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arXiv 2407.13293hep-thcond-mat.str-elquant-ph
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双标度SYK模型中费米子链的Krylov复杂度与功率谱视角

Krylov complexity of fermion chain in double-scaled SYK and power spectrum perspective

Takanori Anegawa, Ryota Watanabe

AI总结:

本研究通过两点函数计算双标度SYK模型中费米子链的Krylov复杂度,确认低温下指数增长及有界能谱下的初始行为,并用玩具功率谱揭示Lanczos系数的初始线性增长。

摘要:

我们研究了有限温度下双标度SYK(DSSYK)模型中由多个马约拉纳费米子构成的费米子链算符的Krylov复杂度。利用Krylov复杂度可由两点函数计算的事实,我们在两点函数变得简单的极限下进行分析,并将结果与其他先前研究的结果进行比较。我们确认了在极低温度区间内Krylov复杂度的指数增长。一般而言,在任何具有有界能谱的系统中,Krylov复杂度在极晚时刻至多线性增长。因此,我们必须关注初始增长以观察系统或算符行为的差异。由于DSSYK模型正是这样的有界系统,其混沌性质可预期表现为Krylov复杂度的初始指数增长。特别地,Krylov复杂度初始指数增长终止的时间与自由度数目无关。基于上述,我们使用玩具功率谱系统地、具体地研究Lanczos系数和Krylov复杂度,并加深对这些初始行为的理解。特别地,我们确认功率谱的整体类sech行为展示了Lanczos系数的初始线性增长,即使能谱是有界的。

英文摘要:

We investigate Krylov complexity of the fermion chain operator which consists of multiple Majorana fermions in the double-scaled SYK (DSSYK) model with finite temperature. Using the fact that Krylov complexity is computable from two-point functions, the analysis is performed in the limit where the two-point function becomes simple and we compare the results with those of other previous studies. We confirm the exponential growth of Krylov complexity in the very low temperature regime. In general, Krylov complexity grows at most linearly at very late times in any system with a bounded energy spectrum. Therefore, we have to focus on the initial growth to see differences in the behaviors of systems or operators. Since the DSSYK model is such a bounded system, its chaotic nature can be expected to appear as the initial exponential growth of the Krylov complexity. In particular, the time at which the initial exponential growth of Krylov complexity terminates is independent of the number of degrees of freedom. Based on the above, we systematically and specifically study the Lanczos coefficients and Krylov complexity using a toy power spectrum and deepen our understanding of those initial behaviors. In particular, we confirm that the overall sech-like behavior of the power spectrum shows the initial linear growth of the Lanczos coefficient, even when the energy spectrum is bounded.

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