The cooperative modification of spontaneous radiative decay exemplifies a many-emitter effect in quantum optics. So far, its experimental realizations have relied on interactions mediated by rapidly escaping photons, which do not play an active role in the emitter dynamics. Here we use a platform of ultracold atoms in a one-dimensional optical lattice geometry to explore cooperative non-Markovian dynamics of synthetic quantum emitters that decay by radiating slow atomic matter waves. By preparing and manipulating arrays of emitters hosting weakly and strongly interacting many-body phases of excitations, we demonstrate directional collective emission and study the interplay between retardation and super- and subradiant dynamics. Moreover, we directly observe the spontaneous buildup of coherence among emitters. Our results on collective radiative dynamics establish ultracold matter waves as a versatile tool for studying many-body quantum optics in spatially extended and ordered systems.

自发辐射衰变的协同修改是量子光学中多发射器效应的例证。到目前为止，它的实验实现依赖于由快速逃逸的光子介导的相互作用，这些光子在发射器动力学中没有发挥积极作用。在这里，我们使用一维光晶格几何中的超冷原子平台来探索通过辐射慢原子物质波而衰变的合成量子发射器的协作非马尔可夫动力学。通过准备和操纵承载弱相互作用和强相互作用的多体激发相位的发射器阵列，我们展示了定向集体发射，并研究了延迟与超辐射和亚辐射动力学之间的相互作用。此外，我们直接观察到发射机之间自发的相干性建立。我们在集体辐射动力学方面的结果将超冷物质波确立为研究空间扩展和有序系统中的多体量子光学的通用工具。