Entropies and IPR as Markers for a Phase Transition in a Two-Level Model for Atom–Diatomic Molecule Coexistence Baena, Ignacio Pérez Fernández, Pedro Rodríguez Gallardo, Manuela Arias, José Miguel Quantum phase transitions Exactly solvable models Inverse participation ratio Rényi entropy This work is part of the I+D+i projects PID2019-104002GB-C22 and PID2020-114687GB-I00 funded by MCIN/AEI/10.13039/501100011033. This work is also part of grant Group FQM-160, EU FEDER funds US-1380840 and the project PAIDI 2020 with reference P20_01247, funded by the Consejería de Economía, Conocimiento, Empresas y Universidad, Junta de Andalucía (Spain) and “ERDF—A Way of Making Europe”. A quantum phase transition (QPT) in a simple model that describes the coexistence of atoms and diatomic molecules is studied. The model, which is briefly discussed, presents a second-order ground state phase transition in the thermodynamic (or large particle number) limit, changing from a molecular condensate in one phase to an equilibrium of diatomic molecules–atoms in coexistence in the other one. The usual markers for this phase transition are the ground state energy and the expected value of the number of atoms (alternatively, the number of molecules) in the ground state. In this work, other markers for the QPT, such as the inverse participation ratio (IPR), and particularly, the Rényi entropy, are analyzed and proposed as QPT markers. Both magnitudes present abrupt changes at the critical point of the QPT. 2022-02-10T12:20:03Z 2022-02-10T12:20:03Z 2022-01-12 info:eu-repo/semantics/article Baena, I.; Pérez-Fernández, P.; Rodríguez-Gallardo, M.; Arias, J.M. Entropies and IPR as Markers for a Phase Transition in a Two-Level Model for Atom–Diatomic Molecule Coexistence. Entropy 2022, 24, 113. [https://doi.org/10.3390/e24010113] http://hdl.handle.net/10481/72786 10.3390/e24010113 eng http://creativecommons.org/licenses/by/3.0/es/ info:eu-repo/semantics/openAccess Atribución 3.0 España MDPI