Fig. 3: Hong-Ou-Mandel coincidence measurements.

a Normalized coincidence counts \(\left( {{C}_{13} + {C}_{23}} \right)\) between the two output channels of the metasurface for a variation of the initial photon time delay. The high visibility beyond the classical limit of 50% confirms the expected quantum interference effect. The reference is obtained for a standard Hong-Ou-Mandel experiment with a standard beam splitter to characterize the quality of the photon source. b Normalized coincidence counts C₁₂ between detectors D₁ and D₂ for the measurement with the polarization beam splitter in one output channel of the metasurface. The peak in the coincidence counts of the “anti”-HOM measurement confirms that the two photons always take the same output channel