Prethermal quasiconserved observables in Floquet quantum systems
Prethermal quasiconserved observables in Floquet quantum systems
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DOI：
10.1103/physrevb.103.054305
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发表时间：
2020-05
影响因子：
3.7
通讯作者：
Chao Yin;Pai Peng;Xiaoyang Huang;C. Ramanathan;P. Cappellaro
中科院分区：
文献类型：
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作者：
Chao Yin;Pai Peng;Xiaoyang Huang;C. Ramanathan;P. Cappellaro
预热化，通过引入新出现的准守恒可观，在指数长时间内保护周期驱动(Floket)多体相方面起着至关重要的作用，而这种准守恒算符的最终命运可以向无限温度发出热化信号。为了阐明多体Floquet系统中预热准守恒的性质，我们系统地分析了可观测量之间的无限温度关联。数值计算表明，自相关的后期行为明确地区分准守恒量和非守恒量，使人们能够挑选出一组线性无关的准守恒量。通过对两个Floquite自旋模型的研究，我们发现了准守恒定律背后的两种不同的机制。首先，我们用数值方法验证了驱动频率较大时的能量准守恒，从而使系统动力学近似地用一个静态的预热哈密顿量来描述。更有趣的是，在中等驱动频率下，如果Floquet驱动包含较大的全局自转，则另一个准服务观测值仍然可以持续存在。我们从理论上说明了如何计算这个守恒量，并给出了数值验证。在系统地确定了所有的准服务可观测项之后，我们终于可以利用从固体核磁共振系统的数值模拟和实验中获得的自关联来研究它们在无限时间极限和热力学极限中的行为。
Prethermalization, by introducing emergent quasiconserved observables, plays a crucial role in protecting periodically driven (Floquet) many-body phases over an exponentially long time, while the ultimate fate of such quasiconserved operators can signal thermalization to infinite temperature. To elucidate the properties of prethermal quasiconservation in many-body Floquet systems, here we systematically analyze infinite-temperature correlations between observables. We numerically show that the late-time behavior of the autocorrelations unambiguously distinguishes quasiconserved observables from nonconserved ones, allowing one to single out a set of linearly independent quasiconserved observables. By investigating two Floquet spin models, we identify two different mechanisms underlying the quasiconservation law. First, we numerically verify energy quasiconservation when the driving frequency is large, so that the system dynamics is approximately described by a static prethermal Hamiltonian. More interestingly, under moderate driving frequency, another quasiconserved observable can still persist if the Floquet driving contains a large global rotation. We show theoretically how to calculate this conserved observable and provide numerical verification. Having systematically identified all quasiconserved observables, we can finally investigate their behavior in the infinite-time limit and thermodynamic limit, using autocorrelations obtained from both numerical simulation and experiments in solid-state nuclear magnetic resonance systems.