Non-local preparation in entanglement swapping experiments

[DrChinese]

I don't have enough knowledge to answer [whether the 1 & 4 particles interacted in any way]... but after reading this thread and the one on interpretations of quantum mechanics I needed that answer to understand the conversation that is being held here. (I can't find the explicit answer in the papers)

Perhaps I can help, at least discussing the cases of whether the 1&4 or 2&3 photons interact in any way. This is the 2012 paper by Zeilinger's team, in which the 2 & 3 interaction variable is the primary objective of the paper - and no interaction between 1 & 4.
Φ

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Re: 1&4 photons interacting:

In no cases do the 1 & 4 photons ever interact. They are created at separate locations (different PDC crystals) about .5 meter apart and fed into fiber, and measured about 35ns later. There is no time or place for them to interact. From Figure 2 of the paper:

"Photons 1 and 4 are directly subject to the polarization measurements performed by Alice and Bob (green blocks".

In other experiments, the separation of photons 1 and 4 are more clearly delineated than in this particular experiment. But obviously: If the independent variable is what happens at the BSM, then any hypothetical interaction can't really matter to our conclusion.

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Re: 2&3 photons interacting:

1. To execute a swap via the BSM, the 2 & 3 photons must arrive at the beam splitter within a narrow time window. The same time window is applied whether an Entangled State (ES) measurement is to result, or a Separable (non-entangled) State (SS) measurement is to occur. The decision to make it ES or SS is made randomly by automation on a case by case basis. The time window is measured by clicks at the BSM in 2 detectors.

2. There are 4 possible Bell states that result from a entanglement swap. For a variety of mostly technical reasons, only a single state is reported in the experiment. That is the |φ-> state. That state is indicated when the BSM registers either two H clicks or two V clicks at the BSM. Note that to get the two clicks |HH> or |VV>, that can result only from the 2 & 3 photons being both reflected or both transmitted at the beam splitter (BS). The only entangled stats being reported are from this one Bell state for ES scenario. No other Bell states are being combined with the entangled |Φ-> state numbers. Similarly, the SS scenario also looks at |HH> or |VV> results at the BSM. So the statistics are "apples to apples". The key here is that we are going to compare the ES and SS (entangled vs non-entangled) correlations. From the paper:

"After all the data had been taken, we calculated the polarization correlation function of photons 1 and 4. It is derived from their coincidence counts of photons 1 and 4 conditional on projecting photons 2 and 3 to |Φ−〉23 = (|𝐻𝐻〉23 − |𝑉𝑉〉23)/√2 when the Bell-state measurement was performed, and to |𝐻𝐻〉23 or |𝑉𝑉〉23 when the separable state measurement was performed."

3. Here is exactly how the physical variable changes that creates the ES (entangled) or SS (non-entangled) results: There are 2 Electro-Optical Modulator (EOM 1 and EOM 2, see figure 2) that together change the beam splitter between 2 possible configurations. To get ES outcomes, the beam splitter operates in a 50:50 mode - that is, 50% transmitted and 50% reflected. To get SS outcomes, the beam splitter operates in a 0:100 mode - that is, 0% transmitted and 100% reflected (i.e. a mirror).

There IS entanglement when the 2 & 3 photons can overlap in the beam splitter within the time window, but you cannot know whether both photons were transmitted - or both were reflected (50:50). I.e. the 2 & 3 photons are indistinguishable. There is NO entanglement when the 2 & 3 photons cannot overlap in the beam splitter within the time window, because both were reflected (0:100) before they could possibly cross. I.e. now the 2 & 3 photons are easily distinguishable according to which side's detectors click.

This is the only difference between the statistics reported in Figure 3 between the a) side [left 3 bars] and the b) side [right 3 bars]. The easiest to see is the middle of the 3 bars on each side. These are the associated click outcomes for the |RR>/|LL> correlations at the Alice and Bob stations. The middle bars have the Alice and Bob stations only measuring circular polarization R or L. When there is |Φ-> entanglement, Alice and Bob should get identical results on any same basis, so you would expect mostly RR> or LL> outcomes and few LR> or RL> outcomes. Without entanglement, Alice and Bob should not see any correlation. Note that correlation is calculated as C=(Matches - Mismatches)/(Matches + Mismatches) and can vary from 1 to -1.

