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I wanted to ask a question regarding the D0 detector in the original Scully and Yoon-Ho experiment (from 2000):

According to the paper itself, and to the wiki article:

"Note that the total pattern of all signal photons at D0, whose entangled idlers went to multiple different detectors, will never show interference regardless of what happens to the idler photons.[3] One can get an idea of how this works by looking carefully at both the graph of the subset of signal photons whose idlers went to detector D1 (fig. 3 in the paper[1]), and the graph of the subset of signal photons whose idlers went to detector D2 (fig. 4), and observing that the peaks of the first interference pattern line up with the troughs of the second and vice versa (noted in the paper as "a π phase shift between the two interference fringes"), so that the sum of the two will not show interference."

Now, suppose that the paths which the idler photons take are 1 light-year long, so that we can observe the pattern in D0 well before the idler photons are reach their detectors, and determine whether we'll find interference or not between them and their respective signal photons in D0.

Basically, my question is this -

From what I understand, all the photons that reached D0 have gone through a lense which erases their which-path data. So in a sense, if we only look at the path to D0, then we have a "regular" quantum eraser experiment!

In this case, why isn't there an interference pattern in D0???

Thanks in advance!

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# Question regarding the Delayed Choice Quantum Eraser expirement - interference at D0

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