Zhengyang Bai

Ordinary light scatters in all directions, but physicists turned it into something like a conveyor belt — a one-way stream that doesn't turn back. To do this, they sent two counter-propagating beams through a cloud of Rydberg atoms, bloated to the size of a tiny dust speck.

In nature, everything is cyclical: hares multiplied — foxes thrived — hares ran out — foxes died off — and the cycle repeated. This 'predator-prey' model was invented a century ago, and it works everywhere: from chemistry to economics. Physicists have now brought this storyline to the atomic stage.

A forest fire that puts itself out and then relights itself: that is what a quantum limit cycle, discovered in a new theoretical model, looks like. In an open quantum system, where particles constantly exchange energy with their surroundings, periodic oscillations arise not in spite of noise but because of it.