Studying quantum spin systems through entanglement estimators

We study the field dependence of the entanglement of formation in anisotropic S=1/2 antiferromagneticchains displaying a T=0 field-driven quantum phase transition. The analysis is carried outvia quantum Monte Carlo simulations. At zero temperature the entanglement estimators show abruptchanges at and around criticality, vanishing below the critical field, in correspondence with an exactlyfactorized state, and then immediately recovering a finite value upon passing through the quantumphase transition. At the quantum-critical point, a deep minimum in the pairwise-to-global entanglementratio shows that multispin entanglement is strongly enhanced; moreover this signature represents anovel way of detecting the quantum phase transition of the system, relying entirely on entanglementestimators.