Here is the description of experiment which uses Mach–Zehnder interferometer
http://en.wikipedia.org/wiki/Mach-Zehnder
or
http://departments.colgate.edu/physics/research/Photon/root/ajpbs02.pdf
(see section "C. The experiments: The photon interferes with itself")
However I don't think I can fully understand the nature of what's happening in this experiment
Could possibly someone give an explanation preferably in simple terms or point to another source?
