2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/125964We address the problem of the optimal quantum estimation of the coupling parameter of a bilinear interaction, such as the transmittivity of a beam splitter or the internal phase-shift of an interferometer. The optimal measurement scheme exhibits Heisenberg scaling of the measurement precision versus the total energy.Quantum Physicstext