标题： 小电容约瑟夫森结的线索：并联的库珀对理想导体和欧姆电阻会带来什么？ 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： 通过使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亚能隙和分流电阻共同作用对小电容约瑟夫森结的影响。 通过在两种偏置方案存在的情况下使用线性响应理论，我们证明了在该领域早期论文中预见的理想导电性并不稳健，既不抵抗量子相位涨落，也不抵抗耗散效应。 通过将两者都包含在哈密顿量中，我们证明了欧姆耗散强度的增加会在热力学平衡中引发贝雷津斯基-科斯特里茨-索利斯量子相变。 随后，我们在线性响应理论框架下研究了热力学平衡状态下的电荷和相位涨落。 我们发现，在量子约瑟夫森结中，相位粒子的运动不会从扩散变为局域化，因此不会导致绝缘体-超导体转变，这与通常的观点不同。 在相变点，我们证明了：i）相位粒子的运动从弹道式变为局域化；ii）通过开启与环境的耦合，在电荷响应函数中出现一个寿命较长的有限频率激发：它首先演化为共振，然后在相变时消失。 我们研究了线性响应之外的后果，得出了对该系统的一种替代的全面物理图像：我们预测了一个耗散准粒子电流向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.