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arXiv 2108.02205cond-mat.stat-mechcond-mat.str-elquant-ph
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动力学约束下的次扩散与多体量子混沌

Subdiffusion and many-body quantum chaos with kinetic constraints

Hansveer Singh, Brayden Ware, Romain Vasseur, Aaron J. Friedman

摘要:

我们研究了具有守恒电荷和动力学约束的多体量子系统的光谱和输运性质。使用随机酉电路,我们计算整体平均的频谱形状因子和线性响应关联函数,并发现它们的特征时间尺度给出了一个有效的哈密顿$-$或等效的,一个转移矩阵描述一个经典的马尔可夫过程的逆间隙。我们的方法使我们能够直接连接的无干扰的时间,$t_{\text{Th}}$,由光谱形状因子,传输特性和线性响应放大器。使用张量网络方法,我们确定的动力学指数,$z$,一些约束,保守的模型。我们发现普遍性类扩散,subdiffusive,quasilocalized,和本地化的动态,这取决于约束的严重程度。特别地,我们证明了具有“Fredkin约束”的量子系统表现出动力学指数为$z \simeq 8/3$的反常输运。

英文摘要:

We investigate the spectral and transport properties of many-body quantum systems with conserved charges and kinetic constraints. Using random unitary circuits, we compute ensemble-averaged spectral form factors and linear-response correlation functions, and find that their characteristic time scales are given by the inverse gap of an effective Hamiltonian$-$or equivalently, a transfer matrix describing a classical Markov process. Our approach allows us to connect directly the Thouless time, $t_{\text{Th}}$, determined by the spectral form factor, to transport properties and linear response correlators. Using tensor network methods, we determine the dynamical exponent, $z$, for a number of constrained, conserving models. We find universality classes with diffusive, subdiffusive, quasilocalized, and localized dynamics, depending on the severity of the constraints. In particular, we show that quantum systems with 'Fredkin constraints' exhibit anomalous transport with dynamical exponent $z \simeq 8/3$.

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