Quantum entanglement communication

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Discussion Overview

The discussion revolves around the concept of quantum entanglement and its implications for communication, particularly in relation to the delayed choice quantum eraser experiment. Participants explore whether it is possible to communicate information faster than light using entangled particles and the conditions under which interference patterns are observed.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant questions if a signal can be communicated faster than light by using entangled particles, suggesting a scenario where Bob informs Alice to take action based on the state of his particle.
  • Another participant reflects on their initial question, concluding that while the mechanism seems to work, it does not allow for faster-than-light communication due to the necessity of prior communication between Bob and Alice.
  • A participant points out that entangled particles do not produce interference patterns in the same way as single particles do, referencing a specific source for clarification.
  • Confusion arises regarding the nature of interference patterns in delayed choice quantum eraser experiments, with a participant questioning the validity of the experiment's results.
  • Participants differentiate between two types of delayed choice experiments: Type I, which involves a single particle without entanglement, and Type II, which involves two entangled particles and requires joint measurements to observe interference.
  • A novice participant inquires about the effects of removing certain components from the quantum eraser experiment on the resulting interference pattern.

Areas of Agreement / Disagreement

Participants express differing views on the implications of quantum entanglement for communication and the interpretation of interference patterns in delayed choice experiments. There is no consensus on the ability to communicate faster than light or the correctness of the experimental interpretations.

Contextual Notes

Participants highlight the complexity of the experiments and the need for careful consideration of the definitions and conditions involved in quantum mechanics. The discussion reflects uncertainty regarding the outcomes of specific experimental modifications.

Who May Find This Useful

This discussion may be of interest to those exploring quantum mechanics, particularly in relation to quantum entanglement, communication theories, and the nuances of delayed choice experiments.

idea2000
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Hi,

I've been reading some stuff about quantum entanglement and I stumbled upon an article talking about a delayed choice quantum eraser experiment using parametric down conversion. I was wondering if it was possible to communicate a signal through to the other side faster than light. I know that you can't send any information over the channel to the other side faster than light because you don't know which side picked which state, but what if all I'm interested in is that the other side picked any state?

For example, if Alice is in one room while Bob is in another. Bob tells Alice, "As soon as I force my particle to pick a state, take the clothes to the dry cleaners." In his room, Bob forces his particle to pick a state, while Alice is observing the interference pattern from her photons in her room. As soon as Alice's interference pattern disappears, she knows she's supposed to take the clothes out to the dry cleaners. Now, if Alice was in a different galaxy than Bob, wouldn't Bob have communicated to her to take the clothes to the dry cleaners faster than light?
 
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I think I might have answered my own question.

In my example above, the mechanism that I'm suggesting to communicate does work, but it's just that it's actually not faster than light. And the reason is because Bob has to first tell Alice what to do and then go to the other galaxy at slower than light speed. Can I verify that this is correct?
 
idea2000 said:
For example, if Alice is in one room while Bob is in another. Bob tells Alice, "As soon as I force my particle to pick a state, take the clothes to the dry cleaners." In his room, Bob forces his particle to pick a state, while Alice is observing the interference pattern from her photons in her room. As soon as Alice's interference pattern disappears, she knows she's supposed to take the clothes out to the dry cleaners. Now, if Alice was in a different galaxy than Bob, wouldn't Bob have communicated to her to take the clothes to the dry cleaners faster than light?

Surprisingly, entangled particles do not produce such interference. See for example:

Experiment and the foundations of quantum physics, Anton Zeilinger, p. 290, Figure 2.
http://www.hep.yorku.ca/menary/courses/phys2040/misc/foundations.pdf

So that is issue number 1 here.
 
The confusion stems from the fact that there are TWO types of delayed choice experiments.

Type I involves only one interfering particle, there is no other particle entangled with it. The interference pattern can be seen on the screen, but there is nothing superluminal about it because there is no entanglement.

Type II involves two entangled particles, where one of them impinges on the screen. The interference pattern is not seen on the screen. Interference is only seen in coincidences through joint measurements of BOTH particles.
 
Hi,

Thanks for your replies. =) I'm a novice at this stuff, so thanks for your patience. I was wondering, if you take away D3 and D4 and also remove Bsa and Bsb in the quantum eraser experiment in the wikipedia article, would you still get an interference pattern? Thanks in advance for any help you can give. =)

http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser
 

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