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arXiv 1502.02592quant-phcond-mat.othermath-phmath.MP
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一维量子行走的体边对应

Bulk-edge correspondence of one-dimensional quantum walks

C. Cedzich, F. A. Grünbaum, C. Stahl, L. Velázquez, A. H. Werner, R. F. Werner

摘要:

我们概述了一维量子行走的对称性保护拓扑相理论。我们假设谱间隙围绕着可区分的点+1和-1,其中只允许离散的特征值。通过整数或二进制索引的相位分类扩展了平移不变系统在其能带结构方面的已知分类。然而,我们的理论不需要任何平移不变性,并且我们在这个一般设置中定义的指数在任意对称局部扰动下是不变的,即使是那些不能连续收缩到恒等式的扰动。更准确地说,我们为每次行走定义了两个指数,分别表征了远离右侧和远离左侧的行为。它们的和是+1和-1处本征态数目的下界。对于平移不变系统,索引之和为零,因此其中之一已经表征了相位。通过连接两个具有不同指数的体相,我们得到了一个行走,其中右指数和左指数不再抵消,因此理论预测束缚态为+1或-1。这是一个严格的声明体边缘对应。结果也适用于哈密顿的情况下,一个单一的间隙为零。

英文摘要:

We outline a theory of symmetry protected topological phases of one-dimensional quantum walks. We assume spectral gaps around the symmetry-distinguished points +1 and -1, in which only discrete eigenvalues are allowed. The phase classification by integer or binary indices extends the classification known for translation invariant systems in terms of their band structure. However, our theory requires no translation invariance whatsoever, and the indices we define in this general setting are invariant under arbitrary symmetric local perturbations, even those that cannot be continuously contracted to the identity. More precisely we define two indices for every walk, characterizing the behavior far to the right and far to the left, respectively. Their sum is a lower bound on the number of eigenstates at +1 and -1. For a translation invariant system the indices add up to zero, so one of them already characterizes the phase. By joining two bulk phases with different indices we get a walk in which the right and left indices no longer cancel, so the theory predicts bound states at +1 or -1. This is a rigorous statement of bulk-edge correspondence. The results also apply to the Hamiltonian case with a single gap at zero.

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