Measuring measurement

J.S. Lundeen , A. Feito, H. Coldenstrodt-Ronge , K.L. Pregnell , Ch. Silberhorn, T.C. Ralph, J. Eisert , M.B. Plenio, and I.A. Walmsley Clarendon Laboratory, Oxford University, Parks Road, Oxford, OX1 3PU, UK Institute for Mathematical Sciences, Imperial College London, SW7 2PE, UK QOLS, The Blackett Laboratory, Imperial College London, Prince Consort Rd., SW7 2BW, UK Max-Planck Research Group for Optics, Information and Photonics, Erlangen, Germany Department of Physics, University of Queensland, Brisbane, QLD 4072, Australia and Institute for Physics and Astronomy, University of Potsdam, 14476 Potsdam, Germany (Dated: July 15, 2008)