标题： LGI在耗散量子气体中的量子-经典过渡行为的观测 显示英文标题

标题： Observation of quantum-classical transition behavior of LGI in a dissipative quantum gas

摘要： 勒格特-卡格不等式（LGI）是研究宏观系统中区分量子和经典性质的强大工具。 将LGI应用于具有耗散的非厄米系统提供了一个迷人的机会，因为竞争机制可能会增强或减弱LGI的违反。 一方面，耗散引起的非线性相互作用比厄米系统中的LGI违反更强；另一方面，耗散导致退相干，这可能会减弱LGI的违反。 在本文中，我们研究了一个具有耗散的超冷费米气体的非厄米系统。 我们的实验表明，随着耗散的增加，第三阶LGI参数$K_3$的上限最初上升，在奇异点（EP）达到最大值，其中$K_3 = C_{21} + C_{32} - C_{31}$包含三个两时间关联函数。 超过某个耗散阈值后，LGI的违反减弱，接近经典极限，表明发生了量子到经典过渡（QCT）。 此外，我们观察到LGI的违反随演化时间的增加而减少，加强了时间域中的QCT。 这项研究为利用LGI探索多体开放量子系统中的QCT提供了关键的一步。 显示英文摘要

摘要： The Leggett-Garg inequality (LGI) is a powerful tool for distinguishing between quantum and classical properties in studies of macroscopic systems. Applying the LGI to non-Hermitian systems with dissipation presents a fascinating opportunity, as competing mechanisms can either strengthen or weaken LGI violations. On one hand, dissipation-induced nonlinear interactions amplify LGI violations compared to Hermitian systems; on the other hand, dissipation leads to decoherence, which could weaken the LGI violation. In this paper, we investigate a non-Hermitian system of ultracold Fermi gas with dissipation. Our experiments reveal that as dissipation increases, the upper bound of the third-order LGI parameter $K_3$ initially rises, reaching its maximum at the exceptional point (EP), where $K_3 = C_{21} + C_{32} - C_{31}$, encompassing three two-time correlation functions. Beyond a certain dissipation threshold, the LGI violation weakens, approaching the classical limit, indicating a quantum-to-classical transition (QCT). Furthermore, we observe that the LGI violation decreases with increasing evolution time, reinforcing the QCT in the time domain. This study provides a crucial stepping stone for using the LGI to explore the QCT in many-body open quantum systems.