Advancing our understanding of non-equilibrium phenomena in quantum many-body systems remains one of the greatest challenges in physics. Here we report on the experimental observation of a paradigmatic many-body problem, namely the non-equilibrium dynamics of a quantum impurity immersed in a bosonic environment^1,2. We use an interferometric technique to prepare coherent superposition states of atoms in a Bose–Einstein condensate with a small impurity-state component, and monitor the evolution of such quantum superpositions into polaronic quasiparticles. These results offer a systematic picture of polaron formation^3,4,5,6,7 from weak to strong impurity interactions. They reveal three distinct regimes of evolution with dynamical transitions that provide a link between few-body processes and many-body dynamics. Our measurements reveal universal dynamical behaviour in interacting many-body systems and demonstrate new pathways to study non-equilibrium quantum phenomena.

促进我们对量子多体系统中非平衡现象的理解仍然是物理学中最大的挑战之一。^{在这里，我们报告了一个典型的多体问题的实验观察，即浸入玻色子环境1,2}的量子杂质的非平衡动力学。我们使用干涉技术来制备具有少量杂质态成分的玻色-爱因斯坦凝聚物中原子的相干叠加态，并监测这种量子叠加态向极化子准粒子的演变。这些结果提供了极化子形成的系统图像^3,4,5,6,7从弱到强的杂质相互作用。他们揭示了三种不同的进化机制，它们提供了少体过程和多体动力学之间的联系。我们的测量揭示了相互作用的多体系统中的普遍动力学行为，并展示了研究非平衡量子现象的新途径。