Entangled photons in double slit experiment

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Discussion Overview

The discussion centers around the behavior of entangled photons in a double-slit experiment, specifically examining how the timing of detection for one photon (photon B) affects the interference pattern observed for another photon (photon A). The scope includes theoretical implications of quantum mechanics and the experimental setup involving entangled photons.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether setup 1 (photon B detected before photon A) will show an interference pattern while setup 2 (photon B detected after photon A) will not, due to the loss of wave function in photon B affecting photon A.
  • Another participant references existing research on the topic, indicating that similar experiments have been conducted.
  • Some participants argue that there is no difference in results due to the time ordering of the setups, suggesting both setups will yield the same outcome.
  • Concerns are raised about the complexities involved in demonstrating self-interference with entangled photons, noting that special conditions must be met.
  • Several participants express uncertainty about whether entangled photons can produce an interference pattern, with conflicting views suggesting it might be possible, impossible, or conditional on the setup.
  • One participant elaborates on the implications of entangled photons producing interference, discussing potential violations of quantum mechanics principles, such as faster-than-light (FTL) signaling and which-path information.
  • There is speculation that the degree of entanglement may influence the visibility of interference patterns, with more entanglement leading to increased noise in the results.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the effects of entanglement on interference patterns, and the discussion remains unresolved with no consensus reached on the outcomes of the different setups.

Contextual Notes

Participants note that the results are sensitive to specific experimental details and setups, which may not be fully defined in the discussion. The relationship between entanglement and interference patterns is complex and appears to depend on various conditions that are not universally agreed upon.

0xDEAD BEEF
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Hi,
imagine setup with source of entangled photons (A and B). Photon A travels to double slit so that either wave or particle pattern can be observed, photon B hits detector either before (setup 1) or after (setup 2) photon A has hit screen. Question:

Will setup 1 show interference pattern but setup 2 have it destroyed because photon B has lost its wave function (which should cause photon A to loose its wave function as well)?

Thnx,
Beefs
 
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There is no difference in the result due to time ordering. So the first setup will show the same result as the second setup.

Please note that these type setups are sensitive to a number of somewhat complicated details. You must jump through some special hoops to get entangled photons to evidence self-interference. Else there is no direct interference pattern.
 
DrChinese said:
You must jump through some special hoops to get entangled photons to evidence self-interference.

Woowaah, it is possible use entangled photons in a double-slit?? :bugeye:
 
DevilsAvocado said:
Woowaah, it is possible use entangled photons in a double-slit?? :bugeye:

No*

*Yes**

**Maybe.

The issue relates to the exact setup. Generally, we know plain ol' entangled ones don't make an interference pattern. If they did, you could either send FTL signals or determine which slit information. So assuming that can't happen, the explanation must be that you can't have interference when there is complete (in some sense?) entanglement.
 
DrChinese said:
No*

*Yes**

**Maybe.

:smile:

DrChinese said:
The issue relates to the exact setup. Generally, we know plain ol' entangled ones don't make an interference pattern. If they did, you could either send FTL signals or determine which slit information. So assuming that can't happen, the explanation must be that you can't have interference when there is complete (in some sense?) entanglement.

Yes, FTL seems to be the "ultimate barrier".

Ron Garret has a nice explanation why this must be (close to?) impossible:

  • If entangled photons do produce interference, we could use it to tell which-path in a double-slit, which is forbidden by QM.

  • If entangled photons do not produce interference, we could use it to send FTL signals, by utilizing a quantum eraser in one end (= interference in the other).
The answer to this "Catch-22" seems to be that a quantum eraser do indeed 'free' the other photon to produce interference, but this interference is a 'two-path-mixture' of interference patterns resulting in random noise, and the only way to filter out one path is by classical channels, i.e. exactly as in the 'ordinary' Delayed Choice Quantum Eraser.

So maybe the consequence of this is that; the more entanglement we have, for stricter which-path, the more noise we will have in a double-slit... and the less entanglement we have, for weaker which-path, the less noise we will have in a double-slit... or something like that...
 

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