Fig. 4. Deterministic control of quantum interferences.

(A) Nonclassical interference contrast measured for two photons mapped onto a superposition of two output states with different phase settings (ϕ_H, ϕ_V). The nonclassical contrast is defined as C = (R_δ=0 − R_{δ=0.4 mm})/R_{δ=0.4 mm}, where R_δ is the two-photon coincidence rate of the targeted output state ${\widehat{\mathit{a}}}_{|{\mathit{X}}_2\rangle }^{+}{\widehat{\mathit{a}}}_{|{\mathit{Y}}_3\rangle }^{+}|0\rangle$ at a path length difference of δ. Contrast values are measured with 8 × 8 = 64 phase settings. (B) Contrast values for three phase settings [(α), (ϕ_H = 0, ϕ_V = 0); (β), (ϕ_H = 0, ϕ_V = π/2)_; (γ), (ϕ_H = 0, ϕ_V = π)] as a function of the path length difference between input photons δ. The observed effects are consistent with the initial indistinguishability of the photons evaluated with a HOM experiment (see the Supplementary Materials). Data are acquired for 290 s with a coincidence window of 2.5 ns.