Zhen Gao

Light can get stuck inside tiny structures, like sound in a perfectly tuned bell: the energy does not escape, even though there are no walls around. Such states are called 'bound states in the continuum'—light is trapped but not confined in a box. Until now, they were produced in ordinary crystals, where left and right directions are indistinguishable.

A drummer beats a rhythm, and the drumhead vibrates in time. If you strike often enough, the vibrations overlap, and a nearly stationary zone, a node, forms at the center. A similar effect occurs with microwaves in a material whose properties change over time. When the changes resonate with the wave, its motion freezes.