Illustration of quantum complementarity using single photons interfering   on a grating
  A recent experiment performed by S. S. Afshar et al. has been interpreted as a violation of Bohr's complementarity principle between interference visibility and which-path information in a two-path interferometer. We have reproduced this experiment, using true single-photon pulses propagating in a two-path wavefront- splitting interferometer realized with a Fresnel's biprism, and followed by a grating with adjustable transmitting slits. The measured values of interference visibility V and which-path information, characterized by the distinguishability parameter D, are found to obey the complementarity relation V^2+D^2=<1. This result demonstrates that the experiment can be perfectly explained by the Copenhagen interpretation of quantum mechanics. 
V. Jacques, N. D. Lai, A. Dreau, D. Zheng, D. Chauvat, F. Treussart,   P. Grangier, and J-F Roch