约瑟夫森结跳变电流在微波辐照下的分布

在16 mK的极低温下,我们对电流偏置的Nb/AlOx/Nb结进行了跳变电流统计分布的测量.在没有外加微波的辐照时,分布曲线只有一个峰;在有外加微波的辐照时,其跳变电流的统计分布除了基峰外,会出现谐振峰,形成双峰结构.该谐振峰的位置和结的量子化的能级相关,其高度随外加微波功率的改变而改变.研究约瑟夫森结跳变电流在微波辐照下的分布,对于研究超导量子比特的能级量子化、Rabi振荡等具有重要的意义.     

Josephson结跳变电流在不同温度下的统计分布

本工作提出了一种通过对时间的测量来获得单个Josephson结的跳变电流统计分布P(I)的电路,该电路具有很好的精度和速度.利用该电路我们首次从4.2K到30mK的不同温度下,对NbN/AlN/AbN结和Nb/AlOx/Nb结的跳变电流统计分布进行了测量,得到了一系列P(I).在一定的温度范围内,P(I)和理论值符合的很好.该电路结合其他的实验手段,将在今后研究Josephson结其他物理性质(例如Rabi振荡)中发挥很好的作用.     

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．     

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.     

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Tc SQUID）;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Tc SQUID.文章主要是对高Tc SQUID中所使用的高温超导约瑟夫森结进行评述.     

基于高温超导本征约瑟夫森效应的新型两端恒流器件

我们利用高温超导本征约瑟夫森效应,研制了一种超导薄膜两端恒流器件.恒流器件是将生长在斜切20度LaAlO3基片上的Tl-2212超导薄膜光刻成微桥得到的.对于6μm×8μm的微桥器件,其最高工作电压可达15V以上,当两端电压在1V～11V之间变化时,电流基本稳定在4.3mA,误差不超过±5%,动态内阻大于104 Ω,在最佳工作位置(3V～8V)动态内阻可以达到105 Ω.通过数字模拟,对实际应用中两端恒流器件的rf调制进行了较详细的分析,并可使恒定电流上rf调制小于1%.     

外场与介观约瑟夫森结相互作用的不变本征算符法研究

本文首先详细介绍了场与介观约瑟夫森结相互作用系统的哈密顿量,进一步讨论了系统的量子化方案,然后简要介绍了不变本征算符法及其基本应用.在此基础上,用不变本征算符法求得外场与介观约瑟夫森结相互作用系统的能级间隔.     

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。     

基于约瑟夫森器件的超导量子比特

超导量子比特利用了超导约瑟夫森隧道结的非线性效应,采用了半导体集成电路的工艺,以其无能耗,大设计加工自由度,易规模化等优点而倍受注目。本文对超导量子比特的基本原理及发展过程作了简要综述。首先简要回顾了量子计算的历史,然后介绍了超导量子比特的设计及其调控,并对各种超导量子比特的消相干进行了讨论。     

外场中超导结的直流约瑟夫逊电流的计算

外加磁场对超导体/半导体/超导体结的临界电流有一定影响。超导结的临界电流与磁场的曲线非常类似于单色光在单狭缝衍射的夫琅和费图样。该文在未考虑外加磁场的超导体/半导体/超导体结的临界电流的基础上,进一步对外加磁场的情形进行了研究,并对其结果借助M athem atica软件做了进一步的讨论。     

Fluctuation power spectrum of a Josephson junction

The fluctuation power spectrum of the Josephson junction has been evaluated in the limit of large energy barriers [(U _n ^max−U _n ^min)γ]≫1 and small currents [x≪x _e]. The result is valid for finite capacitance of the junction. The effect of the fluctuating Josephson current on the voltageV(t) across the junction has also been taken into account.     

Anisotropy of p-wave Josephson junction

<正>The anisotropy of the dc Josephson current in the superconducting junctions of the p-wave equal spin pairing symmetry is theoretically investigated by the Furusaki-Tsukada-like formula.The current phase relations exhibit different oscillation periods and different phase shifts for the current along different directions,respectively.     

Josephson current in an irradiated Weyl semimetal junction

The influence of the off-resonant circularly polarized light on the Josephson current in the time-reversal broken superconducting Weyl semimetal junctions is investigated by using the Bogoliubov–de Gennes equation and the transfer matrix approach. Both the zero momentum BCS pairing states and the finite momentum Fulde–Ferrell–Larkin–Ovchinnikov(FFLO) pairing states are considered for the Weyl superconductors. When a circularly polarized light is applied, it is shown that the current phase relation remains unchanged for the BCS pairing with the increasing of incident radiation intensity A_0. For FFLO pairing, the Josephson current exhibits the 0–π transition and periodic oscillation as a function of A_0. The dependence of free energy and critical current on A_0 are also investigated.     

Interfacial spin Hall current in a Josephson junction with Rashba spin—orbit coupling

We theoretically investigate the spin transport properties of the Cooper pairs in a conventional Josephson junction with Rashba spin-orbit coupling considered in one of the superconducting leads.It is found that an angle-resolved spin supercurrent flows through the junction and a nonzero interfacial spin Hall current driven by the superconducting phase difference also appears at the interface.The physical origin of this is that the Rashba spin-orbit coupling can induce a triplet order parameter in the s-wave superconductor.The interfacial spin Hall current dependences on the system parameters are also discussed.     

用Josephson结电子模拟器测量磁通量子2e/h

介绍用Josephson结电子模拟器在政党温度下，模拟测量磁通量子2e/h，用模拟器来研究Josephosn结的特性。该实验可作为普通物理实验中课题设计实验的一个内容。     

Quantum transitions of a small Josephson junction array

We have experimentally studied a small Josephson junction array in the presence of microwave irradiation. The array has comparable energy scales for single-charge effects and the Josephson effect, resulting in a discrete set of macroscopic eigenenergy levels. Excitation of the array by low-power microwaves is possible at frequencies where the photon energy matches the level spacing. The microwave frequency and amplitude dependence show that the excitation mechanism involves resonant quantum coherent dynamics of the array.     

Relaxation dynamics in a stochastic bosonic Josephson junction

We consider a bosonic Josephson junction in the Bose-Hubbard two-mode approximation where some of the parameters are corrupted by physically meaningful noise processes and study the corresponding relaxation dynamics towards its equilibrium state. We show with numerical simulations that this model can essentially capture all the important features observed in a recent experiment regarding the relaxation dynamics in one-dimensional bosonic Josephson junctions, namely the damped oscillations of the population imbalance and the relative phase, as well as the large final coherence factor. We expect that this work will further motivate research about the origin of relaxation mechanism in these systems.     

Reduced quantum fluctuation in mesoscopic Josephson junction with nonclassical radiation field at finite temperature

We have investigated the reduced fluctuation properties in a mesoscopic Josephson junction with the squeezed state at a finite temperature. It is shown that the fluctuations increase with increasing temperature and the mesoscopic Josephson junction subsystem can exhibit squeezing behaviour at an appropriately low temperature.