5/10/2007 Speaker: Paulo Henrique Souto Ribeiro Title: Experiments with entangled photons Abstract: We will discuss the production of twin photon pairs entangled in polarization, through the parametric down-conversion process, emphasizing the experimental aspects. We will also discuss some measurements schemes used to identify and quantify the entanglement of these states: violation of Bell inequalities, quantum state tomography and the approach using copies of states, that we have realized in our laboratory recently. Finally, we will talk about quantum key distribution using the transverse degree of freedom of the photons.