Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck, Austria.
The Rudolf Peierls Centre for Theoretical Physics, Oxford University, Oxford OX1 3NP, United Kingdom.
Phys Rev Lett. 2014 Oct 31;113(18):187203. doi: 10.1103/PhysRevLett.113.187203. Epub 2014 Oct 30.
Signal propagation in the nonequilibrium evolution after quantum quenches has recently attracted much experimental and theoretical interest. A key question arising in this context is what principles, and which of the properties of the quench, determine the characteristic propagation velocity. Here we investigate such issues for a class of quench protocols in one of the central paradigms of interacting many-particle quantum systems, the spin-1/2 Heisenberg XXZ chain. We consider quenches from a variety of initial thermal density matrices to the same final Hamiltonian using matrix product state methods. The spreading velocities are observed to vary substantially with the initial density matrix. However, we achieve a striking data collapse when the spreading velocity is considered to be a function of the excess energy. Using the fact that the XXZ chain is integrable, we present an explanation of the observed velocities in terms of "excitations" in an appropriately defined generalized Gibbs ensemble.
在量子淬火后的非平衡演化中信号的传播最近引起了很多实验和理论上的兴趣。在这种情况下出现的一个关键问题是，淬火的哪些原理和特性决定了特征传播速度。在这里，我们研究了一类在相互作用多粒子量子系统的中心范例之一，即自旋 1/2 Heisenberg XXZ 链中的淬火协议。我们考虑了从各种初始热密度矩阵到相同最终哈密顿量的淬火，使用矩阵乘积态方法。观察到扩展速度随初始密度矩阵而显著变化。然而，当将扩展速度视为过量能量的函数时，我们实现了引人注目的数据崩溃。利用 XXZ 链是可积的事实，我们根据在适当定义的广义吉布斯系综中的“激发”，给出了对观察到的速度的解释。