When the Entangled State was selected randomly, you expect significant correlation (theoretically perfect would be C=1.0). When the Separable State was selected, you expect no significant correlation (theoretically perfect would be C=0.0).

The actual entangled (ES) correlation is about 0.603+/-0.071, while the actual separable (SS) correlation is about 0.010+/-0.072. These results are clearly saying: If a physical change is made at the BSM, then there is a corresponding observable change of the overall statistics - as predicted by QM.

So the answer is: When there is an entanglement swap, the 2&3 photons are allowed to physically interact (but they aren't if a separable state is to be generated). The only thing varied in the results a) vs b) is that setup at the BSM. So the difference in statistics, according to norms in experimental science, is the independent variable. Which is selected and chosen well after the Alice and Bob perform their measurements on photons 1 & 4.

You can make of this what you like.

 

[DrChinese]

If you insist that they are entangled what is the state of the system 1&4?

ps What do you call Einstein causality?

In the 2012 Ma experiment, the 1 & 4 system is |Φ-> for all the reported cases in Figure 3a). For the reported Separable State cases in 3b), they are either |HH> or |VV> which of course is not entangled.

Einsteinian causality requires causes to occur before effects, with limits of propagation through spacetime of cause to effect not to exceed c. Obviously, the predictions of QM do not satisfy this condition. This has been known for a long time, as a future nonlocal context is the sole factor/determinant for the quantum expectation value in many scenarios. For example, the well known cos^2(theta) function for entanglement matches.

 

[DrChinese]

I read it. I am quoting it! They say that the set of measurments on 1&4 shows no correlation. Only the subset for those trials on which Victor obtained a one of the possible outcomes of his measurment.

You failed to quote anything that you actually interpreted correctly. Yes, measurements on photons 1 & 4 alone show no correlation in these experiments UNLESS there is a specific outcome at the BSM - AND there is interaction (interference) between 2 & 3 at the BSM as well.

Please read my #36 above which explains everything in detail. Please note again the independent variable in this scientific experiment.

 

[PeterDonis]

If you insist that they are entangled what is the state of the system 1&4?

In the interpretation @DrChinese is using, where the quantum state describes individual runs of the experiment, the state of the system 1&4 for each individual run is the appropriate Bell state induced by the swap operation on 2&3 for that run.

In a statistical interpretation, the state you assign depends on what subset of runs you are doing statistics on. If you take the entire set of runs, without picking out any subsets, then the state of 1&4 is the appropriate mixed density matrix that shows no correlations. If you pick out subsets of runs corresponding to particular outputs of the swap operation on 2&3, then the state of 1&4 for those subsets is the corresponding Bell state, as above.

What you can't do is take the entire set of runs, point out that that set shows no correlation between 1&4, and then use that as a basis for an assertion that 1&4 are not entangled in individual runs. The "no correlation" statistics are only relevant for a statistical interpretation. On an interpretation that assigns quantum states to individual runs, there is no such thing as "no correlation"; every run (or more precisely every run where a swap takes place, but that's sufficient for this discussion) puts 1&4 into some definite Bell state. There are no runs where a swap takes place but there is no correlation between 1&4.

In other words, as far as I can tell, you and @DrChinese are talking past each other because you are using different, incompatible interpretations.

 

[martinbn]

In the interpretation @DrChinese is using, where the quantum state describes individual runs of the experiment, the state of the system 1&4 for each individual run is the appropriate Bell state induced by the swap operation on 2&3 for that run.

In a statistical interpretation, the state you assign depends on what subset of runs you are doing statistics on. If you take the entire set of runs, without picking out any subsets, then the state of 1&4 is the appropriate mixed density matrix that shows no correlations. If you pick out subsets of runs corresponding to particular outputs of the swap operation on 2&3, then the state of 1&4 for those subsets is the corresponding Bell state, as above.

What you can't do is take the entire set of runs, point out that that set shows no correlation between 1&4, and then use that as a basis for an assertion that 1&4 are not entangled in individual runs. The "no correlation" statistics are only relevant for a statistical interpretation. On an interpretation that assigns quantum states to individual runs, there is no such thing as "no correlation"; every run (or more precisely every run where a swap takes place, but that's sufficient for this discussion) puts 1&4 into some definite Bell state. There are no runs where a swap takes place but there is no correlation between 1&4.

