Figure 2

Schematic of the experiment.

The input photon pairs are from a spontaneous parametric down-conversion (SPDC) source and biphotons which implement our dual Fock states, |ψ〉_in = |33〉, are guided to the interferometer with single-mode polarization maintaining optic fibres. These photon states are incident on a polarizing beam splitter and undergo a phase shift between left- and right-circular polarization modes due to the ϕ half-wave plate. The final beam splitter recombines the two circularly-polarized interferometric modes and the output states are measured in the photon number basis by single-photon counting module (SPCM) arrays.