  Multi-photon interference in large multi-port interferometers is key to
linear optical quantum computing and in particular to boson sampling. Silicon
photonics enables complex interferometric circuits with many components in a
small footprint and has the potential to extend these experiments to larger
numbers of interfering modes. However, loss has generally limited the
implementation of multi-photon experiments in this platform. Here, we make use
of high-efficiency grating couplers to combine bright and pure quantum light
sources based on ppKTP waveguides with silicon circuits. We interfere up to 5
photons in up to 15 modes, verifying genuine multi-photon interference by
comparing the results against various models including partial
distinguishability between photons.
