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arXiv 2005.13558cond-mat.dis-nn
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本征态在多体局域化跃迁时在所有长度尺度上杂化

Eigenstates hybridize on all length scales at the many-body localization transition

Benjamin Villalonga, Bryan K. Clark

摘要:

在足够大的无序度下,相互作用量子系统可以从遍历相过渡到多体局域相。这两个阶段是从根本上不同的动力学性质,其特点是高度激发本征态的哈密顿量。每一个本征态都可以用系统的运动积分(局部的,在MBL相)上的量子数集来表征。本文研究了无序海森堡模型的本征态随无序度$W$的变化规律。我们专注于两个“碰撞”的本征态杂交的概率作为一个函数的范围$R$,在它们不同,以及它们的杂交强度。我们发现,在MBL阶段,碰撞本征态的概率在$R$范围内强烈杂交$Pr(R)\propto \exp [-R/η]$衰减,长度尺度$η(W) = 1 / (B \log(W / W_c) )$在临界无序强度$W_c$发散。这导致在过渡的范围不变性,这表明在所有范围内形成的共振猫态。这种范围不变性不会存活到遍历阶段,在遍历阶段,杂交在大范围内以指数方式更有可能,这一事实可以用简单的组合论证来理解。事实上,补偿这些组合效应使我们能够定义一个额外的相关长度$ξ$在MBL阶段,这是在良好的协议与以前的作品,并采取了临界值$1 / \log(2)$在过渡,发现在以前的作品不稳定的MBL阶段。最后,我们表明,在MBL相位杂交的深度是由两个能级碰撞的本征态接近的能量。

英文摘要:

An interacting quantum system can transition from an ergodic to a many-body localized (MBL) phase under the presence of sufficiently large disorder. Both phases are radically different in their dynamical properties, which are characterized by highly excited eigenstates of the Hamiltonian. Each eigenstate can be characterized by the set of quantum numbers over the set of (local, in the MBL phase) integrals of motion of the system. In this work we study the evolution of the eigenstates of the disordered Heisenberg model as the disorder strength, $W$, is varied adiabatically. We focus on the probability that two `colliding' eigenstates hybridize as a function of both the range $R$ at which they differ as well as the strength of their hybridization. We find, in the MBL phase, that the probability of a colliding eigenstate hybridizing strongly at range $R$ decays as $Pr(R)\propto \exp [-R/η]$, with a length scale $η(W) = 1 / (B \log(W / W_c) )$ which diverges at the critical disorder strength $W_c$. This leads to range-invariance at the transition, suggesting the formation of resonating cat states at all ranges. This range invariance does not survive to the ergodic phase, where hybridization is exponentially more likely at large range, a fact that can be understood with simple combinatorial arguments. In fact, compensating for these combinatorial effects allows us to define an additional correlation length $ξ$ in the MBL phase which is in excellent agreement with previous works and which takes the critical value $1 / \log(2)$ at the transition, found in previous works to destabilize the MBL phase. Finally, we show that deep in the MBL phase hybridization is dominated by two-level collisions of eigenstates close in energy.

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