Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, 6020 Innsbruck, Austria and Institute for Theoretical Physics, University of Innsbruck, 6020 Innsbruck, Austria.
Institut für Theoretische Physik, Technische Universität Dresden, 01062 Dresden, Germany.
Phys Rev Lett. 2014 Oct 31;113(18):180601. doi: 10.1103/PhysRevLett.113.180601. Epub 2014 Oct 29.
One necessary criterion for the thermalization of a nonequilibrium quantum many-particle system is ergodicity. It is, however, not sufficient in cases where the asymptotic long-time state lies in a symmetry-broken phase but the initial state of nonequilibrium time evolution is fully symmetric with respect to this symmetry. In equilibrium, one particular symmetry-broken state is chosen as a result of an infinitesimal symmetry-breaking perturbation. From a dynamical point of view the question is: Can such an infinitesimal perturbation be sufficient for the system to establish a nonvanishing order during quantum real-time evolution? We study this question analytically for a minimal model system that can be associated with symmetry breaking, the ferromagnetic Kondo model. We show that after a quantum quench from a completely symmetric state the system is able to break its symmetry dynamically and discuss how these features can be observed experimentally.
对于非平衡量子多粒子系统的热化，一个必要的条件是遍历性。然而，在渐近长时间状态处于对称破缺相而非平衡时间演化的初始状态完全对称于该对称的情况下，这是不够的。在平衡态中，由于微小的对称破缺微扰，选择了一个特定的对称破缺状态。从动力学的角度来看，问题是：这种微小的微扰是否足以使系统在量子实时演化过程中建立非零的有序性？我们对一个与对称破缺有关的最小模型系统进行了分析研究，该模型系统是铁磁 Kondo 模型。我们表明，在从完全对称的状态进行量子淬火后，系统能够动态地打破其对称性，并讨论如何在实验中观察到这些特征。
