Entanglement - lack of "symmetry" in no-hidden variables explanation

[PeterDonis]

Moderator's note: I have deleted some posts (of mine) that are incorrect or misleading in the light of further discussion.

 

[DrChinese]

Would this mean the photons aren't entangled? Or just that nothing comes out at all?

Sometimes there is only 1 photon (in the 0 & 3 channels) rather than two within the required time window. So there is one in the 0 channel but none in the 3 channel, or vice versa. That is because you are actually looking at the 1 & 2 channels, and one of those is missing a photon within the time window. There must be both a 1 & 2 that are indistinguishable for the 0 & 3 to be primed and ready. Keep in mind that the 0 & 1 is one source, 2 & 3 is a separate source, and there is no requirement that they create pairs at exactly the same time. Only occasionally does that happen, and in fact most of the time there is nothing present.

 

[EPR]

Just to add to what others have already said: You can entangled objects that have never been in contact. One way to do it is called "entanglement swapping".

https://arxiv.org/abs/quant-ph/0201134

But their partners interacted locally widening the entanglements to the other 2 co-entangled partners nonlocally. How is this unexpected? Everything is entangled all the time.

 

[EPR]

Isn't ubiquitous entanglement breaking the only explanation why we observe a seemingly 'classical' reality arise from an infinitely entangled quantum world upon observation/interaction?

 

[Demystifier]

I wonder if the OP means time symmetrical.

Can you (in principle) reverse the process, and have a pair of unentangled particles at a distance become entangled?

The Schrödinger equation contains such solutions, so in principle yes.

 

[vanhees71]

Ok, so this would be a "yes" answer to my question. In that case, yes, you're right, I need to re-evaluate my understanding. I'll take more time to read the references you provided when I can (and probably follow up with further papers referenced in those).
Would this mean the photons aren't entangled? Or just that nothing comes out at all?

No, you don't. In the entanglement-swapping experiment by Zeilinger et al. the entanglement of 0&3 is only established if you choose a subensemble based on a measurement on 1&2. You can do this after all experiments are done using the meausurement protocols of the various local measurements, and there are only local measurements in this experiment. At least there's nothing in this experiment which hints at any violation of QED, which is local. There's no need to assume any action at a distance at all. The correlations due to entanglement are there due to the preparation procedure. Of course 0&3 have never been in local contact and they are entangled if you choose the wanted subensemble based on measurments of 1&2, but this doesn't imply any non-local interactions.

 

[vanhees71]

Your requirement about the destructive measurements does not in any way invalidate (or even apply) to my position. But regardless, here is a version where entangled photons are created without interacting and no destructive measurement occurs.

https://arxiv.org/abs/quant-ph/0609135
Non-local generation of entanglement of photons which do not meet each other (2006)
Note that in this one, there are just 2 photons that are entangled without meeting each other - there is no swap operation at all.

Is this somewhere published in readable form?

 

[DrChinese]

But their partners interacted locally widening the entanglements to the other 2 co-entangled partners nonlocally. How is this unexpected?

Because 2 remote photons take on a new physical relationship as a result. Their entangled partner changes from one photon to another. If you think that isn't "unexpected", that's your take and it certainly follows QM.

 

[DrChinese]

At least there's nothing in this experiment which hints at any violation of QED, which is local. There's no need to assume any action at a distance at all. The correlations due to entanglement are there due to the preparation procedure. Of course 0&3 have never been in local contact and they are entangled if you choose the wanted subensemble based on measurments of 1&2, but this doesn't imply any non-local interactions.

Quit saying things that are exactly opposite of what virtually every reference says. I don't mean to be rude or combative, but this has got to stop. Simply put: put up or shut up. I am tired of you making leaps that are unfounded. I have provided the forum required references over and over. You have yet to provide one. My references say that quantum teleportation is a non-local operation, just read the titles of 5 papers from the top teams in the field.

Long distance entanglement swapping with photons from separated sources
Entanglement Between Photons that have Never Coexisted
Experimental Nonlocality Proof of Quantum Teleportation and Entanglement Swapping
Non-local generation of entanglement of photons which do not meet each other
Characterizing the nonlocal correlations of particles that never interacted

I don't know how you get by without providing references to your personal opinions when challenged - so in fact I will report you and let PeterDonis or another mentor sort it out. But I will not further discuss with you in this thread unless you do.

 

[EPR]

I think you two misunderstand each other because of a curious phenomenon - namely the working physicist's mindset - to not believe in nonlocal influences. They would tacitly get rid of realism just so that they can do local physics.
When Vanhees71 says 'this doesn't imply nonlocal interaction' he likely means the 4 entangled photons/electrons are one quantum system(until measurement). You just word the same setup differently.
I can agree that there are no nonlocal interactions. It's a valid way to look at the experiment.

 

[Lord Jestocost]

I, personally, would prefer to avoid the term “non-locality” within such discussions as some connote it immediately with “non-local interactions” or “action at a distance” etc..
It would be better to use the term “quantum non-separability” which can be stated as “even when two regions of space are disconnected and very far apart, one cannot always attribute separate physical properties to what they contain" (Franck Laloë).

 

[EPR]

Imagine being a physicist and your calculations had to include instantaneous influences across the Universe.
To most physicists realism has been dead for decades(though they would seldom express it as confidently as i do, they implicitly assume it in nearly every second post here).

 

[EPR]

PeroK, do you believe particles have definite positions and momenta before interaction/measurement? I seldomly see physicists supporting such a notion(usually die-hard BM fans and HV proponents).

 

[PeroK]

PeroK, do you believe particles have definite positions and momenta before interaction/measurement? I seldomly see physicists supporting such a notion(usually die-hard BM fans and HV proponents).

I tend towards orthodox QM, at least insofar as I need an interpretation to explain things. So, no. Orthodox QM is clear on this. That's one of the reasons I questioned the notion of the two particles being in "the same place at same time".

 

[PeterDonis]

Thread closed for moderation.