自对准法制备Nb/AlO_x/Nb超导Josephson结及其直流特性测试

超导量子比特系统是实现大规模量子计算的可行方案之一。该文采用集成电路平面工艺制备了基于Nb/AlOx/Nb 3层膜结构的超导Josephson结,为制备性能可靠的超导量子比特提供了一定基础。工艺中采用了自对准技术形成结区,从而有效地保护器件结构并降低了工艺复杂度。搭建了超导Josephson结直流特性低温测试系统,并对制备的Josephson结进行了直流特性测试,得到Josephson结在不同温度下的伏安特性,并观察到铌(Nb)的超导能隙电压2.85mV的跳变。同时,测量得到Josephson结临界电流随温度变化的关系,与Ambegaokar和Baratoff的理论结果相符合。     

Josephson效应与Josephson方程的讨论

Josephson效应发现的历史回顾，相关量子理论精要，Josephson方程的推导，外加磁场对最大Josephson电流的影响等，在本文中进行了讨论。     

基于噪声的非线性特性研究

通过求解粒子在周期势场中布朗运动相应的Fokker-Planck方程,得到了超导Josephson结的非线性特性曲线,计算结果与实验符合很好.     

Fabrication and characteristics of intrinsic Josephson junctions in Bi<Subscript>2</Subscript>Sr<Subscript>2</Subscript>CaCu<Subscript>2</Subscript>O<Subscript>8+x</Subscript> single crystals

Mesa-structured intrinsic Jospehson junctions are fabricated in Bi2Sr2CaCu2O8 x single crystals.Typical current-voltage characteristics of intrinsic Josephson junctions are observed .which include multiple quasi-particle branches,surface junction with critical current lower than those of inner junctions.and subgap structures on quasi-particle branches,The corresponding physical explanations are also given .The energy gap voltage of the intrinsic Josephson junctions at 30 K is about 20mV Besides,The measured Ic-T relationship agrees quite well with the theoretical computations based on dx′-y′-wave superconductor.Our measured dI/dV-V relationship shows the V-shaped gap structure,obviously differing from the U-shaped gap structure of the s-wave superconductor.     

基于系统变量的线性变换实现对Josephson结电路的混沌控制

研究了Josephson电路系统的复杂动力学行为.首先建立了系统的动力学方程,通过分岔图和相平面图分析了系统从周期到混沌的过程,然后运用基于系统变量的线性变换实现了对Josephson结电路的控制.结果表明,通过改变系统变量之间的线性变换矩阵,可以实现对Josephson结电路混沌运动的控制.     

一个考虑耗散效应的玻色_爱因斯坦凝聚的双势阱的经典模型

在双势阱模型的基础上考虑了Josephson流与凝聚体的相互作用而引起的阻尼效应,及粒子之间的相互作用势能差而引起的保守力,及凝聚体耗散等因素,提出了一个经典模型,得出相对粒子数Z(t)的表达式,并分别讨论了Josephson振荡、自囚、阻尼摆、从自囚到Josephson振荡.     

不对称s波超导体/绝缘层/s波超导体结的直流Josephson电流

在不对称s波超导体/绝缘层/s波超导体Josephson结(s/I/s)中,考虑结界面粗糙散射情况下,运用Bogoliubov deGennes(BdG)方程和Furusaki Tsukada(FT)的电流公式计算准粒子的输运系数及s/I/s结的直流Josephson电流.研究表明,结界面的通常势垒和粗糙散射均抑制结中准粒子的Andreev反射,降低了流过s/I/s结的直流Josephson电流,直流Josephson电流I随温度T的变化关系与结两侧的对称性有关.     

f波超导体/绝缘层/f波超导体结中势垒散射对直流Josephson电流的影响

通过计算界面势垒散射强度对直流Josephson电流的影响,研究了f波超导体/绝缘层/f波超导体结的直流Josephson电流与温度T和结两侧晶轴方位角之间的关系.我们发现:f波超导体/绝缘层/f波超导体结界面的势垒强度总是抑制结中准粒子的Andreev反射,降低流过f波超导体/绝缘层/f波超导体结的直流Josephson电流.当结两边晶轴方位角相同时,Josephson电流的振荡周期是2π;特别地,当结两边晶轴方位角不同时,其振荡周期不再是2π,而是会随着势垒强度的增大,振荡周期变小.     

关于三维超导结的Josephson运动方程的研究

文中,三维超导结的Josephson运动方程被推导出来,并求出了它的解.     

