Metrologia 56, 015016 (2019)

Sources emitting single photons are one of the key elements in emerging quantum optical technologies. During the development phase of devices for, say, radiometry with single photons, a fair comparison between the various stages requires common standards — a necessity that becomes even more important when the device is rolled out for mass production. But so far, there are no universal means to characterize single-photon sources.

Ekaterina Moreva and colleagues from the National Metrology Institutes of Italy, Germany and the UK have now joined forces to develop the first standardized technique to characterize single-photon sources and to provide common uncertainty estimation procedures. Using a Hanbury Brown and Twiss interferometer, the authors measured the coincidence and click probabilities from single photons emitted from a nitrogen–vacancy centre in diamond, allowing them to estimate the second-order correlation function — a parameter commonly used to describe single-photon sources. The independent results agree within uncertainty and mark the first step towards an international measurement standard for single-photon sources.