Attaining the maximum Bose-Einstein condensation in a finite-size hard-core boson model

We propose a model for hard-core bosons in a lattice which allows to achieve the optimal occupation number predicted by Tennie et al (2017 Phys. Rev. B 96 064502) for a finite number of sites. The model is based on an extension of the Hamiltonian of the so-called Hubbard star, whose quantum properties are studied by means of quantum information descriptors such as the von Neumann entropy and the mutual information. These metrics are analyzed as a function of the one- and two-particle reduced density matrices, allowing to explore the relationship between condensation and entanglement by means of a control parameter that, under a given limit, connects our findings with previous results. All developments comprised in this article have been derived by analytical methods.