I A new realistic stochastic interpretation of Quantum Mechanics

[DrChinese]

... Particles interact in the past before they are measured, causing a correlation between them which is preserved when the particles are separated and subsequently measured.

... even though the straightforward analysis is that the correlation between the particles can be directly attributed to an initial local interaction between the particles that is subsequently remembered even when they are moved far apart, ...

Droplets interact in the same fluid bath and become correlated so that their dynamics are nonseparable. A barrier is erected which isolates the particles so they can no longer communicate in any way. But despite their isolation, their behavior still maintains correlations between them which can be attributed to the fact that they have been remembered by the now-isolated respective particle-bath systems. This description models quite closely to Barandes' description of entanglement ...

And if you go back to comments I made in the first page of this thread (March 5!), you will see my specific objection to the Barandes' paper. Namely, that he does NOT address modern experiments that rule out his approach. Specifically, experiments such as this from 2008:

High-fidelity entanglement swapping with fully independent sources
Rainer Kaltenbaek, Robert Prevedel, Markus Aspelmeyer,
and Anton Zeilinger (shared a Nobel for this and other works)

Now, I realize this is the Interpretations subforum. If an interpretation contains the same math/predictions as garden variety QM, then it should cover experiments such as this. I don't think it does! But more importantly, your statements above (presumably echoing Barandes at some level) are flat out contradicted by my citation of a well-accepted experiment.

There is NO requirement that that entanglement correlations between 2 particles must follow from an earlier interaction which is "remembered". In the cited experiment, the entangled particles have never existed in a common light cone, and have never interacted in any way. They are created from different sources. Via entanglement swapping, they test "the entanglement of the previously uncorrelated photons 1 and 4".

In the "Experimental Delayed Choice" version (2012), the choice to entangle the 2 particles is freely chosen at a 3rd location - after 1 and 4 are detected. Clearly, nothing is "remembered". This is standard QM theory, and these are factual counterexamples to any variation of an assertion that entanglement requires a past interaction of any kind.

Any interpretation/explanation/belief that contradicts established experiment must be rejected out of hand, of course.

-DrC

 

[Fra]

There is NO requirement that that entanglement correlations between 2 particles must follow from an earlier interaction which is "remembered". In the cited experiment, the entangled particles have never existed in a common light cone, and have never interacted in any way. They are created from different sources. Via entanglement swapping, they test "the entanglement of the previously uncorrelated photons 1 and 4".

In the "Experimental Delayed Choice" version (2012), the choice to entangle the 2 particles is freely chosen at a 3rd location - after 1 and 4 are detected. Clearly, nothing is "remembered".

But there is a requirement is that you have two pairs of prepared correlated particles - each pair might "remember" the relation to it's partner. And then via the clever swapping measuremenent, this allows "transferring" the correlation to 1 and 4, by measuring 2&3 via the swapping setup and use that data to extract the relevant 1 & 4 pairs.

So do not see that Baranders idea per see, is a problem for entanglement swapping? Why would it?

/Fredrik

 

[DrChinese]

But there is a requirement is that you have two pairs of prepared correlated particles - each pair might "remember" the relation to it's partner. And then via the clever swapping measurement, this allows "transferring" the correlation to 1 and 4, by measuring 2&3 via the swapping setup and use that data to extract the relevant 1 & 4 pairs.

So do not see that Baranders idea per see, is a problem for entanglement swapping? Why would it?

/Fredrik

Sorry, but this is again factually incorrect. Yes, there is a swap operation (photons 2 & 3). But it is done far away (in terms of the speed of light) from the measurement of the final entangled pair (1 & 4). And in fact can be done long AFTER their entangled measurements, and be done remotely at the free choice of the experimenter. And the swapping can be chained to further confuse the usual concepts of cause/effect (since order of processes does not matter). In fact, the concept of chained swaps is the basis for long distance quantum networks.

So to recap: there is absolutely NO requirement that entangled particles must have interacted in the past, NOR is there any requirement that some other particles have interacted with them as intermediaries prior to measurement. None of that happens in the Delayed Choice version.


PS There are no 1 & 2 pairs that are entangled/Bell correlated with 3 & 4 pairs initially. This is canonical (look up Monogamy of Entanglement).

 

[PeterDonis]

there is absolutely NO requirement that entangled particles must have interacted in the past, NOR is there any requirement that some other particles have interacted with them as intermediaries prior to measurement. None of that happens in the Delayed Choice version.

