Universal Multiport Interferometers for Post‐Selected Multi‐Photon Gates

It is showed how to use universal multiport interferometers' schemes in order to create photonic post-selected Controlled-Z and Controlled–Controlled-Z gates, which are equivalent, modulo single-qubit gates, to Controlled-NOT and Toffoli gates, respectively. The new proposed method is based on the following ingredients: identical single photons, Mach–Zehnder interferometer networks, single-photon detectors and post-selection. In particular, by using dual-rail path encoding together with auxiliary paths and single photons, the success probabilities of such gates is improved. This result further proves the complexity and richness of Reck and Clements schemes beyond the usual notions and practices of Boson Sampling.