Physicists at the Institute of Photonic Sciences in Barcelona, Spain have made the most accurate quantum measurement yet, breaking a theoretical limit named for Werner Heisenberg.

They used a beam of photons to measure the small magnetic field produced by a gas made up of a million ultra-cold rubidium atoms.

Normally, the spin of each photon would rotate by a certain amount, due to interactions with the magnetic field of the atoms. A frequency was chosen so that the photons also interacted with each other when they were in the gas, so that the presence of one photon altered the way a second behaved.

These interactions led to a measurement accuracy that grew in proportion to N^-3/2 — greater than Heisenberg’s limit.

The technique, using laser interferometers, could pave the way for more sensitive searches for gravitational waves, which should cause the distance between two objects to change, and the study suggests that the laser interferometers used to look for such changes could be made more precise.