I think one caveat is appropriate here, though: the two photons that do interact in the delayed choice experiment (photons 2 & 3) do share an initial preparation with the photons that end up entangled without ever having interacted (photons 1 & 4). AFAIK it is not possible to have two photons (or quantum systems in general) become entangled if they do not meet at least one of four conditions, the first two of which are the ones you mentioned, which are not met in delayed choice experiments:

(1) They have directly interacted with each other;

(2) They have interacted with intermediary systems;

(3) They share a common preparation;

(4) They have shared a common preparation with intermediary systems.

I include (3) just for completeness; it is of course obvious, but is also not met in delayed choice experiments, which is why it has not been mentioned in this or other discussions of them.

Note that (4) is even more indirect than (2): there is no single intermediary system that shares a common preparation with both photons 1 & 4. Rather, there are two separate intermediary systems, photons 2 & 3, each of which shares a common preparation with only one of photons 1 & 4, and then those two intermediary systems interact.

But I don't know of any case where all of the above conditions are not met, but there is still entanglement produced.

 

[PeterDonis]

at least one of four conditions

I think one could formulate a single condition that covers all four cases, by drawing a graph of any experiment involving entanglement as follows:

Draw a node for each event, where "event" means one of these: preparation, interaction, measurement. In the delayed choice experiment under discussion, there would be two preparation nodes, for photons 1&2 and photons 3&4, one interaction node, for photons 2&3 at the BSM, and two measurement nodes, one for photon 1 and one for photon 4.

If a quantum system is involved in both of a pair of events, draw a line from one to the other, marked with that system's identifier. In the delayed choice experiment, there would be a "photon 1" line from "preparation of photons 1&2" to "measurement of photon 1", a "photon 4" line from "preparation of photons 3&4" to "measurement of photon 4", a "photon 2" line from "preparation of photons 1&2" to "interaction of photons 2&3", and a "photon 3" line from "preparation of photons 3&4" to "interaction of photons 2&3".

Then, if one can find a connected subgraph between two measurement nodes, the measurements at those nodes can show entanglement. In this case, the entire graph is itself a connected subgraph from the "measurement of photon 1" node to the "measurement of photon 4" node.

I don't know if this has ever been formulated in this way in the literature.

 

[gentzen]

The pure formalism presented in the two older papers suffered from an unclear status of causal locality. I have not studied the newest paper in any detail yet, but if it manages to overcome this problem, then it constitutes nice incremental progress for this new formulation.

I read some relevant parts of the "new" paper now. I don't think that "it constitutes nice incremental progress for this new formulation". He does his calculation regarding locality in the normal Hilbert space formulation. I admit that he did his definitions regarding locality both in his formulation and in Hilbert space.

Barandes would do better to put his "new formulation" in the context of "quantum reconstructions" rather than "quantum interpretations". (Then he could check whether his math contains new insights, and also whether he was careful enough to show all "expected" continuity properties of his construction with respect to the time parameter t.) And his "Causally Local Formulation" turns out to be just the well known "no signaling" property of QM, verified with calculations done using normal QM (not his new formulation).

 

[gentzen]

From the conclusion of the paper “Is quantum mechanics equivalent to a classical stochastic process?” by H. Grabert, P. Hänggi and P Talkner (Phys. Rev. A 19, 2440 (1979)):

“In this paper we have analyzed the relations between the theory of stochastic processes and the statistical interpretation of quantum mechanics. We have shown that the Schrödinger evolution is not equivalent to a Markovian process, as claimed in several papers. Possible relations to a non-Markovian process have been investigated, and we have shown that the various correlation functions used in quantum theory do not have the properties of the correlations of a classical stochastic process. This leads to the conclusion that quantum mechanics has little if anything to do with the theory of stochastic processes.” [Bold by LJ]

It would be interesting to also hear in your own words how you would argue against Barandes claims. I don't doubt that you are right, in fact I decided to read parts of his new paper because your and A. Neumaier's reaction indicated to me that it is probably "disappointing".

 

[DrChinese]

I think one caveat is appropriate here, though: the two photons that do interact in the delayed choice experiment (photons 2 & 3) do share an initial preparation with the photons that end up entangled without ever having interacted (photons 1 & 4). AFAIK it is not possible to have two photons (or quantum systems in general) become entangled if they do not meet at least one of four conditions, the first two of which are the ones you mentioned, which are not met in delayed choice experiments:

...

(3) They share a common preparation;

(4) They have shared a common preparation with intermediary systems.

Well, I guess I fail to understand how (3) and (4) would appear in an experiment entitled "High-fidelity entanglement swapping with fully independent sources". Emphasis being on the phrase "fully independent", i.e. no common preparation in the normal usage of the language. It is fair to say that the authors of the paper know what "fully independent" means. Specifically, the initial pairs have never interacted.

