Lellouch-Lüscher relation for ultracold few-atom systems under confinement Li, Jinglun Julienne, Paul S. Denschlag, Johannes Hecker D’Incao, José P. ddc:530 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. American Physical Society 2026 info:eu-repo/semantics/article doc-type:article article http://purl.org/coar/resource_type/c_2df8fbb1 https://research-explorer.ista.ac.at/record/22304 https://research-explorer.ista.ac.at/download/22304/22330 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> eng info:eu-repo/semantics/altIdentifier/doi/10.1103/pzlp-7k8d info:eu-repo/semantics/altIdentifier/issn/0031-9007 info:eu-repo/semantics/altIdentifier/e-issn/1079-7114 info:eu-repo/semantics/altIdentifier/arxiv/2511.11906 info:eu-repo/semantics/openAccess