Puebla, RicardoRelaño Pérez, Armando2023-06-182023-06-182015-07-021539-375510.1103/PhysRevE.92.012101https://hdl.handle.net/20.500.14352/24129© 2015 American Physical Society. We thank O. Marty for useful discussions. The work was supported by a grant by the Spanish Government for research Project No. FIS2012-35316, an Alexander von Humboldt Professorship, the EU Integrating Project SIQS, and the EU STREP project EQUAM. Part of the calculations of this work were performed in the high-capacity cluster for physics, funded in part by Universidad Complutense de Madrid and in part with Feder funding. This is a contribution to the Campus of International Excellence of Moncloa, CEI Moncloa.For a certain class of isolated quantum systems, we report the existence of irreversible processes in which the energy is not dissipated. After a closed cycle in which the initial energy distribution is fully recovered, the expectation value of a symmetry-breaking observable changes from a value differing from zero in the initial state to zero in the final state. This entails the unavoidable loss of a certain amount of information and constitutes a source of irreversibility. We show that the von Neumann entropy of time-averaged equilibrium states increases in the same magnitude as a consequence of the process. We support this result by means of numerical calculations in an experimentally feasible system, the Lipkin-Meshkov-Glick model.engjournal articlehttp://dx.doi.org/10.1103/PhysRevE.92.012101http://journals.aps.org/open access536Quantum-systemsThermalizationEntropyTermodinámica2213 Termodinámica