2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/208061The feasibility of shell-model calculations is radically extended by the Quantum Monte Carlo Diagonalization method with various essential improvements. The major improvements are made in the sampling for the generation of shell-model basis vectors, and in the restoration of symmetries such as angular momentum and isospin. Consequently the level structure of low-lying states can be studied with realistic interactions. After testing this method on $^{24}$Mg, we present first results for energy levels and $E2$ properties of $^{64}$Ge, indicating its large and $γ$-soft deformation.12 pages, RevTex, 2 figures, to be published in Physical Review LettersNuclear Theorytext