Neyenhuis Brian, Zhang Jiehang, Hess Paul W, Smith Jacob, Lee Aaron C, Richerme Phil, Gong Zhe-Xuan, Gorshkov Alexey V, Monroe Christopher
Joint Quantum Institute and Joint Center for Quantum Information and Computer Science, University of Maryland Department of Physics and National Institute of Standards and Technology, College Park, MD 20742, USA.
Department of Physics, Indiana University, Bloomington, IN 47405, USA.
Sci Adv. 2017 Aug 25;3(8):e1700672. doi: 10.1126/sciadv.1700672. eCollection 2017 Aug.
Although statistical mechanics describes thermal equilibrium states, these states may or may not emerge dynamically for a subsystem of an isolated quantum many-body system. For instance, quantum systems that are near-integrable usually fail to thermalize in an experimentally realistic time scale, and instead relax to quasi-stationary prethermal states that can be described by statistical mechanics, when approximately conserved quantities are included in a generalized Gibbs ensemble (GGE). We experimentally study the relaxation dynamics of a chain of up to 22 spins evolving under a long-range transverse-field Ising Hamiltonian following a sudden quench. For sufficiently long-range interactions, the system relaxes to a new type of prethermal state that retains a strong memory of the initial conditions. However, the prethermal state in this case cannot be described by a standard GGE; it rather arises from an emergent double-well potential felt by the spin excitations. This result shows that prethermalization occurs in a broader context than previously thought, and reveals new challenges for a generic understanding of the thermalization of quantum systems, particularly in the presence of long-range interactions.
尽管统计力学描述了热平衡态，但对于一个孤立量子多体系统的子系统而言，这些状态可能会也可能不会动态出现。例如，接近可积的量子系统通常无法在实验现实的时间尺度内热化，相反，当在广义吉布斯系综（GGE）中纳入近似守恒量时，它们会弛豫到可以用统计力学描述的准静态预热态。我们通过实验研究了在长程横向场伊辛哈密顿量作用下，经过突然淬火后演化的多达22个自旋的链的弛豫动力学。对于足够长程的相互作用，系统弛豫到一种新型的预热态，该状态保留了对初始条件的强烈记忆。然而，这种情况下的预热态不能用标准的GGE来描述；它而是由自旋激发感受到的一种涌现的双阱势产生的。这一结果表明，预热化发生的背景比之前认为的更广泛，并揭示了对量子系统热化进行一般理解所面临的新挑战，特别是在存在长程相互作用的情况下。
