Marcuzzi Matteo, Buchhold Michael, Diehl Sebastian, Lesanovsky Igor
School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom.
Institut für Theoretische Physik, Universität zu Köln, D-50937 Cologne, Germany.
Phys Rev Lett. 2016 Jun 17;116(24):245701. doi: 10.1103/PhysRevLett.116.245701.
Stochastic processes with absorbing states feature examples of nonequilibrium universal phenomena. While the classical regime has been thoroughly investigated in the past, relatively little is known about the behavior of these nonequilibrium systems in the presence of quantum fluctuations. Here, we theoretically address such a scenario in an open quantum spin model which, in its classical limit, undergoes a directed percolation phase transition. By mapping the problem to a nonequilibrium field theory, we show that the introduction of quantum fluctuations stemming from coherent, rather than statistical, spin flips alters the nature of the transition such that it becomes first order. In the intermediate regime, where classical and quantum dynamics compete on equal terms, we highlight the presence of a bicritical point with universal features different from the directed percolation class in a low dimension. We finally propose how this physics could be explored within gases of interacting atoms excited to Rydberg states.
具有吸收态的随机过程是非平衡普遍现象的实例。虽然经典情况在过去已得到充分研究，但对于这些非平衡系统在量子涨落存在时的行为却知之甚少。在此，我们从理论上研究了一个开放量子自旋模型中的这种情况，该模型在其经典极限下会经历定向渗流相变。通过将问题映射到一个非平衡场论，我们表明，由相干而非统计的自旋翻转引起的量子涨落的引入改变了相变的性质，使其变为一阶相变。在经典和量子动力学平等竞争的中间区域，我们突出了一个双临界点的存在，其具有与低维定向渗流类不同的普遍特征。我们最终提出了如何在被激发到里德堡态的相互作用原子气体中探索这种物理现象。
