effects - 85.25.-j Superconducting devices     

Millimeter wave phase-locking in distributed Josephson arrays

Voltage tunable oscillators operating at millimeter and submillimeter wavelengths can be designed and fabricated using series arrays of Josephson junctions. The coherent radiation obtained from such oscillators results from the mutual phase-locking of the junction through the high-frequency Josephson current generated in the array. A 40-junction array of Josephson junctions distributed over many wavelengths has been designed, fabricated and tested for operation at 100 GHz. This paper presents the experimental results obtained for this prototype array. A review of the theory for optimizing array design is presented along the implications for power generation at submillimeter wavelengths in future arrays.     

Quantum coherence in a superfluid Josephson junction

We report a new kind of experiment in which we take an array of nanoscale apertures that form a superfluid (4)He Josephson junction and apply quantum phase gradients directly along the array. We observe collective coherent behaviors from aperture elements, leading to quantum interference. Connections to superconducting and Bose-Einstein condensate Josephson junctions as well as phase coherence among the superfluid aperture array are discussed.     

Observation of high coherence in Josephson junction qubits measured in a three-dimensional circuit QED architecture

Superconducting quantum circuits based on Josephson junctions have made rapid progress in demonstrating quantum behavior and scalability. However, the future prospects ultimately depend upon the intrinsic coherence of Josephson junctions, and whether superconducting qubits can be adequately isolated from their environment. We introduce a new architecture for superconducting quantum circuits employing a three-dimensional resonator that suppresses qubit decoherence while maintaining sufficient coupling to the control signal. With the new architecture, we demonstrate that Josephson junction qubits are highly coherent, with T2 ～ 10 to 20 μs without the use of spin echo, and highly stable, showing no evidence for 1/f critical current noise. These results suggest that the overall quality of Josephson junctions in these qubits will allow error rates of a few 10(-4), approaching the error correction threshold.     

SrTiO3基片上Tl-2212双晶约瑟夫森结的动态特性及噪声影响研究

在SrTiO₃（STO）基片上制作了Tl-2212双晶约瑟夫森结,并对其进行了微波辐照下的I-V特性测试,观察到了夏皮罗台阶,符合约瑟夫森电压-频率关系.利用数值仿真对约瑟夫森结建立了RCSJ模型,仿真结果与实验数据符合较好,利用此模型深入研究了噪声对结动态特性的影响,解释了噪声影响下结的微波感应台阶幅度减小和极小值展宽现象,提出了有效噪声温度为工作温度和外部噪声的等效温度之和. 关键词： RCSJ模型 噪声 Tl-2212双晶约瑟夫森结     

Josephson effect in coherent roton aggregates

A localized microwave electromagnetic field in liquid helium behaves as a laser of rotons: it produces a coherent roton aggregate. We show that the whispering gallery mode of the dielectric resonator excites multiple coherent aggregates simultaneously and predict a Josephson effect between them. The superfluid velocity around the resonator acts as a “voltage across the weak link” in superconducting Josephson junctions. Josephson frequency-velocity relation agrees with existing experimental data.