Zakopane 2026 Conference on Nuclear Physics

We study the coupling between nuclear shape and rotation in even-even nuclei using a microscopic five-dimensional collective Hamiltonian based on relativistic density functional theory.

First, we identify wobbling motion—a precession of the total angular momentum about the medium axis—in triaxial nuclei such as ruthenium, palladium, and osmium. Using spin coherent state maps, we show that wobbling can also appear in γ-soft xenon isotopes, dynamically induced by the largest moment of inertia despite the absence of rigid triaxiality.

Second, we quantify shape-rotation entanglement via the von Neumann entropy. By comparing six representative nuclei, we reveal distinct entropy behaviors linked to triaxiality, γ-softness, and γ-rigidity. Along the hafnium isotopic chain, the entropy follows a three-stage evolution: it drops when prolate deformation stabilizes, stays flat under axial symmetry, and rises again when γ-softness and shape coexistence reappear. This entropy trend is linked to an experimentally measurable B(E2) ratio, making entanglement entropy a novel signature of nuclear shape evolution.

Overall, our work connects a specific collective wobbling mode to a general measure of quantum entanglement, offering new insights into shape-rotation coupling across the nuclear chart.