2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/224363We consider the Dicke Hamiltonian, a simple quantum-optical model which exhibits a zero-temperature quantum phase transition. We present numerical results demonstrating that at this transition the system changes from being quasi-integrable to quantum chaotic. By deriving an exact solution in the thermodynamic limit we relate this phenomenon to a localisation-delocalisation transition in which a macroscopic superposition is generated. We also describe the classical analogues of this behaviour.4 pages, 5 figures, minor changes, Journal ref. addedMesoscale and Nanoscale PhysicsDisordered Systems and Neural NetworksQuantum Physicstext