Delayed Choice Quantum Eraser - double-photon explanation

[Cthugha]

Technically it is, but since there is a quite simple logical explanation to it, "delayed choice quantum eraser" sounds very misleading, doesn't it?

Does it? The original experiment was designed to ask clever questions about complementarity and does that very well. However, there were also people "selling" their papers who make it sound more spectacular than it really is, sure. The term "choice" is somewhat ill-chosen as the only choice of the experimentalist lies in which subset to pick. He does not actually change the outcomes after the detections happened as is claimed by some crackpot sites. Peer-reviewed papers never claimed that. At least not the papers I know.

And the reason you don't get the interference pattern on R₀₃ is not because the photons are distinguishable, but because there is simply no interference for those photons. Correct?

Is there a difference? The photon paths are distinguishable - there is only one way going to D3 after all. As you need two indistinguishable pathways to get interference there is of course also no interference. Interference and indistinguishability are so closely entwined that I would not det a dividing line there. You can even formulate a duality relation between distinguishability of photon paths and visibility of the resulting interference pattern called Englert-Greenberger duality relation. Imho, one of the more important results of DCQE is that it stresses the role of complementarity.

 

[zonde]

I never considered the pump photons behind BBO. Like I said before, I noticed that there are claims that the experiment equals to double-slit. If it does, the wave function won't collapse on BBO emission. To me it looked questionable, so I proposed an option of two photons hitting both A and B to later cause an interference on BS. It absolutely has nothing to do with the original beam.

If you would say that pump photon is in superposition of hitting region A and B ("superposition" is hitting region A and B ) it would be common QM terminology.

The way you said it sounds like explaining interference as two photons arriving at screen at the same time. This can be discussed but then it would be reasonable to base this discussion on simple double slit instead of DCQE.

Technically it is, but since there is a quite simple logical explanation to it, "delayed choice quantum eraser" sounds very misleading, doesn't it?
And the reason you don't get the interference pattern on R₀₃ is not because the photons are distinguishable, but because there is simply no interference for those photons. Correct?

In context of Cthugha's comment I would like to add that distinguishability can be trivial or rather nontrivial, for example, arrival time at the same detector.
As I understand your objection is that distinguishability is trivial in this case - only path A leads to R₀₃ and there is no way how path B can end up in that detector.

 

[San K]

just to make sure I got this right:

Does

"indistinguishablity of the various two-photon amplitudes"

means that

the paths are indistinguishable in the sense that either of the entangled photons could have took it and we cannot tell

i.e.

we cannot tell if photon A took path A or (its entangled twin) photon B took path A

same argument for path B

where path A and path B could, for example, be the upper arm or lower arm of the mach-zehnder

 

[zonde]

just to make sure I got this right:

Does

"indistinguishablity of the various two-photon amplitudes"

means that

the paths are indistinguishable in the sense that either of the entangled photons could have took it and we cannot tell

i.e.

we cannot tell if photon A took path A or (its entangled twin) photon B took path A

same argument for path B

where path A and path B could, for example, be the upper arm or lower arm of the mach-zehnder

The paths are indistinguishable in the sense that single photon could have taken either path to detection event.
For two-photon case it's when we can not tell apart from coincidence event case:
photon 1/path 1A & photon 2/path 2A
from case:
photon 1/path 1B & photon 2/path 2B