Illustration of quantum complementarity using single photons interfering on a grating

A recent experiment performed by Afshar et al (2007 Found. Phys. 37 295-305) has been interpreted as a violation of Bohr's complementarity principle between interference visibility and which-path information (WPI) 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 WPI, characterized by the distinguishability parameter D, are found to obey the complementarity relation V 2 + D 2 6 1. This result demonstrates that the experiment can be perfectly explained by the standard interpretation of quantum mechanics.