We directly observe far-field correlations of x-ray photon pairs generated by spontaneous parametric down-conversion (SPDC). Using an energy-resolved, two-dimensional photon counting detector we record the full ring-shaped emission of both photons across a broad bandwidth and extract pair correlations directly from raw events without imposing angular constraints. The ring radii scale with photon energy, in quantitative agreement with transverse phase matching, providing a stringent momentum-space validation of x-ray SPDC. These observations open a route to leveraging quantum correlations in x-ray imaging and metrology, including correlation-enhanced magnification and reduced blurring.
@article{arxiv.2603.16235,
title = {Two-Dimensional Far-Field Correlations of X-ray Photon Pairs},
author = {E. Strizhevsky and Y. Klein and R. Hartmann and S. Francoual and T. Schulli and T. Zhou and A. Sharma and U. Pietsch and L. Strüder D. Altamura and C. Giannini and M. Shokr and S. Shwartz},
journal= {arXiv preprint arXiv:2603.16235},
year = {2026}
}