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arXiv 1402.2299cond-mat.str-elcond-mat.quant-gascond-mat.stat-mech
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量子自旋链几何猝灭后的纠缠传播

Entanglement spreading after a geometric quench in quantum spin chains

Vincenzo Alba, Fabian Heidrich-Meisner

摘要:

研究了自旋为1/2的各向异性海森堡(XXZ)链在几何猝灭后的纠缠扩展。这对应于链的几何形状的突然变化,或者用被限制在箱形陷阱中的相互作用费米子的等效语言来说,对应于陷阱大小的突然增加。淬火后的纠缠动力学与磁化波前的弹道传播。在自由费米子点(XX链),冯诺伊曼熵S_A表现出几种有趣的动力学状态。具体而言,在短时间内观察到对数增加,类似于局部猝灭。这是准确地描述了一个分析公式,我们从启发式的论点。在中间时刻,短时间动力学的部分恢复与幂律增长S_A t^α叠加,其中α<1。最后,在很长的时间里,一个稳定的状态发展为恒定的纠缠熵。正如所料,由于该模型是可积的,我们发现,该稳态是非热的,虽然它表现出广泛的纠缠熵。我们还研究了从有限链到无限链(突然膨胀)淬火后的纠缠动力学。虽然在很长一段时间的纠缠消失,我们证明了它的弛豫动力学表现出一些标度特性。最后,我们讨论了XXZ链在无带隙相位下的短时纠缠动力学。描述XX链的时间依赖性的相同公式在整个无间隙阶段仍然有效。

英文摘要:

We investigate the entanglement spreading in the anisotropic spin-1/2 Heisenberg (XXZ) chain after a geometric quench. This corresponds to a sudden change of the geometry of the chain or, in the equivalent language of interacting fermions confined in a box trap, to a sudden increase of the trap size. The entanglement dynamics after the quench is associated with the ballistic propagation of a magnetization wavefront. At the free fermion point (XX chain), the von-Neumann entropy S_A exhibits several intriguing dynamical regimes. Specifically, at short times a logarithmic increase is observed, similar to local quenches. This is accurately described by an analytic formula that we derive from heuristic arguments. At intermediate times partial revivals of the short-time dynamics are superposed with a power-law increase S_A t^α, with α<1. Finally, at very long times a steady state develops with constant entanglement entropy. As expected, since the model is integrable, we find that the steady state is non thermal, although it exhibits extensive entanglement entropy. We also investigate the entanglement dynamics after the quench from a finite to the infinite chain (sudden expansion). While at long times the entanglement vanishes, we demonstrate that its relaxation dynamics exhibits a number of scaling properties. Finally, we discuss the short-time entanglement dynamics in the XXZ chain in the gapless phase. The same formula that describes the time dependence for the XX chain remains valid in the whole gapless phase.

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