Data and code associated with the paper 'How to use the dispersion in the χ(3) tensor for broadband generation of polarization-entangled photons'

Data and code associated with the following paper V. Vento, et al., Phys. Rev. Res. (2025) A thorough explanation of the experiment performed is available there. The name of each sub-folder and file in S-AS_chi3_code.zip indicates the corresponding figure number ("FIG #") and the type of content ("Data", "Analysis" or "Model").

FIG 1 (a) Sketched amplitude of the two relevant \chi^{(3)} tensor elements in diamond under vertically polarized pump at \omega_p; \Omega_\nu is the Raman-active optical phonon frequency. (c) Stokes spectrum measured by single-photon fiber spectroscopy.

FIG 2 (a) Theoretical amplitude and phase of \chi^{(3)}{VVVV} (solid blue) and \chi^{(3)}{HVVH} (solid red). The Raman and the electronic contributions to the latter are shown as dashed and dotted gray lines, respectively. At the frequencies where \chi^{(3)}{VVVV} and \chi^{(3)}{HVVH} have the same amplitude (black circles), the maximally entangled states \ket{\Psi_\pm} are generated. (b) Frequency-resolved anti-Stokes--Stokes coincidences measured after selecting V (black squares) or H (black circles) polarization in the two detection paths. The data are acquired in 1 hour. The solid blue curve is a polynomial fit that reflects the setup polarization response function since no resonances are expected in this configuration. The solid red curve represents the fit function A\log(I_H(\omega)\ast G(\omega))+b multiplied by the setup response, where the free parameters \Delta = 130.59 cm^{-1}, \sigma_G=24.80 cm^{-1}, A=0.82, b=1.51 are extracted by fitting within the gray region. The dashed red line shows the fit function without convolution, corresponding to the red line in panel (a).

FIG 3 (a-b) Symbols represent the measured CHSH parameters S^{\Psi+}(\omega) (a) and S^{\Psi-}(\omega) (b) extracted from a set of 16 coincidence measurements of 1 hour each. The error bars are calculated by propagating the standard deviation of the coincidence counts in the region [630, 890] cm^{-1}. The shaded domain is delimited by the upper classical bound of 2 and the upper quantum bound of 2\sqrt{2}. The dotted black vertical line indicates the Raman resonance, solid lines are theoretical curves; dashed blue lines are computed without the Raman contribution. In (b) the dashed black curve is computed without accounting for the setup response.

FIG 4 Bell test for different pump polarizations. Shaded gray circles represent the measured CHSH parameter S^{\Psi+}(\omega) for linear pump polarization at \phi = \frac{\pi}{4}. The gray line is the corresponding theoretical curve. The black line represents the theoretical S^{\Psi+}(\omega) for linear pump polarization at \phi=0 (vertical) as in Fig.3(b). The red line represents the theoretical CHSH parameter S^{\Phi-}(\omega) for circular pump polarization, i.e. \phi=\frac{\pi}{4} and \xi=\frac{\pi}{2}. The dotted black vertical line indicates the Raman resonance. The blue region spans between the classical upper bound of 2 and the quantum up