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arXiv 2006.07304cond-mat.stat-mechhep-thmath-phmath.MPnlin.CDquant-ph
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扰动对偶酉电路中的关联:有效的路径积分公式

Correlations in Perturbed Dual-Unitary Circuits: Efficient Path-Integral Formula

Pavel Kos, Bruno Bertini, Tomaž Prosen

摘要:

具有明确可达的时空关联函数的相互作用多体系统是极其罕见的,特别是在缺乏可积性的情况下。最近,我们发现了一类显著的这样的系统,并称之为双酉量子线路。这些是砖墙型的局部量子线路,其动力学在时间和空间上都是幺正的。对于这些系统,时空关联函数仅在因果光锥的边缘处是非平凡的,并且可以根据一维传递矩阵来计算。然而,双酉性需要微调,所观察到的动力学特征的普遍性程度仍然不清楚。在这里,我们解决这个问题,通过引入任意扰动的本地门。考虑固定扰动,我们证明了,对于一类特殊的未扰动的基本双酉门的关联函数仍然表示在一维传输矩阵。然而,这些矩阵现在在连接原点到因果光锥内的固定端点的通用路径上收缩。关联函数作为所有这些路径上的总和给出。我们的声明是严格的“稀释限制”,只有一小部分的门是扰动,并在随机纵向场的存在下,但我们提供的理论论据和严格的数值检查支持其有效性,即使在干净的情况下,当所有的门都扰动。作为一个副产品,在随机纵向场的情况下-这原来是等价于某些经典的马尔可夫链-我们发现四种类型的非对偶酉(和不可积)相互作用的多体系统的关联函数正是由路径和公式。

英文摘要:

Interacting many-body systems with explicitly accessible spatio-temporal correlation functions are extremely rare, especially in the absence of integrability. Recently, we identified a remarkable class of such systems and termed them dual-unitary quantum circuits. These are brick-wall type local quantum circuits whose dynamics are unitary in both time and space. For these systems the spatio-temporal correlation functions are non-trivial only at the edge of the causal light cone and can be computed in terms of one-dimensional transfer matrices. Dual-unitarity, however, requires fine-tuning and the degree of generality of the observed dynamical features remained unclear. Here we address this question by introducing arbitrary perturbations of the local gates. Considering fixed perturbations, we prove that for a particular class of unperturbed elementary dual-unitary gates the correlation functions are still expressed in terms of one-dimensional transfer matrices. These matrices, however, are now contracted over generic paths connecting the origin to a fixed endpoint inside the causal light cone. The correlation function is given as a sum over all such paths. Our statement is rigorous in the "dilute limit", where only a small fraction of the gates is perturbed, and in the presence of random longitudinal fields, but we provide theoretical arguments and stringent numerical checks supporting its validity even in the clean case and when all gates are perturbed. As a byproduct, in the case of random longitudinal fields -- which turns out to be equivalent to certain classical Markov chains -- we find four types of non-dual-unitary(and non-integrable) interacting many-body systems where the correlation functions are exactly given by the path-sum formula.

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