Entanglement and symmetry effects in the transition to the Schroedinger cat regime

Abstract

We study two-spin entanglement and order parameter fluctuations as a function of the system size in the XY model in a transverse field and in the isotropic XXX model. Both models are characterized by the occurrence of ground state degeneracy also when systems of finite size are considered. This is always true for the XXX model, but only at the factorizing field for the XY model. We study the size dependence of symmetric states, which, in the presence of degeneracy, can be expanded as a linear combination of broken symmetry states. We show that, while the XY model looses its quantum superposition content exponentially with the size $N$, a decrease of the order of 1/N is observed when the XXX model is considered. The emergence of two qualitatively different regimes is directly related to the difference in the symmetry of the models.

References in corpus (7)

• Divergence of the entanglement range in low dimensional quantum systems
• Theory of ground state factorization in quantum cooperative systems
• Entanglement of finite cyclic chains at factorizing fields
• Two-spin entanglement distribution near factorized states
• Ground-state factorization and quantum phase transition in dimerized spin chains
• Reading entanglement in terms of spin configurations in quantum magnets
• Enhancement of pairwise entanglement from $\mathbbm{Z}_2$ symmetry breaking