Steam rising from hot metal is a familiar sight in the kitchen. But if you use rubidium instead of water, that cloud becomes a battery. It doesn't run on chemical reactions but on the quantum coordination of atoms.

In the experiment, a vapor cloud with a trillion rubidium atoms (an alkali metal similar to sodium) was placed in a glass cell. The atoms behaved like a single orchestra: their spins (internal "tops") rotated in sync. This state is quantum coherence — when many particles act as one whole rather than a crowd of individuals. This coordination allowed energy to be stored. The battery's capacity was measured directly — without complex tomography, simply by counting the available energy in different cloud states. It turned out that coherence greatly increases capacity, even if the number of excited atoms doesn't change.

When a magnetic field was added to the system, the atoms' coordination began to break down, as if musicians in an orchestra each started playing on their own. Along with the loss of coherence, capacity also dropped. The scientists traced a clear link: the less order, the less energy can be stored. This relationship is described by entropy — a measure of disorder. Thus, the vapor cloud became a tangible model of quantum thermodynamics, where you can touch the connection between energy and information.

So, hot vapor isn't just heat: it's a potential reservoir of quantum energy. And the more cooperatively atoms work, the more they can store.