Quantitative entanglement witnesses of isotropic and Werner classes 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. Their 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. © 2011 IOP Publishing Ltd.