Higher-order topological insulators are a novel topological phase beyond the framework of conventional bulk–boundary correspondence^1,2. In these peculiar systems, the topologically non-trivial boundary modes are characterized by a co-dimension of at least two^3,4. Despite several promising preliminary considerations regarding the impact of nonlinearity in such systems^5,6, the flourishing field of experimental higher-order topological insulator research has thus far been confined to the linear evolution of topological states. As such, the observation of the interplay between nonlinearity and the dynamics of higher-order topological phases in conservative systems remains elusive. Here we experimentally demonstrate nonlinear higher-order topological corner states. Our photonic platform enables us to observe nonlinear topological corner states as well as the formation of solitons in such topological structures. Our work paves the way towards the exploration of topological properties of matter in the nonlinear regime, and may herald a new class of compact devices that harnesses the intriguing features of topology in an on-demand fashion.

高阶拓扑绝缘体是一种新的拓扑相，超出了传统体边界对应^1,2的框架。在这些特殊系统中，拓扑非平凡边界模式的特征在于至少两个^3,4的共同维度。尽管关于非线性在此类系统中的影响有几个有希望的初步考虑^5,6，迄今为止，实验性高阶拓扑绝缘体研究的蓬勃发展领域仅限于拓扑状态的线性演化。因此，在保守系统中观察非线性与高阶拓扑相动力学之间的相互作用仍然难以捉摸。在这里，我们通过实验证明了非线性高阶拓扑角状态。我们的光子平台使我们能够观察非线性拓扑角状态以及在这种拓扑结构中形成孤子。我们的工作为探索非线性状态下物质的拓扑特性铺平了道路，并可能预示着一种新的紧凑型设备，它以按需方式利用拓扑的有趣特征。