We consider a fractional Josephson vortex in an infinitely long 0-kappa Josephson junction. A uniform bias current applied to the junction exerts a Lorentz force acting on a vortex. When the bias current becomes equal to the critical (or depinning) current, the Lorentz force tears away an integer fluxon and the junction switches to the resistive state. In the presence of thermal and quantum fluctuations this escape process takes place with finite probability already at subcritical values of the bias current. We analyze the escape of a fractional vortex by mapping the Josephson phase dynamics to the dynamics of a single particle in a metastable potential and derive the effective parameters of this potential. This allows us to predict the behavior of the escape rate as a function of the topological charge of the vortex.
Breakdown of the escape dynamics in Josephson junctions
我们发现了高临界电流密度Jc的约瑟夫森结中零电压态的逃逸率的反常行为。在这项研究中，我们采用了YBa 2Cu 3 O 7-x晶界结，它跨越了广泛的Jc，并有适当的电动力学参数。这种高Jc结，当滞后时，不按照预期的随机约瑟夫森分布从超导切换到正常状态，尽管具有标准的约瑟夫森特性，例如夫琅和费磁场图案。开关电流分布（SCD）是一致的非平衡动力学发生在当地，而不是一个全球范围内。这意味着，宏观量子现象似乎是实际上无法实现的高Jc结。我们认为，SCD是一个准确的手段来衡量非平衡效应。这种从全局到局部动力学的转变与所有类型的弱连接都相关，包括纳米混合约瑟夫森结的新兴家族。因此，在使用这种结时应该谨慎，例如，寻找马约拉纳费米子。
Thermal fluctuations in moderately damped Josephson junctions: Multiple escape and retrapping, switching- and return-current distributions and hysteresis
Quantum and classical resonant escapes of a strongly-driven Josephson junction
本文研究了直流SQUID在25 mK（远低于量子-经典交叉温度$T_{cr}$）强共振交流驱动下的相位逃逸特性。SQUID包含两个Nb/Al-AlO $_{x} $ /Nb隧道结，其约瑟夫森电感远大于回路电感，因此其可被视为具有可调临界电流的单个结。我们发现，随着微波功率的增加$W$和在一定的频率$ν$和$ν$ /2，在开关电流分布，\textrm{which is the result of macroscopic quantum tunneling of the phase across the junction}的单一主峰，首先向低偏置电流$I$，然后共振峰的发展。这些结果解释了量子共振相位逃逸涉及单光子和双光子微波抑制势垒。随着$W$进一步增加，主峰逐渐消失，并且共振峰增长为单个共振峰，同时进一步向较低的$I$移动。在一定的$W$处，出现第二共振峰，根据$ν$的值，其可以位于非常低的$I$处。基于经典运动方程的分析表明，这种共振峰可能是由于非线性系统的分岔导致相位粒子以极大振幅共振逃逸而产生的。我们的实验结果和理论分析表明，在$T\ll T_{cr}$中，相粒子的逃逸可以由经典过程控制，如强交流驱动下非线性系统的动力学分岔。
Sensitive photon detection in the gigahertz band constitutes the cornerstone to study different phenomena in astronomy, such as radio burst sources, galaxy formation, cosmic microwave background, axions, comets, gigahertz-peaked spectrum radio sources and supermassive black holes. Nowadays, state of the art detectors for astrophysics are mainly based on transition edge sensors and kinetic inductance detectors. Overall, most sensible nanobolometers so far are superconducting detectors showing a noise equivalent power (NEP) as low as 2x10-20 W/Hz1/2. Yet, fast thermometry at the nanoscale was de…
We present a study of the first and second switches (SWs) with nearly identical switching current $I_{\rm SW}$ in Bi$_2$Sr$_2$Ca$_{0.85}$Y$_{0.15}$Cu$_2$O$_y$ intrinsic Josephson junctions (IJJs). In contrast to early studies where a large difference between $I_{\rm SW}^{\rm 1st}$ and $I_{\rm SW}^{\rm 2nd}$ was observed, a crossover temperature $T_{\rm cr}$ to the quantum phase escapes for the 2nd SW is strongly reduced $(\sim$2.8~K) and agrees with that for the 1st SW. This confirms that the anomalous enhancement of $T_{\rm cr}^{\rm 2nd}$, commonly observed in the IJJs with $I_{\rm SW}^{\rm 1…
