We present the experimental observation of self-organised criticality in the dynamics of a driven-dissipative gas of ultracold atoms and a first characterisation of its universal properties.
Self organisation provides an elegant explanation for how complex structures emerge and persist throughout nature and society. Surprisingly often, these self-organised structures are found to exhibit remarkably similar fractal-like or scale-invariant properties. While this is sometimes captured by simple models featuring a critical point as an attractor for the dynamics, the connection to real-world complex systems is exceptionally hard to test quantitatively. We show that the competition between facilitated excitation and population decay gives rise to complex nonlinear dynamics that drives the system to a stationary state that is largely independent of the initial conditions and exhibits scale invariance as well as a strong response to perturbations. This establishes a well-controlled platform for investigating self-organisation phenomena and non-equilibrium universality with unprecedented experimental access to the underlying microscopic details of the system.