Enhanced quantum correlations from joint pump and photon pair scattering

Scattering of non-classical light is enabling new ways to study and control photon transport. However, advances in this field often rely on simplifying assumptions regarding the quantum light’s generation and its source. In this work, we relax some of these assumptions and probe the behavior of entangled photon pairs passing through a disordered layer after being generated by a randomly scattered pump via spontaneous parametric down-conversion. We experimentally demonstrate that when the photon pairs are generated immediately after the pump is scattered, they retain a sharp angular correlation peak even after propagating through a dynamic scattering medium. Beyond this proof-of-principle experiment, we present a comprehensive theoretical and numerical analysis showing that these correlations persist for arbitrary separations between the pair-generation region and the entrance to the disordered medium, with qualitatively distinct behavior depending on whether scattering occurs before or after pair generation. In particular, we analyze how the width and strength of the angular correlations depend on the distance between the generation region and the disordered layer. When the pairs are generated after the pump is scattered, the correlation width increases with distance, while the correlation strength remains approximately constant. In contrast, when the pairs are generated first and subsequently scattered, the correlation width initially broadens and then narrows, accompanied by a modification in correlation strength. These findings represent a crucial step toward understanding quantum light generation in complex media and potentially exploiting it for quantum technologies.