In other words, as far as I can tell, you and @DrChinese are talking past each other because you are using different, incompatible interpretations.

My question about the state meant to point out that it makes no sense to talk about it since they have never coexisted. If 1&4 have never coexisted what does it mean to be in a given state!

If @DrChinese is using an interpretation, then i have no problem with his claims. But it seems to me that he insists that his discription is the only posssible one.

 

[pines-demon]

My question about the state meant to point out that it makes no sense to talk about it since they have never coexisted. If 1&4 have never coexisted what does it mean to be in a given state!

Even if two particles have never interacted you can write their state quantum mechanically. In the case of entanglement swapping, the math of QM tells us how to write the state.

 

[martinbn]

Even if two particles have never interacted you can write their state quantum mechanically. In the case of entanglement swapping, the math of QM tells us how to write the state.

I am not talking about particles that haven't interacted, but about particles that haven't coexisted. If you have a photon that was emitted and absorbed a year ago and another that was emitted and absorbed today, does it make sense to talk about the state of the two photon system?

 

[pines-demon]

I am not talking about particles that haven't interacted, but about particles that haven't coexisted. If you have a photon that was emitted and absorbed a year ago and another that was emitted and absorbed today, does it make sense to talk about the state of the two photon system?

I might need to check this with spacetime plots, but if two worldlines that are not casually tied can't you just find a reference frame where both are simultaneous?

 

[DrChinese]

If @DrChinese is using an interpretation, then i have no problem with his claims. But it seems to me that he insists that his discription is the only posssible one.

My “interpretation” is just standard QM, I.e. the predictions thereof. It predicts perfect correlation in certain situations, in principle with each and every run. But limitations in real world experiments do not achieve that.

The combination of the theoretical predictions and the actual results lead to some clear descriptions. However, there are multiple alternative ways to describe the situation too. My point is simply that one should start at one spot (obvious signs of nonlocality) first. But each person is free to start where they like.

Some hold Einsteinian causality higher than QM, for example. I would say these each have their own domain of application, neither supercedes the other.

 

[DrChinese]

I am not talking about particles that haven't interacted, but about particles that haven't coexisted. If you have a photon that was emitted and absorbed a year ago and another that was emitted and absorbed today, does it make sense to talk about the state of the two photon system?

And yet such 2 photon state has been so described, and has been produced experimentally. Publication: Phys. Rev. Lett. 110, 210403 (2013), so hopefully not too much to question here.

Entanglement Between Photons that have Never Coexisted

"According to this description, the timing of each photon is merely an additional label to discriminate between the different photons, and the time in which each photon is measured has no effect on the final outcome. The first photon from the first pair (photon 1) is measured even before the second pair is created (see Fig. 1). After the creation of the second pair, the Bell projection occurs and only after another delay period is the last photon from the second pair (photon 4) detected. Entanglement swapping creates correlations between the first and last photons non-locally not only in space, but also in time. ...

"In conclusion, we have demonstrated quantum entanglement between two photons that do not share coexistence. Although one photon is measured even before the other is created, full quantum correlations were observed by measuring the density matrix of the two photons, conditioned on the result of the projecting measurement [into Bell states |φ+> or |φ−>]. This is a manifestation of the non-locality of quantum mechanics not only in space, but also in time."

 

[DrChinese]

I might need to check this with spacetime plots, but if two worldlines that are not casually tied can't you just find a reference frame where both are simultaneous?

It is not true that 2 distant events in spacetime A & B must necessarily demonstrate some reference frame in which order is reversed. It is dependent on the distance between them in both space and time.

Suppose A and B start with synchronized clocks. At T=0, A makes her measurement. At T=3 nanoseconds, B makes his measurement. If A and B are separated by less than a meter (approximately), there is no reference frame (accelerated or not) in which B appears to occur before A.

I am not so well versed in Special Relativity regarding accelerated reference frames. If I am incorrect, please set me on the right path.

 

[Morbert]

My “interpretation” is just standard QM, I.e. the predictions thereof. It predicts perfect correlation in certain situations, in principle with each and every run. But limitations in real world experiments do not achieve that.

