Meng Xiao

A drop of ink in a glass of water spreads out on its own. But if the ink were made of tiny motors, they wouldn't just spread: they'd crawl, jostle, and cluster into swarms. Such self-propelled particles are called active. You can assemble them into molecules like beads on a bracelet. And here's the surprise: the order of beads on the bracelet changes everything.

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.