Mach-Zehnder Interferometer at Wiki Question

[daniel29208]

Can anyone help out?

I was reading about MZ interferometers on Wikipedia

http://en.wikipedia.org/wiki/Mach-Zehnder

In the wiki article they have a picture of 4 samples of photon paths in a MZ interferometer. They indicate the probability of a finding a photon at detectors (A,B,C) for 3 of the diagrams but the fourth they leave you guessing. I am really bugged. I can't find the answer anywhere. What is the probability of detecting a photon at detector A in the bottom right diagram. I am thinking it must be 50%?

 

[Ciokko]

where is the question? i think you misunderstood the article.
the top-left and bottom-left pictures represent the same apparatus, as well as the top-right and bottom-right.

 

[denian]

I can definitely help you out with this question! The answer to the probability of detecting a photon at detector A in the bottom right diagram is indeed 50%. This is because in a Mach-Zehnder interferometer, the light is split into two paths (upper and lower) and then recombined at the end. In the bottom right diagram, the light has been split and then recombined in such a way that there is an equal probability of the photon reaching detector A as there is of it reaching detector B. This is known as constructive interference, where the two paths have the same phase and therefore add up to a larger amplitude. Thus, the probability of detecting a photon at either detector A or B is equal, and since there are only two possible outcomes, the probability is 50%. I hope this helps clarify your understanding of MZ interferometers!