The correlations predicted by QM are not disputed. What's disputed is their significance re/ nonlocal influence. It is my position - and Peres's, Fuchs's, Brun's, Griffiths's et al - that ordinary QM doesn't necessarily imply nonlocal influence.

And yet such 2 photon state has been so described, and has been produced experimentally. Publication: Phys. Rev. Lett. 110, 210403 (2013), so hopefully not too much to question here.

Entanglement Between Photons that have Never Coexisted

"Entanglement swapping creates correlations between the first and last photons non-locally not only in space, but also in time. ...

Similarly, what these experiments show is that we can induce Bell-inequality-violating correlations between outcomes of measurements on photons that never coexisted, but we can give accounts of these correlations without recourse to nonlocal influence.

 

[pines-demon]

It is not true that 2 distant events in spacetime A & B must necessarily demonstrate some reference frame in which order is reversed. It is dependent on the distance between them in both space and time.

Suppose A and B start with synchronized clocks. At T=0, A makes her measurement. At T=3 nanoseconds, B makes his measurement. If A and B are separated by less than a meter (approximately), there is no reference frame (accelerated or not) in which B appears to occur before A.

I am not so well versed in Special Relativity regarding accelerated reference frames. If I am incorrect, please set me on the right path.

Nevermind reversing the order, if two events are not connected causally (space-like separated) you can always find a non-accelerated frame when you can treat the two events as if the events started at the same time.

 

[pines-demon]

The correlations predicted by QM are not disputed. What's disputed is their significance re/ nonlocal influence. It is my position - and Peres's, Fuchs's, Brun's, Griffiths's et al - that ordinary QM doesn't necessarily imply nonlocal influence.

What do these authors propose to interpret the entanglement correlations?

Similarly, what these experiments show is that we can induce Bell-inequality-violating correlations between outcomes of measurements on photons that never coexisted, but we can give accounts of these correlations without recourse to nonlocal influence.

Coexistence does not matter much if you use nonlocal interactions...

 

[DrChinese]

Nevermind reversing the order, if two events are not connected causally (space-like separated) you can always find a non-accelerated frame when you can treat the two events as if the events started at the same time.

If you can’t flip the order in some reference frame, they cannot be made to look simultaneous either.

It’s a question of distance apart in spacetime. I gave you a specific example. Why don’t you address that one, and show some reference frame where the A and B events are simultaneous?

 

[DrChinese]

The correlations predicted by QM are not disputed. …what these experiments show is that we can induce Bell-inequality-violating correlations between outcomes of measurements on photons that never coexisted, but we can give accounts of these correlations without recourse to nonlocal influence.

I hear of the existence of these “accounts”. And I literally have a hundred+ bookmarks for various ones making similar claims. I cannot find anything at all that actually* maintains strict local/Einsteinian causality.

Local information transfer/update to explain remote delayed choice swapping? Basically, that’s a straight out violation of Bell’s Theorem.


*They gotta explain swapping without hand-waving. Nonlocal influences will do the trick of course. But even those need boundaries.

 

[PeterDonis]

If you have a photon that was emitted and absorbed a year ago and another that was emitted and absorbed today, does it make sense to talk about the state of the two photon system?

I think the answer is yes (but see my question below)--or more precisely yes for the state of the overall 4 photon system in the entanglement swapping experiment. The usual formulation of NRQM doesn't cover such cases, but I think QFT can. If the two photons you describe are photons 1&4 in an entanglement swapping experiment (which is possible in principle, though still well beyond our practical capabilities), then I think you can pick out appropriate spacetime events and appropriate quantum field operators to describe the experiment and the 4 photon system that it is an experiment on. In QFT a "state" does not have to be a state at a particular time. I think any combination of QFT degrees of freedom can in principle describe a "state", though of course the vast majority of such combinations have no practical use.

That does raise a question, though: @DrChinese, do you know of any reference that develops the kind of formulation I just described, that can cover an entanglement swapping experiment of the kind @martinbn described? I'm curious as to how much of what I just hand-waved has actually been rigorously investigated.

[Edit--I see the reference @DrChinese gave in post #45, I'll take a look.]

