Witnessing Genuine Multiphoton Indistinguishability published in Physical Review Letters!

Bosonic interference is a fundamental physical phenomenon, and it is believed to lie at the heart of quantum computational advantage. It is thus necessary to develop practical tools to witness its presence, both for a reliable assessment of a quantum source and for fundamental investigations. Here we describe how linear interferometers can be used to unambiguously witness genuine n-boson indistinguishability. The amount of violation of the proposed witnesses bounds the degree of multiboson indistinguishability, for which we also provide a novel intuitive model using set theory. We experimentally implement this test to bound the degree of three-photon indistinguishability in states we prepare using parametric down-conversion. Our approach results in a convenient tool for practical photonic applications, and may inspire further fundamental advances based on the operational framework we adopt.

J. Brod, E. F. Galvao, N. Viggianiello, F. Flamini, N. Spagnolo, F. Sciarrino, Witnessing Genuine Multiphoton Indistinguishability, Phys. Rev. Lett. 122, 063602 (2019).