Mohamed Hatifi

A diamond dust particle made of carbon floats in a vacuum on a laser beam. Inside there is a defect: a nitrogen atom next to a vacancy. Under the influence of light and microwaves, it starts to jitter, rocking the entire particle. This is how a sound laser starts: weak random nudges turn into a powerful steady hum.

An ordinary photometry detector can't tell a left photon from a right one. But let it start moving, and everything changes. Imagine a rower moving between two flutists playing the same note. His ear is perfectly tuned to that note and ignores all others. As he moves, the pitch from the flutist ahead sounds higher, and from the one behind sounds lower.