Fig. 2: The polarization analysis for quantum entangled photons from a van der Waals insulator.

a Illustration of crystal structure of r-BN. H is along the zigzag direction and V is along armchair direction of the crystal. b Coincidence count rate as a function of polarization of pump field in co-polarization configuration, where co-polarization denotes that the polarizations of both collection arms are set to parallel to the pump field. c Coincidence count rate as a function of polarization of pump field in cross-polarization configuration, where cross-polarization denotes that the polarization of one collection arm is set parallel and the other arm perpendicular to the pump field. d–f Coincidence count rate as a function of polarization of the pump field, with the angles of both analyzers fixed at \({0}^{\circ }\), 1\({0}^{\circ }\), \({60}^{\circ }\) relative to the armchair direction. Star symbols represent experimental results, and solid lines indicate the fitted curves.