高Tc台阶结Josephson器件

采用预先在衬底上刻蚀出台阶然后原位外延生长高 T_c 超导薄膜的工艺,制备了高 T_c 台阶结 Josephson 器件.文中研究了直流 Josephson 电流对温度和外加微波功率的关系,实验结果与磁通流器件的行为基本相符.     

高温超导本征结的制备工艺和特性

自从本征Josephson效应发现以来,由于其涉及到高温超导材料和结构、Josephson结动力学、高频应用等多个领域,本征结的研究一直是国际上研究的热点之一.我们采用低能离子刻蚀,实现了每分钟和单结本征结厚度相当的刻蚀速率,由BSCCO单晶成功的实现了含有单个或少数几个结的本征Josephson结的制备,并用四端子方法测量其低温下的I-V,Ic-T特性.通过反复实验研究,提高本征结制备的成功率及可重复性,完善制备工艺,并进一步探讨本征结的特性.     

基于高温超导单晶材料的大尺寸约瑟夫森本征结制备工艺研究

基于高温超导单晶材料Bi2Sr2CaCu2O8+x(BSCCO)的约瑟夫森(Josephson)本征结器件制备工艺,成功制备出形貌整齐、特性良好、一致性高的大尺寸太赫兹辐射源本征结器件.从工艺的各个步骤出发,总结了要点,并对原有工艺做出改进.通过扫描电子显微镜观察刻蚀形貌,总结了光刻最佳后烘温度条件,提出了一套重复性好、成功率高的工艺方法.     

MgO衬底上YBa2Cu3O7-δ台阶边沿型约瑟夫森结的制备及特性

MgO衬底上的YBa2Cu3O7-δ(YBCO)台阶边沿型约瑟夫森结(台阶结)在高灵敏度高温超导量子干涉器(superconducting quantum interference device,SQUID)等超导器件研制方面具有重要的应用价值和前景.本文对此类YBCO台阶结的制备和特性进行了研究.首先利用离子束刻蚀技术和两步刻蚀法在MgO(100)衬底上制备陡度合适、边沿整齐的台阶,然后利用脉冲激光沉积法在衬底上生长YBCO超导薄膜,进而利用紫外光刻制备出YBCO台阶结.在结样品的电阻-温度转变曲线中,观测到低于超导转变温度时的电阻拖尾现象,与约瑟夫森结的热激活相位滑移理论一致.伏安特性曲线测量表明结的行为符合电阻分路结模型,在超导转变温度TC附近结的约瑟夫森临界电流密度TC随温度T呈现出(TC-T)^2的变化规律,77 K时JC值为1.4×10^5 A/cm^2.利用制备的台阶结,初步制备了YBCO射频高温超导SQUID,器件测试观察到良好的三角波电压调制曲线,温度77 K、频率1 kHz时的磁通噪声为250μΦ0/Hz^1/2.本文结果为进一步利用MgO衬底YBCO台阶结研制高性能的高温超导SQUID等超导器件奠定了基础.     

超导Josephson隧道结性能和超导量子比特电路的设计方案

超导Josephson隧道结是实现超导量子比特的基本元件。利用悬空掩膜和电子束斜蒸发相结合的工艺方法制备Al/Al2O3/Al超导Josephson隧道结,并且系统研究了底电极、上电极薄膜的厚度及氧化参数等工艺条件与隧道结超导电流密度Jc和面积归一化电阻Rc的关系。设计测量了三种方案的超导量子比特电路,通过对参数和结构的优化测出了较理想的量子比特(qubit)信号。     

第二讲 高温超导约瑟夫森结技术及其应用

高温超导约瑟夫森结技术近年来发展很快，特别是台阶结、双晶结、双外延结、边缘结和邻近效应结等性能已达到实用水平，并应用于超导量子干涉器件、数字信号处理和高频有源器件中。文章介绍了这些结的技术和有关的应用。     

高温超导约瑟夫森结技术及其应用

高温超导约瑟夫森结技术近年来发展很快，特别是台阶结、双晶结、双外延结、边缘结和邻近效应结等性能已达到实用水平，并应用于超导量子干涉器件、数字信号处理和高频有源器件中。文章介绍了这些结的技术和有关的应用。     

应用于低功耗超导电路的Nb基Josephson结和SQUID的制备与测量(英文)

为了突破传统微电子芯片的散热限制和克服超级计算机运算能耗高的困难,低功耗电路已经成为信息计算领域研究的热点问题.近来,Nb基超导数字电路在低功耗电路中显现出比其它方案更有优势的前景.Josephson结的质量在超导数字电路的动态功耗中起着关键的作用.我们采用双层正胶光刻和NR9-3000PY负胶光刻,实现了适用于Nb基Josephson器件的自对准剥离工艺.性能稳定的Josephson结和直流超导量子干涉仪DC-SQUID被制备出来,在不同温度下进行了电学性能测试.不同面积的欠阻尼结具有一致的临界电流密度Jc,在2.54K时约400A/cm2.通过片上施加控制电流的方式,观测了DC-SQUID零电压态跳变电流随磁场的调制效应.     

