A neat stack of atomic layers lies on a substrate. An invisible beam of terahertz light shines down on it, with a magnetic field applied from the side. After reflection, the beam's polarization rotates slightly.
In a tight row of atoms, spaced closer than the wavelength of light, a remarkable state hides. The excitation is distributed among all particles so that their radiation cancels itself out. This quantum 'silence' is an ideal vault for a photon: it can be stored there hundreds of times longer than usual.