Gaussian models provide an excellent effective description of many quantum many-body systems ranging from condensed-matter systems^1,2 all the way to neutron stars³. Gaussian states are common at equilibrium when the interactions are weak. Recently it was proposed that they can also emerge dynamically from a non-Gaussian initial state evolving under non-interacting dynamics^{4,5,6,7,8,9,10,11}. Here we present the experimental observation of such a dynamical emergence of Gaussian correlations in a quantum many-body system. This non-equilibrium evolution is triggered by abruptly switching off the effective interaction between the observed collective degrees of freedom, while leaving the interactions between the microscopic constituents unchanged. Starting from highly non-Gaussian correlations, consistent with the sine–Gordon model¹², we observe a Gaussian state emerging over time as revealed by the decay of the fourth- and sixth-order connected correlations in the quantum field. A description of this dynamics requires a novel mechanism for the emergence of Gaussian correlations, which is relevant for a wide class of quantum many-body systems. In our closed system with non-interacting effective degrees of freedom, we do not expect full thermalization^{13,14,15,16,17,18,19}. This memory of the initial state is confirmed by observing recurrences²⁰ of non-Gaussian correlations.

高斯模型对从凝聚态系统^1,2一直到中子星³的许多量子多体系统提供了极好的有效描述。当相互作用较弱时，高斯状态在平衡时很常见。最近有人提出，它们也可以从非相互作用动力学下演化的非高斯初始状态动态出现^{4,5,6,7,8,9,10,11}. 在这里，我们展示了量子多体系统中高斯相关性的这种动态出现的实验观察。这种非平衡演化是由突然关闭观察到的集体自由度之间的有效相互作用触发的，同时保持微观成分之间的相互作用不变。从高度非高斯相关性开始，与正弦-戈登模型一致¹²，我们观察到随着时间的推移出现的高斯状态，正如量子场中四阶和六阶连通相关性的衰减所揭示的那样。对这种动力学的描述需要一种新的机制来出现高斯相关性，这与广泛的量子多体系统相关。在我们具有非相互作用有效自由度的封闭系统中，我们不期望完全热化^{13,14,15,16,17,18,19}。这种初始状态的记忆通过观察非高斯相关性的重复^{20得到证实。}