Entanglement Observables and Witnesses for Interacting Quantum Spin   Systems
  We discuss the detection of entanglement in interacting quantum spin systems. First, thermodynamic Hamiltonian-based witnesses are computed for a general class of one-dimensional spin-1/2 models. Second, we introduce optimal bipartite entanglement observables. We show that a bipartite entanglement measure can generally be associated to a set of independent two-body spin observables whose expectation values can be used to witness entanglement. The number of necessary observables is ruled by the symmetries of the model. Illustrative examples are presented. 
L.-A. Wu, S. Bandyopadhyay, M.S. Sarandy, D.A. Lidar (Center for   Quantum Information and Quantum Control, University of To...