Scientists finally detected a quantum effect that blocks atoms from scattering light

When all available quantum states are full, ultracold atom clouds become more transparent

a dense cloud of atoms, illustrated as blue spheres, with light waves bouncing off them

In an ultracold, dense cloud of atoms (blue), a quantum effect dictates whether atoms scatter light (red arrows). If the quantum states are fully occupied, the atoms cannot change quantum states and the light isn’t scattered.

Illustration by Steven Burrows/JILA

A cloud of ultracold atoms is like a motel with a neon “no vacancy” sign.