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arXiv 2007.15070cond-mat.stat-mechhep-th
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本征态热化假设超出标准指标:小频率下随机矩阵行为的出现

Eigenstate thermalization hypothesis beyond standard indicators: Emergence of random-matrix behavior at small frequencies

Jonas Richter, Anatoly Dymarsky, Robin Steinigeweg, Jochen Gemmer

摘要:

利用数值精确对角化方法,我们研究了两个不同的不可积量子自旋链的本征基中局域自旋算符的矩阵元。我们的重点是在什么程度上本地运营商可以表示为随机矩阵的问题,特别是在什么程度上矩阵元素可以被认为是不相关的。作为主要结果,我们表明,在一个固定的能量密度带子矩阵的特征值分布是一个敏感的探针之间的矩阵元素的相关性。我们发现,在尺度上的矩阵元素是在一个很好的协议与本征态热化假设的所有标准指标,本征值分布仍然表现出明确的签名的原始运营商,这意味着矩阵元素之间的相关性。此外,我们表明,在更小的能量尺度,本征值分布近似假设普遍的半圆形,表示过渡到随机矩阵的行为,特别是矩阵元素变得不相关。

英文摘要:

Using numerical exact diagonalization, we study matrix elements of a local spin operator in the eigenbasis of two different nonintegrable quantum spin chains. Our emphasis is on the question to what extent local operators can be represented as random matrices and, in particular, to what extent matrix elements can be considered as uncorrelated. As a main result, we show that the eigenvalue distribution of band submatrices at a fixed energy density is a sensitive probe of the correlations between matrix elements. We find that, on the scales where the matrix elements are in a good agreement with all standard indicators of the eigenstate thermalization hypothesis, the eigenvalue distribution still exhibits clear signatures of the original operator, implying correlations between matrix elements. Moreover, we demonstrate that at much smaller energy scales, the eigenvalue distribution approximately assumes the universal semicircle shape, indicating transition to the random-matrix behavior, and in particular that matrix elements become uncorrelated.

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