Fig. 4: Testing multiphoton interference.

Benefits of multiphoton interference using the probe \(\left|3,2\right\rangle\). a Two sets of rates [blue: (5, 0, 3, 2), orange: (3, 2, 3, 2)] measured when the photons are injected inside the interferometer at the same time (data: circles, theory: bold lines) or at different times (data: crosses, theory: dashed line). In the latter case, the photons are well modelled by classical distinguishable particles. Error bars are one standard deviation assuming Poissonian counting statistics. b \({\tilde{{\mathcal{F}}}}_{3,2}(\phi )\) shows a significant improvement in sensitivity in the former case (bold line) compared to the latter case (dashed line), demonstrating that multiphoton interference improved the sensitivity of our probe. Red shaded regions shows 1σ confidence intervals obtained by fitting 50 simulated data sets that are calculated with a Monte Carlo method.