Multiport Cyclic Interferometer For Genuine n-photon Indistinguishability Assessment

The generation of quantum states of many indistinguishable photons is a crucial resource for the realization of photonic computer architectures that can enable a quantum speedup and create fault-tolerant multi-party quantum networks. On the experimental side, the measurement of indistinguishability for a multi-photon state is a challenging task. In the case of a two-photon state, the photon indistinguishability is fully assessed by the visibility of the interference fringe of the Hong-Ou-Mandel (HOM) interference experiment on a balanced beam splitter. However, pairwise HOM experiments are unable to completely determine the multi-photon indistinguishability when more than two photons are involved [1-2].