Four-photon correction in two-photon Bell experiments V. Scarani, H. de Riedmatten, I. Marcikic, H. Zbinden and N. Gisin Eur. Phys. J. D, 32 1 (2005) 129-138 Published online: 30 November 2004 DOI: 10.1140/epjd/e2004-00170-7