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Here is the description of experiment which uses Mach–Zehnder interferometer


(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?

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I don't know too much about this experiment, but suffice to say that trying to understand this phenomenon intuitively will probably drive anyone insane! – Noldorin Nov 16 '10 at 0:04
It is not intuitive, at least not to me, so I agree. However I hope that there is a logical explanation, even the one which is not immediately graspable. – Art Nov 16 '10 at 0:28
What do you not understand? – Piotr Migdal Nov 16 '10 at 0:55
I complete Piotr's question : I see several possible points. Does the the problem with classical Mach-Zehnder interferometers ? Or in the fact that the classical interference apply also to single photons ? – Frédéric Grosshans Nov 16 '10 at 10:13

A very nice explanation here.

Don't forget:

When a light ray is incident on a surface and the material on the other side of the surface has a higher index of refraction... then the reflected light ray is shifted in its phase by exactly one half a wavelength.

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+1 good link. I think it would be even better if you summarize the argument of the linked page in your answer. – David Z Nov 16 '10 at 4:16
Uhm, I deliberately didn't want to do that because the info on the link is already summarized. If Art finds that explanation hard to understand, we can answer what he doesn't understand. By the way, according to, there are a lot of references explaining the experiment that are 'grossly misleading'. So better to be careful. – Robert Smith Nov 16 '10 at 4:48

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