A librarian carefully places a book on the shelf and retrieves it on demand without waking the cat sleeping nearby. The new quantum memory works in much the same way: it catches a particle of light, hides it in the vibration of a tiny bridge, and returns it when needed.

Light in optical fibers carries quantum information, but that information needs to be stored somewhere. Conventional storage devices are either too bulky or cannot release light on command. Here, physicists built a silicon chip with a bridge that vibrates very fast. When a photon enters the chip, it makes the bridge shake, and that vibration stores the information.

To write a photon, the physicists use a weak, long light pulse, and to read it out, a short one. The memory held the photon for 150 nanoseconds and returned it on command. The thermal jitter of the bridge stayed below one quantum, meaning nearly zero. The write efficiency is still low, but that only limits the event rate, not the purity of the quantum state. Such a chip could become a node of a quantum repeater or an interface between single-photon sources and optical fiber.