Factorized ground states and field-driven entanglements switch in S=1/2 antiferromagnets

Full text: We study the field dependence of the entanglement of formation in anisotropic S=1/2 antiferromagnets displaying a T=0 field-driven quantum phase transition. The analysis is carried out via quantum Monte Carlo simulations. At zero temperature the entanglement estimators show abrupt changes at and around criticality, vanishing below the critical field, in correspondence with an exactly factorized state, and then immediately recovering a finite value upon passing through the quantum phase transition. At the quantum critical point, a deep minimum in the pairwise-t o-global entanglement ratio shows that multi-spin entanglement is strongly enhanced; moreover this signature represents a novel way of detecting the quantum phase transition of the system, relying entirely on entanglement estimators. Finally, our data at finite temperature indicate the possibility of realizing, by means of an external magnetic field, an entanglement switch, with the most welcome property of being temperature resistant. (author)