Perhaps you mean that the common preparation relates to the laser sources? The lasers are synchronized, true, but clearly there exists no known "local causal" physics to explain why pairs coming from different PDC crystals would become entangled at the whim of an experimenter after the entanglement is measured - just because the source lasers have the same phase.

Or perhaps you mean something else. At any rate, the final 1 & 4 pair does not display any correlation unless the swap is executed with 2 & 3 being indistinguishable - this case was specifically tested. So that means there was no entanglement (correlations) present due to the lasers being phase locked.

 

[PeterDonis]

I guess I fail to understand how (3) and (4) would appear in an experiment entitled "High-fidelity entanglement swapping with fully independent sources".

This is the same experiment that I described and that we have been discussing. (3) does not appear in it, as I said in post #334. (4) appears as the common preparation of photons 1&2, and of photons 3&4. Photon 1 and photon 4 of course do not have a common preparation--that's why (3) does not appear. Photons 2 and 3 are the "intermediary systems" in (4).

Post #335 might help to clarify what I mean by (4). The graph I describe in that post is basically Figure 1 of the paper you cite (but without the post-BSM measurements of photons 2 and 3--not that those aren't relevant, just that they aren't needed to have a connected subgraph from the photon 1 measurement to the photon 4 measurement).

 

[iste]

If an interpretation contains the same math/predictions as garden variety QM, then it should cover experiments such as this. I don't think it does!

If Barandes' proof is not faulty then it should cover experiments like that because what it seeks to do is show that any unitarily evolving quantum system can be translated into an indivisible stochastic one and vice versa. Ofcourse, Barandes may be wrong. And Barandes' theory is completely open and agnostic about what can cause indivisibility or how weird those causes could be.

But addressing why you think Barandes' theory cannot account for entanglement swapping: i.e.

There is NO requirement that that entanglement correlations between 2 particles must follow from an earlier interaction which is "remembered". In the cited experiment, the entangled particles have never existed in a common light cone, and have never interacted in any way. They are created from different sources.

,

i don't think entanglement swapping is anything above ordinary entanglement. The additional swapping aspect is just due to transitivity of correlations unveiled by statistical conditioning, quantum mechanics not especially required. In Barandes' papers, collapse is not a physical event, nothing more than statistical conditioning.

In the "Experimental Delayed Choice" version (2012), the choice to entangle the 2 particles is freely chosen at a 3rd location - after 1 and 4 are detected. Clearly, nothing is "remembered". This is standard QM theory, and these are factual counterexamples to any variation of an assertion that entanglement requires a past interaction of any kind

This is not an issue in Barandes' theory where collapse isn't physically real and measurement results do not communicate.

 

[JC_Silver]

I made an account just to answer here because I feel I have one point to add.

Most of Barandes' newer interviews he has done he doesn't touch on the "interpretation" aspect of his paper instead choosing to focus on the "wavefunction is not a real thing" side and I believe this is because he has possibly realized what some here have too, this is not an interpretation of QM, this is a reformulation of the math instead.

And I think that if what Barandes claims is true (I don't have enough knowledge in non-markovian processes to say if his math is correct), I believe it's worth looking into.

Assuming ALL of Quantum Mechanics is a special case of non-Markovian processes, it could be worthy to look into it to see if we can find fenomena where QM can't seem to find an answer (eg. Gravity) to see if the answer lies outside the Markovian assumptions.

I wouldn't call this an interpretation though, much less say it confirms that Pilot Waves are real.

I say the value of this paper is to argue from a new perspective that wavefunction is a math tool to predict the world and that they are not the real object.

 

[pines-demon]

I made an account just to answer here because I feel I have one point to add.

Most of Barandes' newer interviews he has done he doesn't touch on the "interpretation" aspect of his paper instead choosing to focus on the "wavefunction is not a real thing" side and I believe this is because he has possibly realized what some here have too, this is not an interpretation of QM, this is a reformulation of the math instead.

And I think that if what Barandes claims is true (I don't have enough knowledge in non-markovian processes to say if his math is correct), I believe it's worth looking into.

Assuming ALL of Quantum Mechanics is a special case of non-Markovian processes, it could be worthy to look into it to see if we can find fenomena where QM can't seem to find an answer (eg. Gravity) to see if the answer lies outside the Markovian assumptions.

I wouldn't call this an interpretation though, much less say it confirms that Pilot Waves are real.

I say the value of this paper is to argue from a new perspective that wavefunction is a math tool to predict the world and that they are not the real object.

That seems to be the growing consensus here, if the math is right. In that case, Barandes just found a useful duality between quantum and non-Markovian akin to the Osborn's rule or Wick rotations. If it works as an interpretation some of us are still "agnostic".

