  The experimental characterization of multi-photon quantum interference
effects in optical networks is essential in many applications of photonic
quantum technologies, which include quantum computing and quantum communication
as two prominent examples. However, such characterization often requires
technologies which are beyond our current experimental capabilities, and
today's methods suffer from errors due to the use of imperfect sources and
photodetectors. In this paper, we introduce a simple experimental technique to
characterise multi-photon quantum interference by means of practical laser
sources and threshold single-photon detectors. Our technique is based on
well-known methods in quantum cryptography which use decoy settings to tightly
estimate the statistics provided by perfect devices. As an illustration of its
practicality, we use this technique to obtain a tight estimation of both the
generalized Hong-Ou-Mandel dip in a beamsplitter with six input photons, as
well as the three-photon coincidence probability at the output of a tritter.
