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But the math is unanimously telling the statistical properties for the outcome of measurements, independent of any metaphysical believes.
Yes, that's correct. It also doesn't contradict anything I said.vanhees71 said:the math is unanimously telling the statistical properties for the outcome of measurements
What do you mean by an individual run? Is that 1 photon from each source being considered in the experiment as a run? Or does that mean many photons from each source with a fixed measurement considered in the experiment as a run?PeterDonis said:But @DrChinese is using a different interpretation, in which the quantum state describes each individual run, not an ensemble of runs. What you call "subensembles" to him are just particular sets of runs described by particular conditions. The fact that the full set of runs does not show the same correlations as the particular set he is interested in is irrelevant on the interpretation he is using.
Each individual set of photons 1 through 4, prepared and going through the experiment as described in the experimental protocol.kurt101 said:What do you mean by an individual run?
I only wanted to argue against your statement that all this depends on "interpretation", as if there'd be no objective scientific meaning of QT. That's the greatest harm done by the early overemphasis of philosophy by part of the "founding fathers" of QT.PeterDonis said:Yes, that's correct. It also doesn't contradict anything I said.
I said no such thing. I was quite specific about what is interpretation and what isn't.vanhees71 said:I only wanted to argue against your statement that all this depends on "interpretation"
Correct. We have never had a disagreement on these points.vanhees71 said:It's clear that you can't in any way choose which Bell state occurs at will and thus you can't send a message in this way. That's interpretation independent.
Careful. Statements like this...DrChinese said:This is an objective result, not subject to interpretation.
DrChinese said:causing the distant 1,4 to become anti correlated - or be completely uncorrelated
...are interpretation dependent. They are not "objective results". We can observe statistics, but we can't directly observe causation. And "strict EInsteinian causality", in QFT terms, becomes what @vanhees71 calls "microcausality"--spacelike separated measurements must commute. Which is not violated in these experiments (indeed, the results commute regardless of the spacetime relationship between the measurement events).DrChinese said:strict Einsteinian causality is not preserved
Please see my post #58, where I analyze the psi- case specifically.mattt said:@DrChinese
If the swap fail for some of the runs (deliberate or not) then you can partition the whole ensemble in five subensembles (the four ones like in the ideal case, plus another subset that corresponds to the failed swap runs).
And still the whole ensemble (the union of the five subsets) of the (1,4) pairs is characterized by the same statistics (state) as in the beginning.
You may think that "something changed" for each individual (1,4) pair (depending on the deliberate action of the experimenter at (2,3) site to fail or not fail the swap) only if you think that the state is a physical property of each (1,4) pair.
It adds nothing essentially new in this respect to the EPR type experiments.
The measured statistics change, according to the experimenter’s choice. I’d call that objective. Correlated/anti correlated vs no correlation at all.PeterDonis said:Careful. Statements like this...
...are interpretation dependent. They are not "objective results". We can observe statistics, but we can't directly observe causation.
That's not the claim I quoted as being interpretation dependent.DrChinese said:The measured statistics change, according to the experimenter’s choice. I’d call that objective.
I am suspicious of this claim. It sounds like you are carrying out an intermediate measurement which would affect the [2,3] pair, such that if you register a psi- or psi+ you can no longer be sure you would have registered that same result even if you hadn't added the delay. Can you provide the explicit time-evolution of the two scenarios (delay vs no delay)? Or some expression a la equation 3 in this paper that distinguishes the the two cases?DrChinese said:You get this same information (identifying psi- or psi+) whether the experimenter flips the photon 2 delay switch (which fails the swap) or not.
Fair question.Morbert said:I am suspicious of this claim. It sounds like you are carrying out an intermediate measurement which would affect the [2,3] pair, such that if you register a psi- or psi+ you can no longer be sure you would have registered that same result even if you hadn't added the delay. Can you provide the explicit time-evolution of the two scenarios (delay vs no delay)? Or some expression a la equation 3 in this paper that distinguishes the the two cases?
Indeed, this is why I thought it would be the best example to better understand your claim.DrChinese said:Interestingly, this experiment actually demonstrates exactly what I am saying.
From the paperDrChinese said:Fair question.
Sure, I am familiar with your reference. Equation 3 presents all four Bell states. We will focus on a single of those four, the phi- Bell state, which they seek. The BSM uses a projecting PBS instead of a beam splitter for the first test, but the principle is the same as other setups. The second test consists of a polarizing beam splitter at each of the output ports of the projecting PBS. There are then photon detectors at each of those output ports, four in total.
The desired phi- state requires the 2,3 photons to exit different output ports of the projecting PBS. They must end up as hv or vh in the final polarization test. In this case, the 1,4 photons become cast into a perfectly anti-correlated state. Analogously, when the phi+ State occurs, the 1,4 photons become cast into a perfectly correlated state.