物理所发现一新量子效应——光子约瑟夫森效应

[物理所]最近，中国科学院物理研究所／北京凝聚态物理国家实验室刘伍明研究组在光与物质相互作用领域取得重要进展。他们发现在包含冷原子的两个弱耦合微腔的光学系统中可以产生一种新颖的量子效应——光子约瑟夫森效应（Josephson effect of photons），并进一步设计了相干光子干涉器件。     

利用Fabry-Perot谐振腔和介质谐振天线实现约瑟夫森结阵列的自辐射

本文提出了一种利用Fabry-Perot谐振腔和介质谐振天线,同时集成偶极天线阵实现约瑟夫森结阵列自辐射的方法.在介质基片上制作集成偶极天线阵的双晶约瑟夫森结阵列,并将其嵌入到Fabry-Perot谐振腔内.将基片作为一介质谐振天线,使其与Fabry-Perot谐振腔谐振在同一频率下,从而通过高频电磁耦合机制实现结之间以及结与外部微波电路之间的耦合.文中分别进行了数值仿真和实验研究.对一个包含166个双晶约瑟夫森结的结阵列进行了液氮温度时的测试,在片外（off-chip）检测到了75.2GHz,10pW的辐射信号,与仿真结果吻合.该方法为基于约瑟夫森效应的太赫兹（THz）源提供了一种可能.     

Nb约瑟夫森结中AlO_x阻挡层阳极氧化的研究

用阳极氧化电压谱图技术分析Ｎｂ／ＡｌＯｘ／Ｎｂ约瑟夫森结中ＡｌＯ２隧道阻挡层（绝缘层）与Ｎｂ电极之间的介面特征并测量谱图阻挡层阳极氧化的电压宽度，发现这种电压宽度与阻挡层厚度密切相关．通过阻挡层阳极氧化电压宽度Ｖｗ和沉积Ａｌ厚Ｄ的关系测量，证实Ａｌ上ＡｌＯｘ的生长只取决于氧化条件而与沉积的Ａｌ层厚度无关．本文还提出了一种由Ｖｗ估算Ａｌ上生长的ＡｌＯｘ厚度的方法．实验证明，阳极氧化电压谱图技术是监测约瑟夫森结的介面特性和临介电流密度的有用工具，对高温超导结及其超导器件的开发起着重要的作用．     

约塞夫森“链”的理论处理

This paper extends DC and AC Josephson equations from a single Josephson junction to any number of junctions in the linear "chain" using G.L .phenomenological theory and B.C.S theory, i.e, it demonstrates theoretically that one Josephson "chain" can be treated as one single Josephson "junction".     

DSC系统的dc Josephson电流阶梯效应

由Ｊｏｓｅｐｈｏｓｎ关系，得出ＤＳＣ系统分别处于稳恒磁场和交变磁场时，两结间所加交变电压的直流分量改变，将导致系统的ｄｃ Ｊｏｓｅｐｈｓｏｎ电流产生多次阶梯效应。     

Tl2Ba2CaCu2O8高温超导薄膜中的本征约瑟夫森效应

我们在不同温度下对Ｔｌ２Ｂａ２ＣａＣｕ２Ｏ８高温超导薄膜进行了本征的瑟夫森效应研究，对薄膜微桥Ｉ－Ｖ特性和临界是流随温度变化关系的测试表明，Ｔｌ２Ｂａ２Ｃａ２Ｃｕ２Ｏ８薄膜中的本征约瑟夫森效应呈现ＳＩＳ结特性。     

Coherent transfer of Cooper pairs by a movable grain

Superconducting circuits that incorporate Josephson junctions are of considerable experimental and theoretical interest, particularly in the context of quantum computing. A nanometre-sized superconducting grain (commonly referred to as a Cooper-pair box) connected to a reservoir by a Josephson junction is an important example of such a system. Although the grain contains a large number of electrons, it has been experimentally demonstrated that its states are given by a superposition of only two charge states (differing by 2e, where e is the electronic charge). Coupling between charge transfer and mechanical motion in nanometre-sized structures has also received considerable attention. Here we demonstrate theoretically that a movable Cooper-pair box oscillating periodically between two remote superconducting electrodes can serve as a mediator of Josephson coupling, leading to coherent transfer of Cooper pairs between the electrodes. Both the magnitude and the direction of the resulting Josephson current can be controlled by externally applied electrostatic fields.     

SINIS结的电流-位相关系

本文以推广了的Jacobson方法在小电流的假设下导出了SINIS势阱结的电流-位相关系。在所谓临界厚度下它退化为通常的正弦函数关系,其临界电流对温度和结区厚度的依赖关系兼有了SIS和SNS结的某些重要性质。由于该结有较好的耦合能力,故可期望替代SNS结做某些实际应用。     

Acid etching process for fabrication of Bi2Sr2CaCu2O8＋x stack

We adopted a new method, acid etching process, to fabricate the intrinsic Josephson junctions based on the Bi2Sr2CaCu2O8 x single crystals. By soaking the crystals into the dilute hydrochloric acid, we fabricated a junction stack successfully, and meantime made the surrounding area insulated. A certain concentration of hydrochloric acid was used to maintain the roughness of the modified layer. The cur-rent-voltage characteristic was achieved through the four terminal measurement. We could control the junctions' number by changing the concentration and the soaking time. We also found that the thick-ness of the stack was equal to the average height of the insulation layer. Such a simple, convenient and controllable fabrication method with a high yield might widen the applications of the intrinsic Joseph-son junctions.