Self-organized criticality is an elegant explanation of how complex structures emerge and persist throughout nature¹, and why such structures often exhibit similar scale-invariant properties^{2,3,4,5,6,7,8,9}. Although self-organized criticality is sometimes captured by simple models that feature a critical point as an attractor for the dynamics^{10,11,12,13,14,15}, the connection to real-world systems is exceptionally hard to test quantitatively^{16,17,18,19,20,21}. Here we observe three key signatures of self-organized criticality in the dynamics of a driven–dissipative gas of ultracold potassium atoms: self-organization to a stationary state that is largely independent of the initial conditions; scale-invariance of the final density characterized by a unique scaling function; and large fluctuations of the number of excited atoms (avalanches) obeying a characteristic power-law distribution. This work establishes a well-controlled platform for investigating self-organization phenomena and non-equilibrium criticality, with experimental access to the underlying microscopic details of the system.

自组织临界是对复杂结构如何在自然界中出现和持续存在的优雅解释¹，以及为什么此类结构经常表现出类似的尺度不变特性^{2、3、4、5、6、7、8、9}。虽然自组织临界有时被简单模型捕获，这些模型将临界点作为动力学的吸引子^{10,11,12,13,14,15}，但与现实世界系统的连接非常难以定量测试^{16,17 ,18,19,20,21}. 在这里，我们观察到超冷钾原子驱动耗散气体动力学中自组织临界的三个关键特征：自组织到很大程度上独立于初始条件的静止状态；最终密度的尺度不变性，以独特的尺度函数为特征；以及服从特征幂律分布的受激原子（雪崩）数量的大幅波动。这项工作建立了一个控制良好的平台，用于研究自组织现象和非平衡临界性，并通过实验访问系统的潜在微观细节。