Experimental detection of entanglement with optimal-witness families

Abstract

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.

Accepted for PRL. V3 includes an appendix which we comment on related work, discuss more general adaptive schemes, provide some technical details of the experiment. We thank the anonymous referees for critical suggestions and comments