article published yes A. Becker author Georgios Koutentakis author d7b23d3a-9e21-11ec-b482-f76739596b95 P. Schmelcher author MiLe department Coherent Optical Metrology Beyond Electric-Dipole-Allowed Transitions project Kapitza-Dirac scattering, the diffraction of matter waves from a standing light field, is widely utilized in ultracold gases, but its behavior in the strongly interacting regime is an open question. Here, we develop a numerically exact two-body description of Kapitza-Dirac scattering for two contact-interacting atoms in a one-dimensional harmonic trap subjected to a pulsed optical lattice, enabling us to obtain the numerically exact dynamics. We map how interaction strength, lattice depth, lattice wave number, and pulse duration reshape the diffraction pattern, leading to an interaction-dependent population redistribution in real and momentum space. By comparing the exact dynamics to an impulsive sudden-approximation description, we delineate the parameter regimes where it remains accurate and those, notably at strong attraction and small lattice wave number, where it fails. Our results provide a controlled few-body benchmark for interacting Kapitza-Dirac scattering and quantitative guidance for Kapitza-Dirac-based probes of ultracold atomic systems. https://research-explorer.ista.ac.at/download/21660/21667/2026_PhysicalReviewResearch_Becker.pdf application/pdfno American Physical Society2026 eng 2643-1564 2512.1526010.1103/rdsn-stlq 8 Becker, A., Koutentakis, G., &#38; Schmelcher, P. (2026). Two-body Kapitza-Dirac scattering of one-dimensional ultracold atoms. <i>Physical Review Research</i>. American Physical Society. <a href="https://doi.org/10.1103/rdsn-stlq">https://doi.org/10.1103/rdsn-stlq</a> A. Becker, G. Koutentakis, P. Schmelcher, Physical Review Research 8 (2026). Becker, A., Georgios Koutentakis, and P. Schmelcher. “Two-Body Kapitza-Dirac Scattering of One-Dimensional Ultracold Atoms.” <i>Physical Review Research</i>. American Physical Society, 2026. <a href="https://doi.org/10.1103/rdsn-stlq">https://doi.org/10.1103/rdsn-stlq</a>. Becker, A., et al. “Two-Body Kapitza-Dirac Scattering of One-Dimensional Ultracold Atoms.” <i>Physical Review Research</i>, vol. 8, 013297, American Physical Society, 2026, doi:<a href="https://doi.org/10.1103/rdsn-stlq">10.1103/rdsn-stlq</a>. Becker A, Koutentakis G, Schmelcher P. 2026. Two-body Kapitza-Dirac scattering of one-dimensional ultracold atoms. Physical Review Research. 8, 013297. A. Becker, G. Koutentakis, and P. Schmelcher, “Two-body Kapitza-Dirac scattering of one-dimensional ultracold atoms,” <i>Physical Review Research</i>, vol. 8. American Physical Society, 2026. Becker A, Koutentakis G, Schmelcher P. Two-body Kapitza-Dirac scattering of one-dimensional ultracold atoms. <i>Physical Review Research</i>. 2026;8. doi:<a href="https://doi.org/10.1103/rdsn-stlq">10.1103/rdsn-stlq</a> 216602026-04-05T22:01:32Z2026-04-07T09:37:57Z