Hearing a whisper in a noisy café: that's the same challenge faced by devices that pick up radio waves: the weak signal gets lost in the noise. Scientists from Warsaw used quantum information to let the atoms sort out the mess themselves. They cooled a cloud of rubidium with lasers and turned it into Rydberg atoms (named after Johannes Rydberg)—giants where an electron orbits far from the nucleus. If the nucleus were a pea, the electron would be whizzing around a hundred meters away.

When two such atoms of different kinds get close, they disturb each other so much that both go quiet: this is quantum decoherence. A laser created a superposition (a mix of states), and microwaves gently nudged it. When two signals appeared, the atoms canceled them out through each other, and only single signals reached the detector, as if all the loudmouths had been kicked out of the café.

Paradoxically, the detector only picked up 2% of the light, yet the accuracy of microwave measurement tripled. The idea was predicted by Erwin Schrödinger and John von Neumann, and now confirmed without quantum computers. Such sensors will improve spectroscopy and communications, and the method is like a bouncer: a soft whisper becomes audible only once the loudmouths have left.