Daniel Oi, John Jeffers and Václav Potoček have shown how to measure nothing. Specifically, they showed how to find out whether there are any photons in a quantum field without disturbing its coherence in the case the vacuum is not found. This requires that no information is gained about the number of photons in the field, apart from the fact that there is at least one.

 They suggest using a three-level atom controlled by a laser to probe the field stored in a cavity using an adiabatic transition. Moreover, modelling suggests that the process is robust against common sources of imperfection. The results have been selected to be an Editor’s Suggestion in Physical Review Letters Phys. Rev. Lett. 110, 210504 (2013) and are spotlighted in the Synopsis section of Physics