Quantum fluids of light are an emerging platform for energy-efficient signal processing, ultrasensitive interferometry and quantum simulators at elevated temperatures. Here we demonstrate all-optical control of the topological excitations in a large polariton condensate realizing the bosonic analogue of a long Josephson junction and inducing the nucleation of Josephson vortices. When a phase difference is imposed at the boundaries of the condensate, two extended regions become separated by a sharp phase jump of π radians and a solitonic depletion of the density, forming an insulating barrier with a suppressed order parameter. The superfluid behaviour—characterized by a smooth phase gradient across the system instead of the sharp phase jump—is recovered at higher polariton densities and is mediated by the nucleation of Josephson vortices within the barrier. Our results contribute to the understanding of dissipation and stability of elementary excitations in macroscale quantum systems.

光的量子流体是在高温下进行节能信号处理，超灵敏干涉测量和量子模拟器的新兴平台。在这里，我们展示了在大极化子冷凝物中对拓扑激发的全光控制，实现了长约瑟夫森结的玻色子类似物并诱导了约瑟夫森涡旋的成核作用。当在冷凝物的边界处施加相位差时，两个扩展区域将被π弧度的急剧相跳和密度的孤子损耗所分隔，从而形成具有受抑制的阶数参数的绝缘势垒。超流体行为（通过整个系统中的平滑相梯度而不是尖锐的相跳来表征）在较高的极化子密度下得以恢复，并由势垒内的约瑟夫森涡核形核来介导。我们的结果有助于理解宏观量子系统中基本激发的耗散和稳定性。