Quantum entanglement with acousto-optic modulators: 2-photon beatings   and Bell experiments with moving beamsplitters
  We present an experiment testing quantum correlations with frequency shifted photons. We test Bell inequality with 2-photon interferometry where we replace the beamsplitters by acousto-optic modulators, which are equivalent to moving beamsplitters. We measure the 2-photon beatings induced by the frequency shifts, and we propose a cryptographic scheme in relation. Finally, setting the experiment in a relativistic configuration, we demonstrate that the quantum correlations are not only independent of the distance but also of the time ordering between the two single-photon measurements. 
Andre Stefanov, Hugo Zbinden, Antoine Suarez, and Nicolas Gisin