arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2002.00411cond-mat.stat-mechcond-mat.str-el
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基于典型性估计的有限尺寸标度

Finite-size scaling of typicality-based estimates

J. Schnack, J. Richter, T. Heitmann, J. Richter, R. Steinigeweg

摘要:

根据典型性的概念,系综平均值可以精确地近似为从高维希尔伯特空间随机抽取的单个纯态的期望值。这种随机向量近似或迹估计器提供了一种强大的方法,例如,热力学量的系统与大希尔伯特空间的大小,这通常不能被视为准确,分析或数值。在这里,我们讨论了有限尺寸标度的准确性,这样的跟踪估计从两个角度。首先,我们研究了随机向量期望值的全概率分布,其次,标准差的全温度依赖性。借助数值例子,我们发现明显的高斯概率分布和预期的标准差随系统大小的减少,至少在某些系统特定的温度以上。低于并且特别是对于小于激励间隙的温度,简单的规则不可用。

英文摘要:

According to the concept of typicality, an ensemble average can be accurately approximated by an expectation value with respect to a single pure state drawn at random from a high-dimensional Hilbert space. This random-vector approximation, or trace estimator, provides a powerful approach to, e.g., thermodynamic quantities for systems with large Hilbert-space sizes, which usually cannot be treated exactly, analytically or numerically. Here, we discuss the finite-size scaling of the accuracy of such trace estimators from two perspectives. First, we study the full probability distribution of random-vector expectation values and, second, the full temperature dependence of the standard deviation. With the help of numerical examples, we find pronounced Gaussian probability distributions and the expected decrease of the standard deviation with system size, at least above certain system-specific temperatures. Below and in particular for temperatures smaller than the excitation gap, simple rules are not available.

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