2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/21948The decay of metastable states is dominated by quantum tunneling at low temperatures and by thermal activation at high temperatures. The escape rate of a particle out of a square well is calculated within a semi-classical approximation and exhibits an `ultrasharp' crossover: a kink in the decay rate separates a purely quantum regime at low temperatures from a purely thermal regime at high temperatures. An experimental system -- a quantum dot supplemented by a semiconductor heterostructure -- that may be used to check the prediction, along with necessary experimental conditions, are described.RevTeX, 4 pages, 3 eps figures insertedMesoscale and Nanoscale PhysicsStatistical Mechanicstext