  Boson bunching is amongst the most remarkable features of quantum physics. A
celebrated example in optics is the Hong-Ou-Mandel effect, where the bunching
of two photons arises from a destructive quantum interference between the
trajectories where they both either cross a beam splitter or are reflected.
This effect takes its roots in the indistinguishability of identical photons.
Hence, it is generally admitted -- and experimentally verified -- that bunching
vanishes as soon as photons can be distinguished, e.g., when they occupy
distinct time bins or have different polarizations. Here we disproof this
alleged straightforward link between indistinguishability and bunching by
exploiting a recent finding in the theory of matrix permanents. We exhibit a
family of optical circuits where the bunching of photons into two modes can be
significantly boosted by making them partially distinguishable via an
appropriate polarization pattern. This boosting effect is already visible in a
7-photon interferometric process, making the observation of this phenomenon
within reach of current photonic technology. This unexpected behavior questions
our understanding of multiparticle interference in the grey zone between
indistinguishable bosons and classical particles.
