  In the classical Hong-Ou-Mandel (HOM) effect pairs of photons with bosonic
(fermionic) spatial wavefunction coalesce (anti-coalesce) when mixed on a
lossless beamsplitter. Here we report that the presence of dissipation in the
beamsplitter allows the observation of the anti-HOM effect, where bosons
anti-coalesce and fermions show coalescent-like behavior. We provide an
experimental demonstration of the anti-HOM effect for both bosonic and
fermionic two-photon entangled states. Beyond its fundamental significance, the
anti-HOM effect offers applications in quantum information and metrology where
states of entangled photons are dynamically converted.
