A swing, if pushed in a special pattern, remembers how hard and when it was pushed. A tiny mirror behaves much the same way under the blows of laser pulses. Light pushes the mirror, making it vibrate, and the pattern of these vibrations stores the history of impacts.

By changing the pulse shape, from smooth to sharp, you can control the mirror's transitions between states. It either flows smoothly or jumps abruptly, as if going up steps. At the same time, the past doesn't vanish: the mirror retains a trace of previous pushes — a property called hysteresis.

To gauge how tenaciously the mirror remembers past signals, scientists introduced a simple metric — a geometric form factor that measures how much the memory orders information. The data is read by analyzing the light reflected from the vibrating mirror: spectroscopy and photometry capture the slightest imprints of the past.

The surprising part is that the pulse shape can be tuned so precisely that the mirror jumps between states, skipping intermediate ones, like an elevator with discrete floors. This mechanical vibration-based memory is hundreds of times more durable than electronic memory — thermal noise barely threatens it. Mirrors can easily be integrated into existing optical chips, accelerating the development of reliable quantum communication and computers.