We study a generic problem of dissipative quantum mechanics, a small local quantum system with discrete states coupled in an arbitrary way (i.e. not necessarily linear) to several infinitely large particle or heat reservoirs. For both bosonic or fermionic reservoirs we develop a quantum field-theoretical diagrammatic formulation in Liouville space by expanding systematically in the reservoir-system coupling and integrating out the reservoir degrees of freedom. As a result we obtain a kinetic equation for the reduced density matrix of the quantum system. Based on this formalism, we present a formally exact perturbative renormalization group (RG) method from which the kernel of this kinetic equation can be calculated. It is demonstrated how the nonequilibrium stationary state (induced by several reservoirs kept at different chemical potentials or temperatures), arbitrary observables such as the transport current, and the time evolution into the stationary state can be calculated. Most importantly, we show how RG equations for the relaxation and dephasing rates can be derived and how they cut off generically the RG flow of the vertices. The method is based on a previously derived real-time RG technique but formulated here in Laplace space and generalized to arbitrary reservoir-system couplings. Furthermore, for fermionic reservoirs with flat density of states, we make use of a recently introduced cutoff scheme on the imaginary frequency axis which has several technical advantages. We demonstrate the method by applying it to the nonequilibrium isotropic Kondo model in 1-loop. We present a systematic way to solve the RG equations analytically in the weak-coupling limit and provide an outlook of the applicability to the strong-coupling case.
Nonequilibrium finite-frequency noise of a resonance-level quantum dot close to a dissipative quantum phase transition: Functional Renormalization Group approaches
计算了非平衡共振能级量子点在弱耗散的离域相和强耗散的定域相之间的Kosterlitz-lesser（KT）型耗散量子相变附近的有限频率电流噪声.共振能级耦合到两个无自旋的费米子浴与有限的偏置电压和欧姆玻色子浴代表耗散环境。该系统等价于一个有效的各向异性Kondo模型。为了计算有限频率噪声，我们结合了两个最近发展的泛函重整化群（FRG）方法，在参考文献。[17，22]和参考文献。[23]第10段。在零温度和有限的频率的非平衡电流噪声示出了一个奇异的下降，在离域相位的频率等于偏置电压的幅度，而下降被涂抹的系统移动到本地化的阶段。对应的峰谷交叉被发现在交流电导的频率等于偏置电压的幅度。我们的实验结果和分数量子霍尔边缘（Fractional Quantum Hall Edge）状态和手征Luttinger液体之间的隧道的相关性和应用进行了讨论。
Nonequilibrium transport through an interacting monitored quantum dot
Institute of Theoretical and Computational Physics, Graz University of Technology（格拉茨工业大学理论与计算物理研究所）；JEIP, UAR 3573 CNRS, Collège de France, PSL Research University（法国国家科学研究中心联合研究单位3573 JEIP，法兰西学院，巴黎文理研究大学）
Observation of a dissipative phase transition in a one-dimensional circuit QED lattice
凝聚态物理在基于对称性和拓扑学的平衡相变的研究和理解方面的重大实验和理论进展推动了它的发展。然而，非平衡相变仍然是一个挑战，部分原因是它们在理论描述中的复杂性和系统地控制系统脱离平衡的额外实验困难。在这里，我们研究了一个一维链的72个微波腔，每个耦合到一个超导量子比特，并相干驱动系统进入一个非平衡稳态。我们发现了实验证据的耗散相变的系统中，其中的稳定状态的变化显着的平均光子数的增加。在两个观察到的相位之间的边界附近，系统表现出双稳态，特征切换时间长达60 ms -远远长于系统已知的任何固有速率。该实验展示了电路QED系统研究非平衡凝聚态物理的能力，并为未来用多体量子光学探索非平衡物理的实验铺平了道路。
Nonequilibrium processes from Generalised Langevin Equations: realistic nanoscale systems connected to two thermal baths
我们扩展了广义朗之万方程（GLE）方法[Phys. Rev. B 89，134303（2014）]，以模拟连接到两个不同温度下的两个实际热浴的中心经典区域。在这种非平衡条件下，通过中央系统在两个浴之间建立热流。的GLE-2B（GLE两浴）计划允许我们有一个现实的描述耗散中央系统及其周围的浴室。根据原来的GLE方法，扩展的Langevin动力学方案进行修改，以考虑到两套辅助自由度对应的映射的振动特性的每个浴。这些辅助变量，然后用来解决中心区域的非马尔可夫耗散动力学。由此产生的算法是用来研究一个模型的短铝纳米线连接到两个浴。使用GLE-2B方法的模拟结果进行比较，使用标准的恒温方法（基于马尔可夫朗之万和鼻子胡佛恒温器）进行的其他模拟的结果。我们专注于稳态制度和研究建立一个本地的温度分布系统内。获得一个平坦的轮廓或温度梯度的条件进行了详细的检查，在协议与早期的研究。结果表明，GLE-2B的方法是能够处理，在一个单一的计划，两个广泛不同的热传输制度，即弹道系统，没有温度梯度，和扩散系统的温度梯度。
