2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/89779A free quantum particle in two dimensions with vanishing angular momentum (s-wave) in the form of a ring-shaped wave packet feels an attractive force towards the center of the ring, leading first to an implosion followed by an explosion.4 pages, 1 PS figure, submitted to Phys. Rev. LettQuantum Physicstext