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arXiv 1609.02432quant-phcond-mat.quant-gascond-mat.str-el
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量子多体系统中混合态的拓扑序

Topological order of mixed states in quantum many-body systems

Fabian Grusdt

摘要:

拓扑序已成为区分相互作用多体系统基态的一种新的范式,而不需要传统的长程序。在这里,我们讨论这个概念的可能扩展到密度矩阵描述统计系综。对于一个大类的准热态,这可以实现为一些准局部哈密顿的热态,我们推广早期的密度矩阵拓扑的定义,一般的多体系统具有强关联。我们指出,拓扑秩序的鲁棒性,定义为一种模式的远程纠缠,关键取决于所考虑的扰动。虽然在一个无限封闭的量子系统中,它在本质上受到保护,不受任意强度的局部扰动的影响,但如果耦合足够强,纯粹的局部扰动可以破坏耦合到浴池的开放系统的拓扑秩序。我们讨论了有限温度量子霍尔态的分类方案,指出经典的霍尔效应可以理解为一个有限温度的拓扑相位。

英文摘要:

Topological order has become a new paradigm to distinguish ground states of interacting many-body systems without conventional long-range order. Here we discuss possible extensions of this concept to density matrices describing statistical ensembles. For a large class of quasi-thermal states, which can be realized as thermal states of some quasi-local Hamiltonian, we generalize earlier definitions of density matrix topology to generic many-body systems with strong correlations. We point out that the robustness of topological order, defined as a pattern of long-range entanglement, depends crucially on the perturbations under consideration. While it is intrinsically protected against local perturbations of arbitrary strength in an infinite closed quantum system, purely local perturbations can destroy topological order in open systems coupled to baths if the coupling is sufficiently strong. We discuss our classification scheme using the finite-temperature quantum Hall states and point out that the classical Hall effect can be understood as a finite temperature topological phase.

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