Of course some have considered that the mathematics might not be right or well funded either. For example Barandes would have to explain how to avoid the result of paper in post #327.

 

[jbergman]

That seems to be the growing consensus here, if the math is right. In that case, Barandes just found a useful duality between quantum and non-Markovian akin to the Osborn's rule or Wick rotations. If it works as an interpretation some of us are still "agnostic".

Of course some have considered that the mathematics might not be right or well funded either. For example Barandes would have to explain how to avoid the result of paper in post #327.

Right. I need to dive deeper l, but right now I think it's a bit of an Emperor's New Clothes situation in that it doesn't say much about Interpretations. It really comes down to understanding this indivisibility condition on the evolution of the transition matrix, but as far as I can tell that doesn't imply things like local realism.

 

[DrChinese]

1. If Barandes' proof is not faulty then it should cover experiments like that because what it seeks to do is show that any unitarily evolving quantum system can be translated into an indivisible stochastic one and vice versa. Of course, Barandes may be wrong. And Barandes' theory is completely open and agnostic about what can cause indivisibility or how weird those causes could be.

2. i don't think entanglement swapping is anything above ordinary entanglement. The additional swapping aspect is just due to transitivity of correlations unveiled by statistical conditioning, quantum mechanics not especially required. In Barandes' papers, collapse is not a physical event, nothing more than statistical conditioning.

3. This is not an issue in Barandes' theory where collapse isn't physically real and measurement results do not communicate.

1. Again, there is no initial "unitarily evolving quantum system" evolving into a "indivisible stochastic one". It begins as *two* widely separated ones, and does not become an "indivisible" one unless and until a remote irreversible interaction at the BSM creates a swap. This is the experiment, and saying his "proof not is faulty" does not make it cover this experiment as it might otherwise for basic PDC entanglement (without a swap).

You are the one who says: Entanglement is always "directly attributed to an initial local interaction". Either Barandes claims this, or he doesn't. Either way, it is factually incorrect (experimentally falsified).


2. This too is factually incorrect: There is no statistical conditioning. ALL cases in which photons 2 & 3 arrive within the specified narrow time window (indistinguishably) lead to a swap, and are counted - and they show perfect correlations (1). All cases in which photons 2 & 3 arrive at the BSM but are made distinguishable fail to lead to a swap, and are counted. They show only random correlations. The only difference is whether the experimenter chooses to make them distinguishable or not.

Normally: when we see the experimenter is able to change the outcomes at will, we conclude that she has control over a causal variable. That variable is a deliberate action, and again normally we would conclude that there must have been a physical interaction between the 2 & 3 at the BSM. After all, the method they use to fail the swap is to delay either 2 or 3 so both 2 & 3 cannot be in the BSM apparatus at the same time (making them distinguishable).

In normal science, this would be considered a proof there was an interaction, and that it is physical. So rejecting this conclusion without any reasonable basis ("Barandes' interpretation is equivalent to other interpretations") is the very example of hand-waving.


3. My point being: how can the interaction at the BSM *not* be physically real, given the facts per 2.?

 

[JC_Silver]

This might be obvious but I honestly don't know the answer. How does Barandes' (and any other pilot wave interpretation) explain quantum tunneling? There shouldn't be any classical fenomena that allows for it, right?

 

[DrChinese]

Photons 2 and 3 are the "intermediary systems" in (4).

OK, that's what I thought you were aiming at. But... how could that work? Actually, I agree that photons 2 & 3 (when indistinguishable at the BSM) do connect initially separate systems 1&2 and 3&4.

But there is no spacetime region in which (in some versions of the experiment) that connection could possibly influence the previous 1 & 4 measurements - everything is distant in terms of c. We are left with 2 causal problems: a) nonlocality is evident (because the relevant measurements occur in widely separated regions); b) Einsteinian causal order is defied (because the outcomes are not dependent on measurement order).

So it seems that any assumption we make regarding how the mechanism works FAILS if we accept the clear experimental evidence for a) and b) I have provided. Keep in mind, I have no idea how nature performs its tricks. But I know that a) and b) must be true, if you accept the experiment as valid.

 

[PeterDonis]

how could that work?

I'm not trying to say anything about how it might work. I'm only trying to describe the conditions that appear to me to be necessary to have entanglement, without making any hypotheses at all about why those are the necessary conditions. I understand that nobody has a mechanism that could explain why. But that doesn't change the fact that, for example, if we take away the "interaction" node at the BSM (in my graph description), entanglement is no longer present--and as you have said, whether or not there is an "interaction" node at the BSM is under the experimenter's control. Nobody understands how it could be that the experimenter can control whether photons 1 & 4 are entangled by choosing whether or not to let photons 2 & 3 interact at the BSM. But that is, factually, the case, as the experiments show. I'm just trying to describe that factual condition in a way that might help to make it clearer exactly what is required.