 

[PeterDonis]

if two events are not connected causally (space-like separated)

In the case @martinbn described, the events of photon 1 being emitted and absorbed could be in the past light cone of the events of photon 1 being emitted and absorbed. But it's true that they wouldn't have to be; it would be possible to set things up so those events were spacelike separated (though expensive, since you'd have to have a lab at least a light year wide).

 

[Morbert]

What do these authors propose to interpret the entanglement correlations?

Fuchs and Peres read QM as a theory of macroscopic tests and preparations, and not as a realistic theory of the microscopic. They maintain that nonlocal influence is necessary to postulate only when attempting to reproduce QM with a realistic theory of the microscopic. Entanglement is a characteristic of states, and hence they interpret it as a characteristic of preparations, giving rise to Bell-inequality-violating correlations under the right tests.

Brun and Griffiths read QM as a realistic theory, but introduce a restriction on the construction of logical propositions about quantum systems. They argue that this restriction eliminates the need to infer nonlocal influence. https://arxiv.org/abs/0908.2914

Note that none of these approaches premise "no nonlocal influence" on coincident pasts of subsystems. As such, papers like the one referenced by @DrChinese in post #45 don't pose a novel challenge to these approaches.

 

[DrChinese]

That does raise a question, though: @DrChinese, do you know of any reference that develops the kind of formulation I just described, that can cover an entanglement swapping experiment of the kind @martinbn described? I'm curious as to how much of what I just hand-waved has actually been rigorously investigated.

[Edit--I see the reference @DrChinese gave in post #45, I'll take a look.]

A couple of additional comments. Obviously, there are some limits to the amount of separation that can be achieved on the planet Earth*. There have been a number of experiments where the swaps are separated by larger distances than the one I referenced previously. That one was only about 1 meter. This one is a much larger distance:

Field test of entanglement swapping over 100-km optical fiber with independent 1-GHz-clock sequential time-bin entangled photon-pair sources

Depending on how you calculate the distance between Alice and Bob, they are either 12.5 km apart (physical distance) or about 65 km apart (virtual distance including coiled fiber, my best estimate). In this particular experimental setup, the relative times and ordering can be adjusted arbitrarily. I was unable to deduce what the experimenters' actual timing was for this paper.

There have also been earth-to-satellite tests, but I don't think those citations would add much.


*A millisecond translates to 300 km of distance at c.

 

[DrChinese]

Brun and Griffiths read QM as a realistic theory, but introduce a restriction on the construction of logical propositions about quantum systems. They argue that this restriction eliminates the need to infer nonlocal influence. https://arxiv.org/abs/0908.2914

Note that none of these approaches premise "no nonlocal influence" on coincident pasts of subsystems. As such, papers like the one referenced by @DrChinese in post #45 don't pose a novel challenge to these approaches.

I both agree and disagree with the Griffiths citation in various manners.

1. First, I criticize him for specifically ignoring GHZ, swapping and other theorems/experiments. "In an article of modest length it is impossible to deal with all published arguments claiming that quantum theory is beset with nonlocal influences and in conflict with special relativity. In particular we do not discuss those based upon the GHZ [60, 61] or Hardy [62] paradoxes, nor Stapp’s counterfactual arguments." So basically, he passes on addressing the difficult situations. On the other hand, this paper was written in 2009 and some of the newer works were not as well known as today.


2. On the other hand, he says: "Similarly, entangled states of two spin-half ions in a trap, or two photons traveling away from a crystal where they were produced by down conversion, can properly be said to be nonlocal." Yes, this is the situation in which an entangled system has spatial extent. Many authors agree that an entangled systems are not separable and have physical extent in space. And as you say, from that we can make the leap to spatiotemporal extent (distance in space and/or time) and presumably to entanglement between particles with no common past.

So I am quite comfortable with that description of nonlocality in QM, but I point out that going from there to "Quantum Locality" (the paper's title) seems a bridge too far.


3. And this statement was a shocker: "This [definition of classical realism] renders the Bell-CHSH inequality invalid for drawing conclusions about the real (quantum)world, in particular its locality or lack thereof." Hand-waving.

