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arXiv 2303.02181cond-mat.stat-mechcond-mat.dis-nnhep-th
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离散量子场论中的热化和局域化

Thermalization and localization in a discretized quantum field theory

Spasen Chaykov, Brenden Bowen, Nishant Agarwal

摘要:

定域化标志着量子多体系统在存在足够大的无序时的次区域热化的崩溃。在本文中,我们使用数值方法来研究耦合量子谐振子多体系统的热化和局域化,该系统是通过离散Minkowski时空中的标量量子场论得到的。我们考虑一个高斯初始状态,通过一个全球性的质量淬火,与二次哈密顿量,并解决系统的精确动力学没有和无序在一个和两个空间维度。我们发现,在这两种情况下,有限大小的系统本地化足够大的混乱,这样的纠缠熵的子区域保持其初始面积定律的行为,系统不再开发远程相关。为了进一步探测热化到本地化的过渡,我们定义了一个频率间隙比,测量相邻的间隙在相空间的本征值的哈密顿量,并研究它如何随无序强度和系统的大小。我们发现在两个空间维度的中间无序的混沌政权的签名,并认为这是一个有限尺寸的效果,这样的系统将本地化任意小的障碍在连续的一个和两个空间维度,符合安德森局域化。最后,我们使用的频率间隙比认为,在三个空间维度,另一方面,该系统只会本地化的无序强度在连续的临界值以上,再次符合安德森局域化。

英文摘要:

Localization marks the breakdown of thermalization in subregions of quantum many-body systems in the presence of sufficiently large disorder. In this paper, we use numerical techniques to study thermalization and localization in a many-body system of coupled quantum harmonic oscillators obtained by discretizing a scalar quantum field theory in Minkowski spacetime. We consider a Gaussian initial state, constructed through a global mass quench, with a quadratic Hamiltonian, and solve for the system's exact dynamics without and with disorder in one and two spatial dimensions. We find that finite-size systems localize for sufficiently large disorder in both cases, such that the entanglement entropy of subregions retains its initial area-law behavior, and the system no longer develops long-range correlations. To probe the thermalization-to-localization transition further, we define a frequency gap ratio that measures adjacent gaps in the phase space eigenvalues of the Hamiltonian and study how it varies with disorder strength and system size. We find signatures of a chaotic regime at intermediate disorder in two spatial dimensions and argue that it is a finite-size effect, such that the system would localize for arbitrarily small disorder in the continuum in both one and two spatial dimensions, consistent with Anderson localization. Lastly, we use the frequency gap ratio to argue that in three spatial dimensions, on the other hand, the system would only localize for disorder strengths above a critical value in the continuum, again consistent with Anderson localization.

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