Building ultrasensitive sensors for light measurements and spectroscopy starts with tiny chambers where light ricochets like an echo in a canyon. Previously, engineers chased the quality factor — the duration of this echo: the longer it rings, the more noticeable the slightest changes.

But the laws of the quantum world, derived from the uncertainty principle, point to a different path. Precision isn't limited by the echo's duration, but by how sharply the wave's phase shifts: that is, the moment when the crest hits the chamber wall. In other words, we should listen not to the volume, but to the shift in rhythm.

This was confirmed by an experiment with a Michelson interferometer — a device that splits light into two beams traveling at the speed of light, then recombines them. It turned out that the optimal tuning lies where the echo has almost faded, but the phase responds most sharply to changes.