Griffiths has repeatedly maintained a position that he calls "local realism", such as here: "...quantum theory itself is both local and realistic when properly interpreted using a quantum Hilbert space...". That paper is objecting to the famous, well-accepted and well-cited (3367) "loophole-free" experiment of Hensen et al. (2015). Griffiths' objecting paper is cited by 1 author. Science does not rest on number of citations. But I might at least point out his "Consistent Histories" approach (interpretation) was originally developed in 1984, prior to the work I refer to as "modern".

 

[Morbert]

1. First, I criticize him for specifically ignoring GHZ, swapping and other theorems/experiments. "In an article of modest length it is impossible to deal with all published arguments claiming that quantum theory is beset with nonlocal influences and in conflict with special relativity. In particular we do not discuss those based upon the GHZ [60, 61] or Hardy [62] paradoxes, nor Stapp’s counterfactual arguments." So basically, he passes on addressing the difficult situations. On the other hand, this paper was written in 2009 and some of the newer works were not as well known as today.

Modern experiments close loopholes, but consistent histories does not depend on these loopholes. There is nothing unique about GHZ or swapping experiments that pose an additional challenge

3. And this statement was a shocker: "This [definition of classical realism] renders the Bell-CHSH inequality invalid for drawing conclusions about the real (quantum)world, in particular its locality or lack thereof." Hand-waving.

He goes into great non-hand-waving detail in section 5. I will see about starting a new thread specifically on locality and consistent histories.

 

[javisot20]

That’s the whole point of this discussion. Do you consider that in entanglement swapping particles 1 and 4 interacted in any way?

We can say "there is entanglement without interaction in any sense", or deny it, but all the resulting interpretations have to coincide in explaining the same set of experimental data that make up QM, right?

 

[iste]

Do you actually have ant other concrete criticisms to the other thread or paper that was mentioned apart from these?

"Now that I can read it: The Jung paper is horrendously flawed on many levels. I don't even need to refer to the failure to address the Entanglement Swapping experiments.

I should point out that it was published in Frontiers of Physics. That publication is listed as 188th for impact in the area of Physics HERE. Accordingly, I don't believe it should be acceptable for presentation - even in the more lax area of the subforum Foundations/Interpretations. It has a paltry 20 citations since publication in 2020.

Obvious issues:
a. Posits EPR-like mechanisms
b. Builds examples around Polarizer operation (transmission only) when modern experiments use Polarizing Beam Splitters instead.
c. Most importantly: It dismisses Bell's Theorem. "Bell's inequality is misleading because it attributes properties like polarization directions to particles and not to waves. Therefore, Bell cannot take into account phase differences of entangled photons. In future one should ignore violations of Bell's theorem because Bell's considerations are not adequate to describe wave phenomena."

This thread is based on unacceptable non-mainstream science, and should therefore be closed."

How is the journal it is published in and citation count grounds for it to not be acceptable? You're talking about it as if it is some obscure journal that no valid scientists publish in which couldn't be further from the truth. Its a regular peer-reviewed journal. Many papers with high citations have been published there also. I am sure many papers published here are from not big journals or have low citations too. Low citations don't necessarily have to mean anything. There are various reasons a paper may not have become popular in circulation and cited. It doesn't mean it is wrong.

Can you elaborate on what you mean by the criticism a. that it posits EPR-like mechanisms? What exactly do you mean? I am not sure what problem with the mechanism you are alluding to.

Also, what exactly is the significance of criticism b, and why does that impact what they have written? Can you point specifically something in their description that requires one to distinguish different kinds of polarizers of beam-splitters?

c. is also not a real criticism. All that is being said in that paragraph is essentially that Bell violations assume a specific type of local hidden variable or beable with a joint probability distribution. The explanation in the paper avoids that. They aren't saying Bell's theorem is wrong but the mechanism avoids it.

You haven't said one actual substantial criticism of either the paper or what is said in that thread. Your idea that this is based on non-mainstream science is just completely unsubstantiated. There is quite literally nothing in the paper that contradicts anything that has been said in mainstream science. There are no radical out there claims, its claims are about as fair game as any of the other papers or views that are posted here.

So can you actually give any non-handwaving criticisms? Because thats all I see.

I will also point out that I have cited this paper before and you gave a reasonably sized comment to it. (second post of the "Local mechanism for nonlocal anticorrelations inside spin theory" thread). You didn't seem to have a problem with it then as "non-mainstream science" so I wonder what has changed. In that comment you also didn't give any substantial criticisms except for handwaving entanglement swapping.

