2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/89579In this paper, we give another proof of quantum Stein's lemma by calculating the information spectrum, and study an asymptotic optimal measurement in the sense of Stein's lemma. We propose a projection measurement characterized by the irreducible representation theory of the special linear group SL(H). Specially, in spin 1/2 system, it is realized by a simultaneous measurement of the total momentum and a momentum of a specified direction.LaTeX 12 pages The previous version has some typographic errorsQuantum Physicstext