In an ultracold cloud, potassium atoms behave like waves that can add up and amplify each other — much like sound waves in a musical instrument create a loud chord. Physicists have learned to control this process by tuning the strength of atomic interactions with a magnetic field.

It turns out that wave amplification becomes especially strong when the atomic cloud sits at the boundary between two states: a regular gas and a tiny liquid droplet. It's like paints mixing most vividly just before they are fully blended.

This effect could be useful for creating more precise quantum sensors and for entangled pairs of atoms needed in quantum computers.