Quantum phase transitions, transitions between many-body ground states, are of extensive interest in research ranging from condensed-matter physics to cosmology^1,2,3,4. Key features of the phase transitions include a stage with rapidly growing new order, called inflation in cosmology⁵, followed by the formation of topological defects^6,7,8. How inflation is initiated and evolves into topological defects remains a hot topic of debate. Ultracold atomic gas offers a pristine and tunable platform to investigate quantum critical dynamics^{9,10,11,12,13,14,15,16,17,18,19,20,21}. We report the observation of coherent inflationary dynamics across a quantum critical point in driven Bose–Einstein condensates. The inflation manifests in the exponential growth of density waves and populations in well-resolved momentum states. After the inflation stage, extended coherent dynamics is evident in both real and momentum space. We present an intuitive description of the quantum critical dynamics in our system and demonstrate the essential role of phase fluctuations in the formation of topological defects.

从凝聚态物理到宇宙学^1,2,3,4，量子相变是多体基态之间的转换，在研究中引起了广泛的兴趣。相变的关键特征包括一个快速增长的新秩序的阶段，被称为宇宙学^5中的通货膨胀，其次是拓扑缺陷^6,7,8的形成。通胀如何引发并演变成拓扑缺陷仍然是争论的热点。超冷原子气体提供了一个原始且可调谐的平台来研究量子临界动力学^{9,10,11,12,13,14,15,16,17,18,19,20,21}。我们报告了在驱动的玻色-爱因斯坦凝聚物中一个量子临界点上的相干膨胀动力学的观察结果。通货膨胀表现为密度波和处于良好解析的动量状态的人口的指数增长。在通货膨胀阶段之后，在真实空间和动量空间中，明显的扩展了相干动力学。我们对系统中的量子临界动力学进行了直观的描述，并证明了相位波动在拓扑缺陷形成中的重要作用。