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arXiv 2407.01682quant-phcond-mat.dis-nncond-mat.quant-gas
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用于键无序海森堡自旋模型的簇截断维格纳近似

Cluster truncated Wigner approximation for bond-disordered Heisenberg spin models

Adrian Braemer, Javad Vahedi, Martin Gärttner

AI总结:

本研究针对键无序海森堡自旋链的淬火动力学,提出受SDRG/RSRG启发的聚类策略优化cTWA的聚类选择,还提出离散采样方案替代原高斯近似方案,提升了计算准确性并降低蒙特卡洛散粒噪声。

摘要:

我们对应用于具有幂律相互作用的键无序海森堡自旋链中的淬火动力学的簇截断维格纳近似(cluster Truncated Wigner Approximation, cTWA)开展了全面的数值研究。我们发现,cTWA在很宽的参数范围内都能得到高度准确的结果。不过,其准确性取决于簇的合适选择。通过采用受强无序重整化群(strong disorder renormalisation group, SDRG)/实空间重整化群(real-space renormalization group, RSRG)启发的聚类策略,在强无序区域,仅需两个自旋构成的簇就足以得到基本精确的结果。令人意外的是,即便对于相当弱的无序(例如存在超长程相互作用的情况),这种聚类选择的表现也优于朴素的连续自旋簇选择。此外,我们提出了一种初始维格纳函数的离散采样方案,作为最初引入的基于高斯近似方案的替代方案。该采样方案使cTWA在概念上与单自旋的常规dTWA处于同等地位,并且与高斯方案相比,蒙特卡洛散粒噪声有所降低。

英文摘要:

We present a comprehensive numerical investigation of the cluster Truncated Wigner Approximation (cTWA) applied to quench dynamics in bond-disordered Heisenberg spin chains with power-law interactions. We find that cTWA yields highly accurate results over a wide parameter range. However, its accuracy hinges on a suitable choice of clusters. By using a clustering strategy inspired by the strong disorder renormalisation group (SDRG)/real-space renormalization group (RSRG), clusters of two spins are sufficient to obtain essentially exact results in the regime of strong disorder. Surprisingly, even for rather weak disorder, e.g.\ in the presence of very long-range interactions, this choice of clustering outperforms a naive choice of clusters of consecutive spins. Additionally, we develop a discrete sampling scheme for the initial Wigner function, as an alternative to the originally introduced scheme based on Gaussian approximations. This sampling scheme puts cTWA on the same conceptional footing as regular dTWA for single spins and yields some reduction in the Monte Carlo shot noise compared to the Gaussian scheme.

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