 

[pines-demon]

This might be obvious but I honestly don't know the answer. How does Barandes' (and any other pilot wave interpretation) explain quantum tunneling? There shouldn't be any classical fenomena that allows for it, right?

The particle does not need to have enough energy to jump over the barrier because it is not following classical physics, it is just guided by the guiding wave function which can tunnel.

 

[JC_Silver]

I thought Barandes was trying to do away with the wavefunction but I guess I need to study more before understanding it

 

[pines-demon]

I thought Barandes was trying to do away with the wavefunction but I guess I need to study more before understanding it

Whatever Barandes is doing would lead to the particle effectively tunneling and thus not following classical physics either.

 

[JC_Silver]

Whatever Barandes is doing would lead to the particle effectively tunneling and thus not following classical physics either.

I see, thanks!

 

[Fra]

OK, that's what I thought you were aiming at. But... how could that work? Actually, I agree that photons 2 & 3 (when indistinguishable at the BSM) do connect initially separate systems 1&2 and 3&4.

But there is no spacetime region in which (in some versions of the experiment) that connection could possibly influence the previous 1 & 4 measurements - everything is distant in terms of c.

This is no answer, but what is wrong with this conceptual outline that ias how I understand it?

1&2 share a "hidden variable"
3&4 share another "hidden variable"

noone else can get they without breaking the entanglement, ie only 1 and 2 themselves, "know" the keys. That is the premise. same with 3 & 4.

If we can escape bells inequality, it could explain bother experiments and correlations. By "matching" the keys of 2&3; we know 1&4 keys correlate as well but without know what they are. - no spacetime region needed.

But the tentative escape of bells ansatz is that it is not possible to make a markov division of the process indexed by these hidden keys; because the interaction itself is influenced by the fact that the keys are hidden. So bell theorem does not apply to such KIND of hidden variable.

Baranade has no such theory but argues for its possibility? That one has trouble to even imagine what such as theory would be like, is a separate problem.

/Fredrik

 

[iste]

I made an account just to answer here because I feel I have one point to add.

Most of Barandes' newer interviews he has done he doesn't touch on the "interpretation" aspect of his paper instead choosing to focus on the "wavefunction is not a real thing" side and I believe this is because he has possibly realized what some here have too, this is not an interpretation of QM, this is a reformulation of the math instead.

And I think that if what Barandes claims is true (I don't have enough knowledge in non-markovian processes to say if his math is correct), I believe it's worth looking into.

Assuming ALL of Quantum Mechanics is a special case of non-Markovian processes, it could be worthy to look into it to see if we can find fenomena where QM can't seem to find an answer (eg. Gravity) to see if the answer lies outside the Markovian assumptions.

I wouldn't call this an interpretation though, much less say it confirms that Pilot Waves are real.

I say the value of this paper is to argue from a new perspective that wavefunction is a math tool to predict the world and that they are not the real object.

There are definitely parts of his latest interview where he implies this has fully interpretational consequences, parts where he talks about no need for observers I remember distinctly, as well as other parts. Its very general but it is unambiguous that the theory, if true, implies particles are always in one configuration at a time. That 100% implies some kind of interpretation that is different to what the great majority of people currently think, and would completely deflate things like the measurement problem. There is no way he could talk about this deflating quantum mechanics or making it more boring if there wasn't some tangible interpretational element here, even if not everything is explained about why quantum mechanics would be that way. The wavefunction not being real is in and of itself part of interpretation. True, what he would be pushing here is a distinct formulation of quantum mechanics, but it directly implies an interpretation too - the kind it shares with stochastic mechanics.

That seems to be the growing consensus here, if the math is right. In that case, Barandes just found a useful duality between quantum and non-Markovian akin to the Osborn's rule or Wick rotations. If it works as an interpretation some of us are still "agnostic".

Of course some have considered that the mathematics might not be right or well funded either. For example Barandes would have to explain how to avoid the result of paper in post #327

If it was just like Wick rotation, Barandes wouldn't be going on about how the wave function isn't real or quantum mechanics becomes more boring or observers are deflated.

And if you look at the bottom of that paper at the conditions required to satisfy classical stochastic processes in terms of a two-time correlation function - I am pretty sure that at the core of Barandes' idea is that this kind of thing is violated. The classical two-time correlation function implies divisibility. So Barandes doesn't have to avoid the result because the indivisible stochastic process is not of the kind of stochastic process the paper is using to compare to quantum mechanics and saying is incompatible. The Barandes process is compatible.

