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arXiv 2104.00472cond-mat.stat-mechcond-mat.str-el
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自旋模型中的量子动力学与经典动力学:链、梯子和正方形晶格

Quantum versus Classical Dynamics in Spin Models: Chains, Ladders, and Square Lattices

Dennis Schubert, Jonas Richter, Fengping Jin, Kristel Michielsen, Hans De Raedt, Robin Steinigeweg

摘要:

我们提出了一个全面的比较自旋和能量动力学在量子和经典自旋模型上不同的几何形状,从一维链,准一维梯子,二维正方形晶格。聚焦于形式上无限温度下的动力学,我们特别考虑了局域密度的自相关函数,其中时间演化要么由量子情形下的线性薛定谔方程控制,要么由经典力学情形下的非线性哈密顿运动方程控制。虽然,在充分的一般性,量子和经典动力学之间的定量协议,因此不能预期,我们的大规模的数值结果自旋$1/2$系统高达$N = 36$晶格网站,事实上违背了这一期望。具体来说,我们观察到一个非常好的协议,所有的几何形状,这是最好的不可积量子模型在准一维或二维,但仍然令人满意的情况下,可积链,至少如果输运性质不占主导地位的大量守恒定律。我们的研究结果表明,经典或半经典模拟提供了一个有意义的策略来分析量子多体模型的动力学,即使在自旋量子数$S = 1/2$是小的,远离经典极限$S \to \infty$的情况下。

英文摘要:

We present a comprehensive comparison of spin and energy dynamics in quantum and classical spin models on different geometries, ranging from one-dimensional chains, over quasi-one-dimensional ladders, to two-dimensional square lattices. Focusing on dynamics at formally infinite temperature, we particularly consider the autocorrelation functions of local densities, where the time evolution is governed either by the linear Schrödinger equation in the quantum case, or the nonlinear Hamiltonian equations of motion in the case of classical mechanics. While, in full generality, a quantitative agreement between quantum and classical dynamics can therefore not be expected, our large-scale numerical results for spin-$1/2$ systems with up to $N = 36$ lattice sites in fact defy this expectation. Specifically, we observe a remarkably good agreement for all geometries, which is best for the nonintegrable quantum models in quasi-one or two dimensions, but still satisfactory in the case of integrable chains, at least if transport properties are not dominated by the extensive number of conservation laws. Our findings indicate that classical or semi-classical simulations provide a meaningful strategy to analyze the dynamics of quantum many-body models, even in cases where the spin quantum number $S = 1/2$ is small and far away from the classical limit $S \to \infty$.

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