A cloud of atoms cooled to near absolute zero suddenly starts behaving like a brain. One excited atom triggers a chain reaction — neighbors light up in turn, and an avalanche of activity sweeps through the gas. Physicists call this Rydberg facilitation: atoms are easier to excite when an excited one is nearby. The process is strikingly similar to how neurons exchange electrical signals across synapses.

In the experiment, two phases were clearly separated. The absorbing phase, where avalanches quickly die out. The active phase, where excitation sustains itself. At the boundary between them, the system enters a critical state — the same kind suspected in the working brain. Here, avalanche sizes follow a power law: many small ones, few large ones. And their shapes become universal. The authors confirmed these signatures of criticality for the first time in a controlled physical model.

To keep the system from dying out, the researchers added a controlled pump — a kind of metabolic resource that replenishes lost atoms. This allowed them to hold the gas in a nonequilibrium steady state, like a living organism that constantly expends and restores energy. In the active phase, stochastic oscillations emerged with rare but giant bursts, so-called "dragon avalanches." This regime resembles rhythmic activity of neural networks that accompanies information processing.

The work turns ultracold Rydberg gas into a powerful simulator for neuroscience. Here, one can tune parameters that are nearly elusive in living cells and test theories about how collective behavior of neurons gives rise to complex brain functions.