Quantitative entanglement witnesses of Isotropic- and Werner-class via   local measurements
  Quantitative entanglement witnesses allow one to bound the entanglement present in a system by acquiring a single expectation value. In this paper we analyze a special class of such observables which are associated with (generalized) Werner and Isotropic states. For them the optimal bounding functions can be easily derived by exploiting known results on twirling transformations. By focusing on an explicit local decomposition for these observables we then show how simple classical post-processing of the measured data can tighten the entanglement bounds. Quantum optics implementations based on hyper-entanglement generation schemes are analyzed. 
Pietro Silvi, Fabio Taddei, Rosario Fazio, Vittorio Giovannetti
quant-ph cond-mat.other physics.optics