论文标题
非平衡对称性保护拓扑顺序：半局部吉布斯合奏的出现
Nonequilibrium symmetry-protected topological order: emergence of semilocal Gibbs ensembles
论文作者
论文摘要
我们考虑全局淬火后量子自旋链中的非平衡时间演变。通常，一个非量子量子多体系统在本地放松到（广义的）Gibbs合奏，由具有准密度的保守算子建造。在这里，我们展示了当地哈密顿量的明确例子，这些汉密尔顿当地的保存定律的密度不是准局部性的，而是在发生时间进化的对称限制空间中这样的作用。由于它们，在无限时间出现的固定状态可以表现出非凡的特征。我们专注于一个带有自旋对称性的特定示例，这是以$ 1/2 $链条遇到的最常见的全局对称性。在特殊属性中，我们发现，在后期，由局部扰动在初始状态中触发的自旋块的熵过量会随着子系统的长度而对数增长。我们在零温度下以平衡状态建立了与对称性保护的拓扑顺序的联系，并研究了初始状态的（对称性）旋转或温度升高所诱导的顺序熔化。
We consider nonequilibrium time evolution in quantum spin chains after a global quench. Usually a nonequilibium quantum many-body system locally relaxes to a (generalised) Gibbs ensemble built from conserved operators with quasilocal densities. Here we exhibit explicit examples of local Hamiltonians that possess conservation laws with densities that are not quasilocal but act as such in the symmetry-restricted space where time evolution occurs. Because of them, the stationary state emerging at infinite time can exhibit exceptional features. We focus on a specific example with a spin-flip symmetry, which is the commonest global symmetry encountered in spin-$1/2$ chains. Among the exceptional properties, we find that, at late times, the excess of entropy of a spin block triggered by a local perturbation in the initial state grows logarithmically with the subsystem's length. We establish a connection with symmetry-protected topological order in equilibrium at zero temperature and study the melting of the order induced either by a (symmetry-breaking) rotation of the initial state or by an increase of the temperature.
