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arXiv 1506.06754cond-mat.str-elmath-phmath.MPquant-ph
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对称性分裂与扭曲缺陷

Symmetry fractionalization and twist defects

Nicolas Tarantino, Netanel H. Lindner, Lukasz Fidkowski

摘要:

二维的拓扑序可以用去限制的准粒子激发--任意子--和它们的编织统计来描述。然而,最近人们意识到,这些数据并不能完全描述存在未破缺的全局对称性的情况。在这种情况下,可以有多个不同的量子相位,具有相同的任意子和统计,但具有不同的对称性分数化模式-称为对称性丰富拓扑(SET)序。当整体对称群$G$(我们认为它是离散的)不改变拓扑超选择扇区时--也就是说,不把一种类型的任意子变成另一种类型的任意子--我们可以想象$G$在每个任意子周围的作用的局部版本。这导致了投影表示和对称分解的群上同调描述,其中$H^2(G,{\cal A})$是相关群。本文讨论对称群$G$可能置换任意子类型的一般情形。我们发现,尽管缺乏一个本地行动的$G$,人们仍然可以理解所谓的扭曲群上同调描述的对称性分解,并显示如何将此数据编码在融合规则的关联性的外在“扭曲”缺陷的对称性。此外,在Hermele工作的基础上,我们构造了一类广泛的精确求解的模型,这些模型表现出这种扭曲的对称性分解,并将它们连接到我们的正式框架中。

英文摘要:

Topological order in two dimensions can be described in terms of deconfined quasiparticle excitations - anyons - and their braiding statistics. However, it has recently been realized that this data does not completely describe the situation in the presence of an unbroken global symmetry. In this case, there can be multiple distinct quantum phases with the same anyons and statistics, but with different patterns of symmetry fractionalization - termed symmetry enriched topological (SET) order. When the global symmetry group $G$, which we take to be discrete, does not change topological superselection sectors - i.e. does not change one type of anyon into a different type of anyon - one can imagine a local version of the action of $G$ around each anyon. This leads to projective representations and a group cohomology description of symmetry fractionalization, with $H^2(G,{\cal A})$ being the relevant group. In this paper, we treat the general case of a symmetry group $G$ possibly permuting anyon types. We show that despite the lack of a local action of $G$, one can still make sense of a so-called twisted group cohomology description of symmetry fractionalization, and show how this data is encoded in the associativity of fusion rules of the extrinsic `twist' defects of the symmetry. Furthermore, building on work of Hermele, we construct a wide class of exactly solved models which exhibit this twisted symmetry fractionalization, and connect them to our formal framework.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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