基于LSAT衬底YBa2Cu3O7-δ台阶结的射频高温超导量子干涉器的制备和表征

基于 YBa2Cu3 O7 -δ (YBCO) 台阶边沿型约瑟夫森结( 台阶结) 的高温超导量子干涉器(Superconducting Quantum Interference Device, 简称 SQUID) 在微弱磁场测量等领域具有重要应用价值. 制 备 YBCO 台 阶 结 及SQUID 的常用单晶衬底包括 LaAlO3 (LAO) 、SrTiO3 (STO) 及 MgO 等. (La0 .3 ,Sr0 .7 ) (Al0 .65 ,Ta0 .35 )O3 (LSAT) 没有孪晶现象、 与 YBCO 的晶格失配度很小(仅为0.4% ) , 有潜力成为制备 YBCO 台阶结及相应的高温超导 SQUID器件的新的衬底选择. 本文首次探索研究了 LSAT 衬底上 YBCO 台阶结型射频超导量子干涉器(rf SQUID) 的制备和表征. 采用氩离子束刻蚀技术在 LSAT(100) 衬底上制备角度约为46°的台阶, 利用脉冲激光沉积法在衬底上生长 YBCO 超导薄膜, 然后利用传统紫外光刻技术制备出高温超导rf SQUID 器件. 在温度为77 K 时, 器件测试观察到幅度较大的电压-磁通特性曲线, 且在部分器件的特性曲线中观察到接近方波的非传统波形, 表明器件工作于噪声较低的色散模式下. 频率1 kHz 时器件的磁通噪声约为20 μΦ0/Hz1/2 , 与文献中报道的 LAO、STO 衬底上台阶结型SQUID 器件的典型结果相当. 本工作展示了利用 LSAT 衬底制备低噪声台阶结型rf SQUID 器件的可行性, 并为进一步研制该衬底上更高性能的高温超导SQUID 器件奠定了基础     

超导Josephson隧道结的制备工艺及性能改善

超导Josephson隧道结是实现超导量子比特的基本元件.本文介绍了一种利用电子束曝光技术和电子束斜蒸发技术相结合的方法来制备铝超导Josephson隧道结.这种方法工艺简单,通过一次光刻就可完成;而且可以通过调节下层光刻胶厚度、斜蒸发角度、悬空桥区宽度等参数可以有效地控制隧道结的面积大小;此外,本方法通过采用不对称电极结构有效地改善了隧道结的漏电流特性,满足了制备超导量子比特的要求.     

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.     

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。     

Peculiarities of rf SQUID response in finite magnetic fields

Single-layer washer-type high-T_c YBa₂Cu₃O_7−x rf SQUIDs with grain-boundary Josephson junctions, as well as low-T_c Nb rf SQUIDs with Nb–Al₂O₃–Nb tunnel junctions, have been investigated in finite magnetic fields. It was shown experimentally that the suppression of the critical current of the Josephson junction due to the magnetic field leads to a modulation of the amplitude of the SQUID output signal. The role of the “unwanted” junction in high-T_c rf SQUIDs, which is formed by the grain boundary running through the washer of the SQUIDs on bicrystal substrates, has also been clarified. The drop of the SQUID signal at a finite magnetic field is originated by the penetration of the magnetic field into the unwanted junction. Based on these results, a direct radio-frequency method for the determination of the first critical field H_c1 for long Josephson junctions has been developed.     

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。     

Spatially resolved gap closing in single Josephson junctions constructed on Bi_2Te_3 surface

Full gap closing is a prerequisite for hosting Majorana zero modes in Josephson junctions on the surface of topological insulators.Previously,we have observed direct experimental evidence of gap closing in Josephson junctions constructed on Bi_2Te_3 surface.In this paper we report further investigations on the position dependence of gap closing as a function of magnetic flux in single Josephson junctions constructed on Bi_2Te_3 surface.     

Continuous Variable Entanglement of Two Mesoscopic Josephson Junctions Induced by a Thermal Radiation Field

The continuous-variable （CV） entanglement between two mesoscopic Josephson junctions is studied and the time-dependent characteristic function in Wigner representation for the Josephson junction subsystem driven by a singlemode thermal field is analytically obtained. It is found that an initial lowest energy state of the junction subsystem can evolve into a two-mode entangled Gaussian state through the interaction with the thermal radiation field. Furthermore, we investigate the influence of the temperature on the entanglement of the junctions and find that the CV entanglement of the two junctions shows the critical behavior with respect to the temperature.     

超导Josephson结直流I-V特性的数值计算

为了研究超导Josephson结的性质,选用四阶龙格-库塔法对RSJ模型下单个Josephson结及其阵列以及微波辐照下Josephson结的直流I-V特性进行了数值计算,并将模拟结果与实验结果进行了比较.     

超导Josephson结直流I—V特性的数值计算

为了研究超导Josephson结的性质，选用四阶龙格一库塔法对RSJ模型下单个Josephson结及其阵列以及微波辐照下Josephson结的直流I-V特性进行了数值计算，并将模拟结果与实验结果进行了比较．     

并联电阻对串联约瑟夫森结阵列相位锁定的影响研究

利用约瑟夫森结阵列制作毫米/亚毫米微波源的一个重要问题是阵列中约瑟夫森结的相位锁定.本文采用仿真的方法研究了约瑟夫森结RCSJ模型存在并联电阻时的相位锁定问题.研究结果包括约瑟夫森结临界电流的不一致性、McCumber参数和结的个数对能够实现相位锁定的参数范围的影响.结果对于约瑟夫森结阵列作为太赫兹产生和检测应用具有重要意义.     

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.