Experimental detection of entanglement with optimal-witness families
  We report an experiment in which one determines, with least tomographic effort, whether an unknown two-photon polarization state is entangled or separable. The method measures whole families of optimal entanglement witnesses. We introduce adaptive measurement schemes that greatly speed up the entanglement detection. The experiments are performed on states of different ranks, and we find good agreement with results from computer simulations. 
Jibo Dai, Yink Loong Len, Yong Siah Teo, Berthold-Georg Englert, and   Leonid A. Krivitsky
quant-ph