Relaño Pérez, ArmandoDukelsky, J.Pérez Fernández, P.Arias, J. M.2023-06-192023-06-192014-10-271539-375510.1103/PhysRevE.90.042139https://hdl.handle.net/20.500.14352/33842©2014 American Physical Society. This work is has been partially supported by the Spanish MINECO Grants No. FIS2012-35316, No. FIS2012-34479, and No. FIS2011-28738-c02-01, by Junta de Andalucía under group number FQM-160 and Project P11-FQM-7632, and by the Consolider-Ingenio 2010 Programme CPAN (CSD2007-00042).The ground state and spectral properties of Bose gases in double-well potentials are studied in two different scenarios: (i) an interacting atomic Bose gas, and (ii) a mixture of an atomic gas interacting with diatomic molecules. A ground state second-order quantum phase transition is observed in both scenarios. For large attractive values of the atom-atom interaction, the ground state is degenerate. For repulsive and small attractive interaction, the ground state is not degenerate and is well approximated by a boson coherent state. Both systems depict an excited state quantum phase transition. In both cases, a critical energy separates a region in which all the energy levels are degenerate in pairs, from another region in which there are no degeneracies. For the atomic system, the critical point displays a singularity in the density of states, whereas this behavior is largely smoothed for the mixed atom-molecule system.engjournal articlehttp://journals.aps.org/pre/abstract/10.1103/PhysRevE.90.042139http://journals.aps.org/open access536Double-well potentialQuantum phase transitionsTermodinámica2213 Termodinámica