Switching Current Measurements of EuBa2Cu3Oy Intrinsic Josephson Junctions
研究了两种不同各向异性参数γ（=（m*c/m*ab）1/2）的EuBa 2 Cu 3 O y（Eu 123）本征约瑟夫森结（IJJs）的开关动力学.与Bi 2212中的弱耦合IJJ相比，由于Eu 123 IJJ的强耦合性质，在它们的开关电流分布P（I）中观察到了与单堆约瑟夫森结的热激活逃逸模型的显著偏离。这表明在高温液态He中观察到宏观量子隧穿。
Enhanced Macroscopic Quantum Tunneling in Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ Intrinsic Josephson Junction Stacks
我们用微波辐射研究了Bi $_2$ Sr $_2$ CaCu $_2$ O $_{8+δ}$本征约瑟夫森结在毫开尔文温度下的宏观量子隧穿.测量结果表明，均匀切换N结堆的逃逸率是约$N^2$倍高于具有相同的等离子体频率的单个结。我们认为，这种巨大的增强堆栈中的宏观量子隧穿率是由电流的波动，发生在由环境的阻抗加载的结的串联阵列。
Experiments on the distributions of switching currents in Josephson junctions are sensitive probes of the mechanism by which a junction changes abruptly to a finite voltage state. At low temperatures data exhibit smooth and gradual deviations from the expectations of the classical theory of thermal activation over the barrier in the tilted washboard potential. In this paper it is shown that if a very small proportion of the noise energy entering the apparatus at room temperature survives filtering and reaches the sample, it can enhance the escape rate sufficiently to replicate experimental obs…
Multi-Junction Switching in Bi$_2$Sr$_{1.6}$La$_{0.4}$CuO$_{6+δ}$ Intrinsic Josephson Junctions
研究了多结开关（MJS）的动力学：阵列中的多个本征约瑟夫森结（IJJ）同时切换到有限电压状态。通过改变串联连接到Bi $_2$ Sr $_{1.6}$ La $_{0.4}$ CuO $_{6+δ}$ IJJ阵列的负载电阻，成功地调谐了多开关结（$N$）的数量。宏观量子隧穿机制中$N$的逃逸率的独立性表明MJS是一个$successive$开关过程而不是$collective$过程。MJS的起源解释的负载曲线的梯度和准粒子分支的开关电流在电流-电压平面的相对幅度。
Josephson junctions and superconducting wires when probed with current pulses exhibit stochastic switching from superconducting to a stable non-zero voltage state. Electrical current dependence of the switching probability (so called S-curve) or switching current distribution is a fingerprint of the physics governing the escape process. This work addresses the criterion of independent switching event in a series of switching experiments. Treating Josephson junction as an electrical coin with current-tuned switching probability we investigate effect of correlation between switching events on th…
A survey of classical and quantum interpretations of experiments on Josephson junctions at very low temperatures
在1968年引入后的几十年里，电阻和电容分流结（RCSJ）模型，有时也被称为斯图尔特-麦克伯模型，被成功地应用于研究嵌入各种超导电路中的约瑟夫森结的动力学。1980年，A. J. Leggett的一个理论猜想提出了约瑟夫森结在非常低的温度下可能出现的一种新的、完全不同的行为。许多实验似乎证实了这一预测，很快人们就认为，几十毫开尔文的结应该被视为宏观量子实体。因此，它们将在其有效势阱中拥有离散能级，并且将通过宏观量子隧穿过程从这些阱中逃逸（出现有限结电压）。追求这种新物理的热情导致了在这种低温状态下实际上放弃了RCSJ模型。在本文中，我们考虑选择的基本上是原型的实验，进行了确认预期的宏观量子行为方面的意图在约瑟夫森结。我们提出两个问题：（1）非量子理论（RCSJ模型）在复制这些实验方面有多成功？(2)这些实验的数据确实反映了宏观量子行为的证据有多强？
Analysis of Josephson junctions switching time distributions for the detection of single microwave photons
Università di Salerno（萨莱诺大学）；INFN, Gruppo Collegato Salerno（意大利国家核物理研究所萨莱诺协作组）；INFN, Laboratori Nazionali di Frascati（意大利国家核物理研究所弗拉斯卡蒂国家实验室）；University of Roma Tre（罗马第三大学）；Univ. of Sannio（桑尼奥大学）
