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arXiv 1407.8480cond-mat.dis-nncond-mat.mes-hallquant-ph
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多体局域相运动局部积分的构造

Constructing local integrals of motion in the many-body localized phase

Anushya Chandran, Isaac H. Kim, Guifre Vidal, Dmitry A. Abanin

摘要:

多体局域化提供了量子系统中遍历性破缺的一般机制。与传统的遍历系统相比,多体局域化(MBL)系统的特点是大量的局部运动积分(LIOM),这是这些系统中没有输运和热化的基础。在这里,我们报告一个物理动机的建设的局部积分的运动在MBL阶段。我们表明,任何本地运营商(例如,局部粒子数或自旋翻转算子),与系统的哈密顿量一起演化并随时间平均,变成MBL相中的LIOM。这种算子具有明确的物理意义,描述了MBL系统对局部扰动的响应。特别地,当局部算子表示某些全局守恒量的密度时,相应的LIOM描述了该守恒量如何通过MBL相传播。这些LIOM具有独特的定义和实验可测量性,为在实验和数值模拟中表征MBL相的性质提供了一种天然的工具。我们证明了后者通过数值构建一个广泛的一组LIOMs在MBL阶段的无序自旋链模型。我们表明,由此产生的LIOMs是准本地的,并使用它们的衰减提取本地化长度和建立的MBL和遍历阶段之间的过渡的位置。

英文摘要:

Many-body localization provides a generic mechanism of ergodicity breaking in quantum systems. In contrast to conventional ergodic systems, many-body localized (MBL) systems are characterized by extensively many local integrals of motion (LIOM), which underlie the absence of transport and thermalization in these systems. Here we report a physically motivated construction of local integrals of motion in the MBL phase. We show that any local operator (e.g., a local particle number or a spin flip operator), evolved with the system's Hamiltonian and averaged over time, becomes a LIOM in the MBL phase. Such operators have a clear physical meaning, describing the response of the MBL system to a local perturbation. In particular, when a local operator represents a density of some globally conserved quantity, the corresponding LIOM describes how this conserved quantity propagates through the MBL phase. Being uniquely defined and experimentally measurable, these LIOMs provide a natural tool for characterizing the properties of the MBL phase, both in experiments and numerical simulations. We demonstrate the latter by numerically constructing an extensive set of LIOMs in the MBL phase of a disordered spin chain model. We show that the resulting LIOMs are quasi-local, and use their decay to extract the localization length and establish the location of the transition between the MBL and ergodic phases.

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