This might be obvious but I honestly don't know the answer. How does Barandes' (and any other pilot wave interpretation) explain quantum tunneling? There shouldn't be any classical fenomena that allows for it, right?

The particle does not need to have enough energy to jump over the barrier because it is not following classical physics, it is just guided by the guiding wave function which can tunnel.

I don't know anything about this topic but I have seen it mentioned in the context of stochastic mechanics, e.g. this paper:

https://scholar.google.co.uk/schola...2266132&hl=en&as_sdt=0,5&as_yhi=1990&as_vis=1
https://www.mdpi.com/2218-1997/7/6/166

I quote from first paper but says similar in second recent paper:

"The energy in stochastic mechanics is a randomly fluctuating
quantity which is always non-negative just as in Newtoni-
an mechanics. Thus a stochastic mechanical system never actually "tunnels" through a potential barrier; rather, it is "kicked" over the barrier by a large enough positive energy fluctuation resulting from a configuration fluctuation."

Presumably, similar would be the case if it could be formulated in Barandes' theory. Or maybe not. It seems reasonable to me that the Barandes model would do the same thing if it could be formulated. But there is no evidence for that other than stochastic mechanics and Barandes' model fall broadly under the same interpretational hat and they both claim to derive or prove some correspondence between quantum mechanics and stochastic systems.

 

[DrChinese]

I'm not trying to say anything about how it might work. I'm only trying to describe the conditions that appear to me to be necessary to have entanglement, without making any hypotheses at all about why those are the necessary conditions. I understand that nobody has a mechanism that could explain why. But that doesn't change the fact that, for example, if we take away the "interaction" node at the BSM (in my graph description), entanglement is no longer present--and as you have said, whether or not there is an "interaction" node at the BSM is under the experimenter's control. Nobody understands how it could be that the experimenter can control whether photons 1 & 4 are entangled by choosing whether or not to let photons 2 & 3 interact at the BSM. But that is, factually, the case, as the experiments show. I'm just trying to describe that factual condition in a way that might help to make it clearer exactly what is required.

My bad, I wasn't trying to actually ask about the underlying mechanism for entanglement swapping - but I see why it looks that way.

What I meant was: Yes, there is one of your nodes at the BSM when swapping is active. No disagreement there. And you punted on the question of whether it was an "interaction" or a (joint) measurement. But for anyone wanting to draw Einsteinian causality/locality into the equation (by assumption of course), how would that serve as an "out"? It won't. If there is no opportunity for an interaction at the 2&3 beam splitter, there is no swap. That is true regardless of where or when the BSM is located/executed.

As I re-read your post, I don't think there is a disagreement. It is a true statement that as far as I know, there must be something like the nodes you describe to enable entanglement. However, they don't need to respect locality and/or causality between the end nodes.

Ken Wharton refers to your diagram as a "W" entanglement type, for the entanglement swapping setups. For the more common entanglement from a single PDC crystal, he calls that a "V".

 

[DrChinese]

This is no answer, but what is wrong with this conceptual outline that ias how I understand it?

1&2 share a "hidden variable"
3&4 share another "hidden variable"

noone else can get they without breaking the entanglement, ie only 1 and 2 themselves, "know" the keys. That is the premise. same with 3 & 4.

If we can escape bells inequality, it could explain bother experiments and correlations. By "matching" the keys of 2&3; we know 1&4 keys correlate as well but without know what they are. - no spacetime region needed.

But the tentative escape of bells ansatz is that it is not possible to make a markov division of the process indexed by these hidden keys; because the interaction itself is influenced by the fact that the keys are hidden. So bell theorem does not apply to such KIND of hidden variable.

Baranade has no such theory but argues for its possibility? That one has trouble to even imagine what such as theory would be like, is a separate problem.

/Fredrik

OK, this is the point I keep making - and apparently I am not explaining well enough.

So there are 2 initial "keys" (1&2 and 3&4) according to your hypothetical explanation. You think that if you know ("match") those keys, you can predict the 1&4 entanglement. There are a lot of reasons* what that cannot be true. But I will focus on the one related to the BSM and whether swapping is enabled or not.

When entanglement is enabled: we read those keys - and make a prediction that is certain (correlation=1). When entanglement is not enabled: we read the exact same keys! But the outcome is random (correlation=0). This is actually performed in the Ma paper ("Experimental delayed-choice entanglement swapping"). Obviously, there are no keys/hidden variables as you want to describe them.

