论文标题
低维自旋系统中经典和量子密度曲线的时空动力学
Spatiotemporal dynamics of classical and quantum density profiles in low-dimensional spin systems
论文作者
论文摘要
我们提供了量子和经典自旋模型中高温时空相关函数的动力学之间的详细比较。在量子案例中,我们的大规模数字基于量子典型性的概念,该概念利用了这样一个事实,即随机纯量子状态可以忠实地近似整体平均值,从而允许模拟Spin-$ 1/2 $系统,最高$ 40 $ lattice lattice lattice lattice lattice lattice littice。由于希尔伯特(Hilbert)空间的成倍增长,我们发现对于这样的系统大小,即使是单个随机状态也足以产生极低的噪声结果,这对于大多数实际目的而言都是可忽略的。相反,缺少一个经典的典型类似物。特别是,我们证明,为了在经典情况下获得具有相似噪声水平的数据,无论系统大小多大,都需要对经典轨迹进行广泛的平均。着眼于(准)一维自旋链和梯子,我们发现量子和经典动力学之间的一致性非常好。这不仅适用于量子模型和经典模型都是不可集成的情况,而且还适用于量子旋转-1/2 $模型且相应的经典$ S \ to \ infty $模型的情况。我们的分析基于自旋和能量相关函数的时空曲线的比较,在该函数中,该协议不仅在体积中,而且在所得密度分布的尾部中保持。密度曲线的均衡位移反映了新出现的流体动力学的性质,并发现对量子和经典模型表现出相似的缩放比例。
We provide a detailed comparison between the dynamics of high-temperature spatiotemporal correlation functions in quantum and classical spin models. In the quantum case, our large-scale numerics are based on the concept of quantum typicality, which exploits the fact that random pure quantum states can faithfully approximate ensemble averages, allowing the simulation of spin-$1/2$ systems with up to $40$ lattice sites. Due to the exponentially growing Hilbert space, we find that for such system sizes even a single random state is sufficient to yield results with extremely low noise that is negligible for most practical purposes. In contrast, a classical analog of typicality is missing. In particular, we demonstrate that, in order to obtain data with a similar level of noise in the classical case, extensive averaging over classical trajectories is required, no matter how large the system size. Focusing on (quasi-)one-dimensional spin chains and ladders, we find a remarkably good agreement between quantum and classical dynamics. This applies not only to cases where both the quantum and classical model are nonintegrable, but also to cases where the quantum spin-$1/2$ model is integrable and the corresponding classical $s\to\infty$ model is not. Our analysis is based on the comparison of space-time profiles of the spin and energy correlation functions, where the agreement is found to hold not only in the bulk but also in the tails of the resulting density distribution. The mean-squared displacement of the density profiles reflects the nature of emerging hydrodynamics and is found to exhibit similar scaling for quantum and classical models.