Figure 4: Three-photon interference.

(a) The experimentally recorded three-photon interference visibilities (red circles) are compared against the predicted quantum (clear boxes) and classical (blue triangles) results as in Fig. 3. The errors shown on the simulated quantum and classical visibilities were calculated by Monte–Carlo simulation (see Supplementary Methods); errors on the classical visibilities are smaller than the marker size because of the decrease in sensitivity of classical interference to the measured circuit parameters. (b,c) The residuals between the measurements and the calculated classical and quantum visibilities. (d,e) Example four-fold coincidence counts of output channels cdf and bdg when the input photon in mode d is temporally delayed. The shaded area shows the uncertainty in the determined visibility.