Nuclear pear-shaped, or octupole, deformation enhances the sensitivity of nuclei to fundamental symmetry-violating effects, including CP violation, yet its quantitative characterization, particularly its quantum fluctuations, remains challenging. We establish a multiscale validation strategy that combines low-energy electromagnetic transitions with intermediate-energy nucleus-nucleus collisions to probe octupole deformation and its associated quantum shape fluctuations. Using a microscopic collective Hamiltonian based on density functional theory, we first reproduce the electric octupole transition strengths of ${}^{226}\mathrm{Ra}, {}^{238}\mathrm{U}$, and ${}^{244}\mathrm{Pu}$, thereby validating the underlying nuclear-structure inputs. Within the isospin Boltzmann-Uehling-Uhlenbeck transport model, we then verify the geometric response by correlating initial participant eccentricities with self-correlation-subtracted two-particle flow observables. The resulting triangular-flow observable $v_3{\left\{2\right\}}^2$ scales with the mean-square octupole deformation $\langle {\beta }_3^2\rangle$. Crucially, the event-by-event fluctuation $\sigma \left[v_3{\left\{2\right\}}^2\right]$ exhibits a robust linear correlation with the octupole quantum-shape fluctuation $\sqrt{\langle {\beta }_3^4\rangle -{\langle {\beta }_3^2\rangle }^2}$. This provides an experimentally accessible collision observable for probing quantum fluctuations associated with nuclear deformation.

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• Low & intermediate energy heavy-ion reactions
• Nuclear reactions
• Nuclear shapes and moments
• Nuclear structure & decays
• A ≥ 220