标题： 小电容约瑟夫森结的线索：从库珀对理想导体和并联欧姆电阻中能期待什么？ 显示英文标题

标题： A Clue on Small-Capacitance Josephson Junction: What to Expect from Cooper Pair Ideal Conductor and Ohmic Resistor in Parallel?

摘要： 利用解析方法和世界线蒙特卡罗方法，我们研究了量子相位涨落与准粒子次能隙以及旁路电阻共同作用在一个小电容约瑟夫森结上所引起的效应。 通过使用存在两种偏置方案时的线性响应理论，我们证明了在这一主题的开创性论文中预见的理想导电性并不稳健，无法抵抗量子相位涨落或耗散效应。 在哈密顿量中同时包含两者后，我们证明了增加欧姆耗散强度会在热力学平衡下引发一个 Berezinskii-Kosterlitz-Thouless量子相变。 然后我们利用线性响应理论研究了热力学平衡下的电荷和相位涨落。 我们发现，在量子约瑟夫森结中，相位粒子的运动并没有从扩散变为局域化，从而导致绝缘体-超导体转变，这与普遍认为的情况相反。 在转变点处，我们证明了：i）相位粒子的运动从弹道转变为局域化；ii）通过开启与环境的耦合，在电荷响应函数中会出现一个长寿命的有限频率激发：它首先演变成共振，然后在转变时消失。 非线性响应范围内的后果也被探讨，从而为该系统提供了另一种全面的物理图景：我们预测了一个从耗散准粒子电流到极化子库珀对电流的转变。 显示英文摘要

摘要： By using analytical and Worldline Monte Carlo approaches, we investigate the effects induced by quantum phase fluctuations combined with quasiparticle subgap and shunt resistances on a small-capacitance Josephson junction. By using the linear response theory in the presence of two biasing schemes, we prove that the ideal conduction, foreseen in the pioneering papers on this topic, is not robust against either quantum phase fluctuations or dissipative effects. By including both of them in the Hamiltonian, we prove that an increase of the Ohmic dissipation strength induces a Berezinskii-Kosterlitz-Thouless quantum phase transition in thermodynamic equilibrium. Then we study charge and phase fluctuations at the thermodynamic equilibrium within the linear response theory. We find that the phase particle motion, in a quantum Josephson junction, does not change from diffusive to localized, resulting in an insulator-superconductor transition, as is commonly believed. At the transition, we prove that: i) the motion of the phase particle changes from ballistic to localized; ii) by turning on the coupling with the environment, a long-lived excitation at finite frequency emerges in the charge response function: it evolves first into a resonance and then disappears at the transition. Consequences beyond the linear response regime are investigated, leading to an alternative comprehensive physical picture for this system: we predict a transition from a dissipative quasiparticle current to a polaronic Cooper pair current.