To repeat: everything registers the same at the BSM regardless of whether there is a swap or not. But there is only a swap if the 2 and 3 photons overlap within a narrow time window - so they are allowed to interact (and they must be indistinguishable). The experimenters delay the "2" (or "3") photon if they don't want a swap to occur. But you assert the photons already possessed whatever property value is being measured regardless of timing. And you assert there is no physical interaction capable of affecting the 1&4 photons in any way due to their overlapping in the beam splitter.

So whether they overlap or not shouldn't even matter from your perspective. But experiment says otherwise. And the results are pretty much back or white.


*Violation of a Bell Inequality in swapping experiments also disproves the "key" idea, which is just another attempt at a local hidden variable model with a different label.

 

[iste]

This is the experiment, and saying his "proof not is faulty" does not make it cover this experiment as it might otherwise for basic PDC entanglement (without a swap).

If entanglement swapping is a process of a unitarily evolving quantum system then I don't understand why what you say would be the case  if Barandes was correct. He would claim that he has proved that he could convert that description into a stochastic system.

irreversible interaction at the BSM creates a swap

Collapse may not be real. It is not a foregone conclusion that it is and several functioning formulations of quantum mechanics do not have a physical collapse. On a formal level, Barandes explicitly identifies the collapse as simply statistical conditioning with no physical content.

You are the one who says: Entanglement is always "directly attributed to an initial local interaction". Either Barandes claims this, or he doesn't. Either way, it is factually incorrect (experimentally falsified).

My thoughts is that the entanglement part of entanglement swapping is quantum; we then have two different entangling scenarios going on, both respectively caused by initial local interactions.

The swapping part, even though clearly is occuring in quantum systems is not really quantum at all. You can make sense of this with any kind of set of correlations that: if A and B are correlated, and then C and D are correlated, then if you correlate B and C, A and D will be correlated. This kind of reasoning can be applied to literally anything.

You can correlate B and C by simply conditioning on two of their respective outcomes. If you do not condition on two of their respective outcomes, there will clearly be no correlation if all the outcomes occur because clearly all of the pairs - B1C1, B1C2, B2C1, B2C2 - can occur equally. If outcomes from A and D have a one-to-one mapping with those of B and C, then there will clearly be no correlation between A and D either because there is none between B and C. But if you condition on B1C1, you are going to get the same pair of outcomes for A and D all the time so they are now correlated.

You don't need quantum mechanics to justify these correlations beyond the regular entanglements.

2. This too is factually incorrect: There is no statistical conditioning. ALL cases in which photons 2 & 3 arrive within the specified narrow time window (indistinguishably) lead to a swap, and are counted - and they show perfect correlations (1). All cases in which photons 2 & 3 arrive at the BSM but are made distinguishable fail to lead to a swap, and are counted. They show only random correlations. The only difference is whether the experimenter chooses to make them distinguishable or not

A Bell state measurement is equivalent to statistical conditioning in the Barandes framework. It is an experimental exercise in statistical conditioning.

My thoughts are that indistinguishability is a requisite for the coherence required for the Bell state. In Barandes' formulation, an intrusive interaction with an entangled state would cause it to lose its correlation and coherencr, due to something called a division event. Presumably, distinguishability for the Bell state is like that, like the way a measurement causes decoherence or which-way information ruins interference. Those are all covered by division events which would ruin the kind of entangled states, the kind of correlations that allow the conditioning exercise I have just given.

3. My point being: how can the interaction at the BSM *not* be physically real

Only physical collapse isn't real, but if you allow (i.e. construct the experimental conditions conducive to allow) the two different entangled systems to correlate and pretend there is a collapse (i.e. just statistical conditioning maybe without even knowing it), you will get the correlations naturally just by assuming regular conventional entanglement.

 

[PeterDonis]

here is one of your nodes at the BSM when swapping is active. No disagreement there.

Ok, good.

And you punted on the question of whether it was an "interaction" or a (joint) measurement.

For my formulation it doesn't matter which it is. All three kinds of nodes serve the same function as far as determining whether there is a connected subgraph.

for anyone wanting to draw Einsteinian causality/locality into the equation (by assumption of course), how would that serve as an "out"? It won't.

I wasn't trying to address such questions; to me they are part of the "how" that I wasn't discussing. I don't think my formulation gives any particular help to any particular attempt at interpretation of the "how". It's just a way of describing exactly what conditions are required for entanglement according to the experimental facts.

However, they don't need to respect locality and/or causality between the end nodes.

Yes, of course.

Ken Wharton refers to your diagram as a "W" entanglement type, for the entanglement swapping setups. For the more common entanglement from a single PDC crystal, he calls that a "V".

Ah, ok. I figured someone had come up with something similar already.

 

[Fra]

OK, this is the point I keep making - and apparently I am not explaining well enough.

So there are 2 initial "keys" (1&2 and 3&4) according to your hypothetical explanation.

