article published yes Jinglun Li author ff19510a-0d2c-11ef-b018-c338ad2f4325 Paul S. Julienne author Johannes Hecker Denschlag author José P. D’Incao author MiLe department We derive an analog of the Lellouch-Lüscher (LL) relation for few-body bosonic systems, linking few-body scattering loss rates to the energies and widths of the corresponding harmonically trapped few-body states. Three-body numerical simulations show that the LL relation applies across a broad range of interaction strengths and energies and allows the determination of scattering rates within a single partial wave. Our Letter establishes a robust theoretical framework for understanding the role of the finite-volume effect in few-body observables in optical lattice and tweezer experiments, enabling precise determination of multibody scattering rates. https://research-explorer.ista.ac.at/download/22304/22330/2026_PhysicalReviewLetters_Li.pdf application/pdfno American Physical Society2026 eng 0031-9007 1079-7114 2511.1190610.1103/pzlp-7k8d 13620 Li, Jinglun, Paul S. Julienne, Johannes Hecker Denschlag, and José P. D’Incao. “Lellouch-Lüscher Relation for Ultracold Few-Atom Systems under Confinement.” <i>Physical Review Letters</i>. American Physical Society, 2026. <a href="https://doi.org/10.1103/pzlp-7k8d">https://doi.org/10.1103/pzlp-7k8d</a>. J. Li, P.S. Julienne, J.H. Denschlag, J.P. D’Incao, Physical Review Letters 136 (2026). Li, J., Julienne, P. S., Denschlag, J. H., &#38; D’Incao, J. P. (2026). Lellouch-Lüscher relation for ultracold few-atom systems under confinement. <i>Physical Review Letters</i>. American Physical Society. <a href="https://doi.org/10.1103/pzlp-7k8d">https://doi.org/10.1103/pzlp-7k8d</a> J. Li, P. S. Julienne, J. H. Denschlag, and J. P. D’Incao, “Lellouch-Lüscher relation for ultracold few-atom systems under confinement,” <i>Physical Review Letters</i>, vol. 136, no. 20. American Physical Society, 2026. Li J, Julienne PS, Denschlag JH, D’Incao JP. 2026. Lellouch-Lüscher relation for ultracold few-atom systems under confinement. Physical Review Letters. 136(20), 203401. Li J, Julienne PS, Denschlag JH, D’Incao JP. Lellouch-Lüscher relation for ultracold few-atom systems under confinement. <i>Physical Review Letters</i>. 2026;136(20). doi:<a href="https://doi.org/10.1103/pzlp-7k8d">10.1103/pzlp-7k8d</a> Li, Jinglun, et al. “Lellouch-Lüscher Relation for Ultracold Few-Atom Systems under Confinement.” <i>Physical Review Letters</i>, vol. 136, no. 20, 203401, American Physical Society, 2026, doi:<a href="https://doi.org/10.1103/pzlp-7k8d">10.1103/pzlp-7k8d</a>. 223042026-07-13T10:50:49Z2026-07-14T06:33:11Z