Mach-Zehnder interferometer, but with an entangled beam?

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SUMMARY

The discussion centers on the application of the Mach-Zehnder interferometer using both a coherent light source and entangled photons. The experiment involves a 20 mW green laser diode at 532 nm for the coherent source and a violet pump laser diode at 405 nm to generate entangled photons via a BBO crystal. Participants debate whether the presence of an obstacle in one path will still allow Alice to observe interference patterns on her screens, concluding that Alice will not see interference fringes if entangled photons are used, regardless of whether one path is blocked.

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  • #31
Marilyn67 said:
1/ It seems that a beam of entangled particles carries a message ! This message is "I am entangled".
In other words, trying to create interference by all means without success, with a beam of which we don't know the source would be the signature of an entangled beam, right ?
Although the PDC source is a laser, the entangled beam that comes from the crystal lacks one attribute that is typical of laser light: coherence. Coherence is needed for the interference to appear. You *can* make the light be coherent, but then it will lose some of its entangled properties. To the extent you get more of one attribute, you get less of the other.
 
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  • #32
Hello @DrChinese ,

Thank you for your quick response.

Something escapes me:

In 1803, Thomas Young performed his experiment of the two slits with a beam of sunlight and found interference.
A reproduction of the experiment can be seen here as well as the reading of Thomas Young's manuscripts :



I thought sunlight wasn't coherent light, like from an incandescent bulb ?

Cordially,
Marilyn
 
  • #34
Thank you @DrClaude, this discussion is indeed very interesting ! :smile:
 

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