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Precise quantum tomography of photon pairs with entangled orbital angular momentum

Jack, B. and Leach, J. and Ritsch, H. and Barnett, S.M. and Padgett, M.J. and Franke-Arnold, S. (2009) Precise quantum tomography of photon pairs with entangled orbital angular momentum. New Journal of Physics, 11. ISSN 1367-2630

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Abstract

We report a high fidelity tomographic reconstruction of the quantum state of photon pairs generated by parametric down-conversion with orbital angular momentum (OAM) entanglement. Our tomography method allows us to estimate an upper and lower bound for the entanglement between the down-converted photons. We investigate the two-dimensional state subspace defined by the OAM states ± and superpositions thereof, with =1, 2, ..., 30. We find that the reconstructed density matrix, even for OAMs up to around =20, is close to that of a maximally entangled Bell state with a fidelity in the range between F=0.979 and F=0.814. This demonstrates that, although the single count-rate diminishes with increasing , entanglement persists in a large dimensional state space.