This seems to be a very consistent pattern of yours where you essentially just respond to any idea with "well entanglement swapping isn't mentioned" even though you never don't give any specific reasons why it can't deal with entanglement swapping (you just seem to assume it can't) and its becoming pretty clear that you throw around this criticism without any actual understanding of the positions you are criticising. I think this was clear in the last Barandes conversation. You just assumed that the Barandes formulation can't handle entanglement swapping without even bothering to even try to understand fully what is being said.

 

[DrChinese]

Modern experiments close loopholes, but consistent histories does not depend on these loopholes. There is nothing unique about GHZ or swapping experiments that pose an additional challenge.

He goes into great non-hand-waving detail in section 5. I will see about starting a new thread specifically on locality and consistent histories.

Sorry, Bell's Theorem is fully accepted in the physics community. There is no amount of hand waving that will justify his position - as of 2015 he rejects both Bell and loophole free Bell tests. By his own words.

And as for the need to consider modern theory and experiment: "Following this somewhat lengthy introduction to the circuit in Fig. 1 let us now use it to search for genuine quantum properties which might be counterparts of, or at least resemble in some way, the mysterious λ that plays a central role in discussions of Bell’s inequality in the literature." In the various entanglement swapping experiments since 2008 I have repeatedly cited (and you have commented on), the final entangled pair are created without having existed in a common light cone. Consequently, there can be no hidden variables λ in the first place. (And why he would ask us to assume there are hidden variables is something of a mystery to me anyway - it's a form of circular reasoning.) So it seems he does condition his reasoning on what you called "coincident pasts of subsystems" which is in fact λ.

Ultimately, it is difficult for me to understand how what he refers to as "properly ... nonlocal" in one spot (a good start) becomes "local and realistic" later (which is clearly a violation of Bell). Which represents his true view?

 

[DrChinese]

Do you actually have any other concrete criticisms to the other thread...

Out of respect for you, but without in any way touching on it further: That thread was closed for a reason. I fully support ending further discussion of that paper.

I have literally a hundred bookmarks of papers denying Bell, asserting Local Realism under a variety of names or guises, and/or asserting physics already disproven by experiment. It is not helpful to pull such references out and discuss each and every one individually as if it is generally accepted science. It's not fair to readers and participants.

 

[iste]

Out of respect for you, but without in any way touching on it further: That thread was closed for a reason. I fully support ending further discussion of that paper.

I have literally a hundred bookmarks of papers denying Bell, asserting Local Realism under a variety of names or guises, and/or asserting physics already disproven by experiment. It is not helpful to pull such references out and discuss each and every one individually as if it is generally accepted science. It's not fair to readers and participants.

But the paper doesn't deny Bell. The paper is about deriving Bell correlations that violate Bell's inequalities. The paper explicitly asserts that what they are saying doesn't imply realism. They are giving a mechanism which is Bell non-local, violates Bell inequalities, has no local hidden variables - all they are saying is that you can violate Bell inequalities with a mechanism that doesn't imply FTL signalling. This is not a denial of Bell or standard quantum mechanics or local realism.

This is yet another example of you just failing to understand what you are reading.

I think it is therefore very relevant to know what other objections you have considering that the paper doesn't say what you say it does.

 

[pines-demon]

We can say "there is entanglement without interaction in any sense", or deny it, but all the resulting interpretations have to coincide in explaining the same set of experimental data that make up QM, right?

Yes the predictions are the same. Generally, in entanglement swapping particles 1 and 4 do not interact locally (being in the same place), however different interpretations consider that particles can interact nonlocally (or not).

 

[pines-demon]

If you can’t flip the order in some reference frame, they cannot be made to look simultaneous either.

Sure, I am not denying that, I just found simultaneity more important for describing the particles as coexisting in response to another user.

It’s a question of distance apart in spacetime. I gave you a specific example. Why don’t you address that one, and show some reference frame where the A and B events are simultaneous?

Again I was not necessarily addressing your comment, but it is a general statement that works for your case if events are spacelike.

