▲ 作者:Daniel Adler, David Wei, Melissa Will, Kritsana Srakaew, Suchita Agrawal, Pascal Weckesser, et al.
▲ 链接:
https://www.nature.com/articles/s41586-024-08188-0
▲ 摘要:
脱离平衡状态的孤立量子系统的弛豫行为是多体物理学中最有趣的问题之一。非平衡态的量子系统通常通过扰乱局部信息和建立纠缠熵而弛豫到热平衡态。然而,哈密顿量中的动力学约束可能导致这一基本范式的崩溃。因为基础希尔伯特空间分裂成动态解耦的子扇区,其中热化被强烈抑制。
研究组通过实验观测了二维倾斜玻色-哈伯德模型中的希尔伯特空间碎片。利用量子气体显微镜,他们设计了各种各样的初始状态,并发现了希尔伯特空间碎片的丰富表现形式,包括体态、界面和缺陷,即二维、一维和零维物体。具体而言,具有相同粒子数和能量的均匀初始态在弛豫动力学上有显著差异。
在整体、非热化的棋盘式状态上插入受控缺陷,研究组观察到高度各向异性的亚维动力学,这是其分形性质的直接标志。局域态和热化态之间的界面依次表现出依据其取向的动力学。该研究结果标志着超越一维的希尔伯特空间碎片的观测,以及伴随的分形直接观察,为深入研究约束系统中的微观输运现象奠定了基础。
▲ Abstract:
The relaxation behaviour of isolated quantum systems taken out of equilibrium is among the most intriguing questions in many-body physics. Quantum systems out of equilibrium typically relax to thermal equilibrium states by scrambling local information and building up entanglement entropy. However, kinetic constraints in the Hamiltonian can lead to a breakdown of this fundamental paradigm owing to a fragmentation of the underlying Hilbert space into dynamically decoupled subsectors in which thermalization can be strongly suppressed. Here we experimentally observe Hilbert space fragmentation in a two-dimensional tilted Bose–Hubbard model. Using quantum gas microscopy, we engineer a wide variety of initial states and find a rich set of manifestations of Hilbert space fragmentation involving bulk states, interfaces and defects, that is, two-, one- and zero-dimensional objects. Specifically, uniform initial states with equal particle number and energy differ strikingly in their relaxation dynamics. Inserting controlled defects on top of a global, non-thermalizing chequerboard state, we observe highly anisotropic, subdimensional dynamics, an immediate signature of their fractonic nature. An interface between localized and thermalizing states in turn shows dynamics depending on its orientation. Our results mark the observation of Hilbert space fragmentation beyond one dimension, as well as the concomitant direct observation of fractons, and pave the way for in-depth studies of microscopic transport phenomena in constrained systems.