Or i was thinking in terms of 2 pairs or correlates keys. The bsm serves to find the new 2&3 pairs that "match" then we know corresponding 1&4 do.

You think that if you know ("match") those keys, you can predict the 1&4 entanglement. There are a lot of reasons* what that cannot be true. But I will focus on the one related to the BSM and whether swapping is enabled or not.

When entanglement is enabled: we read those keys - and make a prediction that is certain (correlation=1). When entanglement is not enabled: we read the exact same keys! But the outcome is random (correlation=0). This is actually performed in the Ma paper ("Experimental delayed-choice entanglement swapping"). Obviously, there are no keys/hidden variables as you want to describe them.

I dont follow your issue as i see no problem here.

i am getting convinced that you think the HV necessarily defines the states, as they do in bells thinking. This the difference between ignorance HV and HV that are "subjective" ie subjective to 1&2 and 3&4 only. They are exposed only upon physicaö interaction

But you assert the photons already possessed whatever property value is being measured regardless of timing.

No, i didnt say that. I said the photons are correlated; they are not determined one by one.

And you assert there is no physical interaction capable of affecting the 1&4 photons in any way due to their overlapping in the beam splitter.

The 2&3 interaction is physical and required to identify the 1&4 that are correlated. info from bsm are classically transmitted.

So whether they overlap or not shouldn't even matter from your perspective.

Of course it matters. The DATA from bsm is the key of the protocol. you probably assume the photon states are predtermined relative to environmebt from HV. That is not what i suggest.

*Violation of a Bell Inequality in swapping experiments also disproves the "key" idea, which is just another attempt at a local hidden variable model with a different label.

No, what i lined out is not a bell style HV theory.

Hidden key pair does NOT predetermine the photons, the only define their relation. This keys have no relation to the environment. This is how they are hidden. So not same as "ignorance". Which is imo related to the lack of markov indivisibility.

/Fredrik

 

[pines-demon]

There are definitely parts of his latest interview where he implies this has fully interpretational consequences, parts where he talks about no need for observers I remember distinctly, as well as other parts. Its very general but it is unambiguous that the theory, if true, implies particles are always in one configuration at a time. That 100% implies some kind of interpretation that is different to what the great majority of people currently think, and would completely deflate things like the measurement problem. There is no way he could talk about this deflating quantum mechanics or making it more boring if there wasn't some tangible interpretational element here, even if not everything is explained about why quantum mechanics would be that way. The wavefunction not being real is in and of itself part of interpretation. True, what he would be pushing here is a distinct formulation of quantum mechanics, but it directly implies an interpretation too - the kind it shares with stochastic mechanics.

You said before that one could be agnostic given the state of the theory. Now you are eager to defend there is some interpretation. I do not think it is worth it unless he provides more content about it. I mean Barandes wants to provide us right away with interpretational conclusions but gives no intuitive mechanism on how to understand an indivisible stochastic process. That's what we need to understand here, because even if equivalent to quantum mechanics it is equally mysterious and nonclassical. He is proposing some stocastic force that permeates space and allows to bypass Bell's theorem. In most cases that would mean that his theory is nonlocal.

Bohmian mechanics also has one configuration at a time, superdeterminism does to.

If it was just like Wick rotation, Barandes wouldn't be going on about how the wave function isn't real or quantum mechanics becomes more boring or observers are deflated.

Well it can be both a mathematical duality and an interpretation. However for me it is not deflational in the sense that we have other similar interpretations and Barandes interpretation barely provides a way to think about it. Also the duality seems to be between quantum mechanics and indivisible non-Markovian processes (INMP). The latter is not well studied at all, so quantum mechanics (QM) can help INMP more than INMP can help QM.

And if you look at the bottom of that paper at the conditions required to satisfy classical stochastic processes in terms of a two-time correlation function - I am pretty sure that at the core of Barandes' idea is that this kind of thing is violated. The classical two-time correlation function implies divisibility. So Barandes doesn't have to avoid the result because the indivisible stochastic process is not of the kind of stochastic process the paper is using to compare to quantum mechanics and saying is incompatible. The Barandes process is compatible.

People have tried to break the axioms of probability before to get quantum mechanics without amplitudes but that does not mean it is easier to comprehend or to interpret. Is Barandes proposal even a stochastic process at this point? We really need a simple example, hopefully a classical one.

 

[Fra]

3. My point being: how can the interaction at the BSM *not* be physically real, given the facts per 2.?

For me the BSM is certainly real, but i do not see it as a measurement of keys of 2 & 3 it measure of the relation. Knowing the relation between 2 keys, is the output in my conceptual world.

/Fredrik