Edit: ah you were talking about the $x<1$m-3ns experiment? sure that is no longer spacelike.
Edit2: this remark about spacelike events is important because if the events cannot be made spacelike, at least in principle, means that there could be some loophole where both particles interact in some way.
Edit3: If events are spacelike and action-at-a-distance exists, then it does not matter when the two events happened. If the events are not spacelike, you can posit that some ordinary force imposes the correlations.

 

[javisot20]

I assumed that two particles that act as if entangled without any interaction or influence in any sense don't need to share any type of information to acting like this (is this a reasonable assumption?)

These particles show quantum correlations when all the coincidences and causalities happen for this to happen, without having interacted directly in any sense. Finding two finance agents who, without having ever interacted, show quantum correlations in their way of acting seems complicated, but quantum particles are simpler and more fundamental than finance agents.

 

[pines-demon]

I assumed that two particles that act as if entangled without any interaction or influence in any sense don't need to share any type of information to acting like this (is this a reasonable assumption?)

These particles show quantum correlations when all the coincidences and causalities happen for this to happen, without having interacted directly in any sense. Finding two finance agents who, without having ever interacted, show quantum correlations in their way of acting seems complicated, but quantum particles are simpler and more fundamental than finance agents.

Two particles that never ever have interacted in any way can behave as if entangled, that is no mystery. The mystery is that we can produce many of them and show that the pairs in the ensemble behave as if entangled (even if the pair of particles have never interacted locally). This requires measurements in different angles, and in principle there is no mechanism for the particles to know which angles are going to be measured. We perform as many experiment as to show that this is not just some statistical coincidence.

 

[Morbert]

Sorry, Bell's Theorem is fully accepted in the physics community. There is no amount of hand waving that will justify his position - as of 2015 he rejects both Bell and loophole free Bell tests. By his own words.

He doesn't reject Bell's theorem at all. He (and many others) reject the claim that Bell's theorem necessarily implies Einsteinian nonlocal influence.

And as for the need to consider modern theory and experiment: "Following this somewhat lengthy introduction to the circuit in Fig. 1 let us now use it to search for genuine quantum properties which might be counterparts of, or at least resemble in some way, the mysterious λ that plays a central role in discussions of Bell’s inequality in the literature." In the various entanglement swapping experiments since 2008 I have repeatedly cited (and you have commented on), the final entangled pair are created without having existed in a common light cone. Consequently, there can be no hidden variables λ in the first place. (And why he would ask us to assume there are hidden variables is something of a mystery to me anyway - it's a form of circular reasoning.) So it seems he does condition his reasoning on what you called "coincident pasts of subsystems" which is in fact λ.

Consistent histories rejects hidden variables. The point is without λ, you don't have to infer nonlocal influences.

 

[gentzen]

He doesn't reject Bell's theorem at all. He (and many others) reject the claim that Bell's theorem necessarily implies Einsteinian nonlocal influence.

Consistent histories rejects hidden variables. The point is without λ, you don't have to infer nonlocal influences.

Yes, it doesn‘t reject Bell‘s theorem. However, it cannot go beyond statistical interpretations. So exactly the opposite of what DrChinese wants.

 

[Morbert]

Yes, it doesn‘t reject Bell‘s theorem. However, it cannot go beyond statistical interpretations. So exactly the opposite of what DrChinese wants.

Could you expand on this? For example
https://journals.aps.org/ppf/pdf/10.1103/PhysicsPhysiqueFizika.1.195

In a theory in which parameters are added to quantum mechanics to determine the results of individual measurements, without changing the statistical predictions, there must be a mechanism whereby the setting of one measuring device can influence the reading of another instrument, however remote. Moreover, the signal involved must propagate instantaneously, so that such a theory could not be Lorentz invariant.

Taking this to be Bell's theorem, Consistent Histories does not challenge it. According to Griffiths, Consistent Histories offers a realistic interpretation of QM without the need for parameters that "are added to quantum mechanics to determine the results of individual measurements".
[edit] Sorry I misread "Yes, it doesn‘t reject Bell‘s theorem" as "Yes, it does reject Bell‘s theorem"

 

[Morbert]

Yes, it doesn‘t reject Bell‘s theorem. However, it cannot go beyond statistical interpretations. So exactly the opposite of what DrChinese wants.

Consistent histories doesn't limit us to statistical interpretations if we adopt a Bayesian interpretation of probabilities.