Experimental quantum interference of distinguishable sets of indistinguishable photons

Quantum interference of indistinguishable bosonic particles is indispensable for the description of many quantum optical experiments. As in the famous Hong-Ou-Mandel effect, symmetry of the input state as well as symmetries in the scattering scenario can lead to destructive interference with the suppression of a large number of output events. The rules specifying which input-output combinations interfere totally destructively are summarized in so-called suppression laws. Here, we experimentally investigate the suppression law of the J_x unitary in a femtosecond laser-written waveguide structure with 4 photons emitted from a SPDC source. We show that totally destructive interference does not require mutual indistinguishability between all particles but only between symmetrically paired ones, which is in agreement with recent theoretical predictions. The experimental results are compared to a theoretical model of the experiment, where we consider higher order emission of the source, partial distinguishability, and photon loss.