Polarization state tomography of Stokes-anti-Stokes photon pairs from degenerate four-wave mixing in diamond

Degenerate four-wave mixing in diamond generates a quantum state ρSaS composed of Stokes (S) and anti-Stokes (aS) time-correlated photon pairs (SaS). Here, polarization state tomography of ρSaS is performed in four pertinent scattering configurations: Raman shift in resonance and out of resonance with the phonon energy, and incident light polarized in the direction parallel to or π/4 rotated from a diamond crystallographic axis. We reconstruct the density matrix, calculate concurrence and purity for the four configurations, and directly measure and analyze the diagonal terms of ρSaS in different bases. We establish ρSaS as an entangled linear combination of electronic four-wave mixing and SaS Raman process, mixed with uncorrelated S and aS photons, with the weight constants depending on the scattering conditions, which can be engineered for future applications. © 2024 American Physical Society.