2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/131617Given a single copy of a mixed state of the form ρ=λρ_1+(1-λ)ρ_2, what is the optimal measurement to estimate the parameter λ, if ρ_1 and ρ_2 are known? We present a general strategy to obtain the optimal measurements employing a Bayesian estimator. The measurements are chosen to minimize the deviation between the estimated- and the true value of λ. We explicitly determine the optimal measurements for a general two-dimensional system and for important higher dimensional cases.9 pages, 3 figures, v2: small changes, to appear in PRAQuantum Physicstext