物理学院学术报告（第34期）

报告题目：Computational complexity in quantum chaos and phase transitions

报告专家：周一稼 研究员 上海期智研究院

报告时间：2025年06月25日（周三） 10：00

报告地点：理六栋302      邀请人：李畅

报告摘要：

    Quantum chaos in open systems has attracted considerable attention due to its fundamental ties to statistical physics and practical relevance in quantum platforms such as cold atoms, trapped ions, and superconducting circuits. While signatures of chaos—including level statistics, entanglement entropy, and order parameters—have been extensively characterized in closed systems, their generalization to open quantum systems remains challenging. Here, we investigate the Krylov complexity, an emerging tool for diagnosing quantum chaos, in quantum models that can be realized in Rydberg atom arrays and superconducting circuits. With the example of non-Hermitian spin chains, we reveal two key transitions as disorder strength increases: (1) a chaotic-to-non-chaotic phase transition marked by suppressed growth of Krylov complexity and quantified via reciprocity breaking in Krylov space, and (2) a transition driven by Krylov localization in the weak-disorder regime, indicative of weak ergodicity breaking. These findings align closely with conventional signatures like complex level spacing statistics and entanglement entropy, thereby establishing Krylov complexity as a versatile framework for probing non-Hermitian quantum phase transitions and nonequilibrium dynamics.

专家简介：

    Dr Yijia Zhou earned his Bachelor of Science degree from Fudan University in 2016 and a PhD of physics from University of Nottingham in 2021. Then, he joined the Graduate School of China Academy of Engineering Physics as a postdoc from 2021 to 2023. Currently, Dr Zhou is a postdoc researcher in Shanghai Qi Zhi Institute. Dr Zhou’s research interests span quantum optics, many-body physics and quantum machine learning, with a focus on exploring these topics through the experimental platforms of Rydberg atoms and cavity QED.