Interestingly, this experiment actually demonstrates exactly what I am saying. Not sure why I missed this on previous reading, but here it is in black and white. See figure 3c and related text (the paragraph beginning with “One can also choose…”). They used Temporal delay to create the distinguishability. The results are exactly as I predicted. Which is, of course, in keeping with usual quantum mechanics.
Once again: the experimenter may choose to have a successful swap, or not, while retaining all the information needed to discriminate between Bell states which occur randomly. When the experimenter adds delay to cause the swap to fail due to distinguishability, the remote 1,4 photons objectively change their state (as demonstrated from the density matrices of figure 3) from entangled to unentangled.
I read this to mean, when distinguishability is established, the apparatus can no longer project onto |φ+〉 or |φ−〉 and instead projects onto some state ##a|\phi^+\rangle\langle\phi^+| + b|\phi^-\rangle\langle\phi^-|##. How do you square this with your claimIn this case [distinguishability], the phase between the two terms of the |φ〉 projected state is undefined, resulting in a mixture of |φ+〉 and |φ−〉 in the projected state, and the first and last photons do not become quantum entangled but classically correlated.
because it sounds like you lose the ability to identify phi+ or phi- and must settle for a mixture. The caption under figure 3c calls this case a failure to project.You get this same information (identifying psi- or psi+) whether the experimenter flips the photon 2 delay switch (which fails the swap) or not.
Fine, so where's finally the disagreement? Let's see...DrChinese said:Correct. We have never had a disagreement on these points.
Yes, that's the most simple case, because here you can deal with a simple beam splitter. The disadvantage is that you can only filter out one of the four interesting projections, i.e., only to the "singlet Bell state". So a complete Bell-state analysis is favorible, because then you can a posteriori (delayed choice!) look at the four interesting sub-ensembles. But anyway, for the discussion of the locality/causality issue it's enough.DrChinese said:Let’s focus on a single Bell state, psi-. This state occurs 25% of the time, and is of course random. The identifying characteristics are the 2,3 photons emerging from separate Beam Splitter ports, and polarizations orthogonal.
If the 2,3 photons are projected to ##\psi^-##, they are indeed indistinguishable. That's the whole point of this state being a maximally entangled state, i.e., a "Bell state". Of course, for this perpose the experimenter doing the projection must project to this Bell state. This experiment then doesn't tell you anything about what would have been found when doing another experiment, i.e., QT does not tell anything about experiments that haven't been performed or measurements that cannot be performed given the measurement really done. E.g., in an SG experiment you can measure the spin component in one direction but not at the same time in another direction, because the direction is uniquely chosen only with a correspondingly directed and taylored magnetic field. The same holds here for polarization measurements. You have to choose which observations you want to make, i.e., measuring the polarization of single photons in a specific direction, which then of course never leads to the projection to an entangled state or you can decide to project to a Bell state.DrChinese said:Our experimenter at the BSM sees those random cases that identify as psi-. That means 2,3 are triggering 2 detectors that identify them per above. When those specific combinations are registered, the related 1,4 pairs will be perfectly anti-correlated at all angles… but only if the 2,3 photons are indistinguishable! So when the 1,4 pairs that have been identified as psi- are reviewed, there will be no statistical relationship when the experimenter flips the switch one way, and will be a perfect match to the quantum expectation when the switch is flipped the other way.
I think, we agree up to this point.DrChinese said:The experimenter makes a choice, flipping a switch, causing the distant 1,4 to become anti correlated - or be completely uncorrelated. Depending on whether there is indistinguishability…
Now, you are contradicting yourself again. If there is no FTL signalling possible, then relativistic causality is preserved, i.e., in other words, there are no causal connections between space-like separated events possible, then relativistic causality is fulfilled. Maybe you have another definition for what you call "Einsteinian causality". Maybe what you in fact mean is not causality but determinism or, in the sense of the original paper of Bell's (obviously he changed his terminology over time, as I learnt recently from some paper, mentioned in one of the threads her on PF, which I can look for again if needed) "realism", i.e., the believe that all observables of a system must always take determined values, independent of the state of the system. This contradicts standard QT and that's why "hidden variables" are invoked, that are unknown and unobservable, so that the probabilities come in only due to "ignorance" (which may not be avoidable from first principle, if for some reason the hidden variables are not even in principle determinable in any way), i.e., as in classical statistical physics.DrChinese said:This is an objective result, not subject to interpretation. I say it rules out an entire class of interpretations. There is no FTL signaling, but strict Einsteinian causality is not preserved. The order of measurements is not a factor, and light cones are not a limiting factor.
DrChinese said:Please see my post #58, where I analyze the psi- case specifically.
When the experimenter fails the swap, he still gets the same information about the Bell state that would have been been obtained had the swap succeeded. There’s no difference in which detectors are triggered. The only change is distinguishability, which fails the swap but still allows the Bell state to be identified (if the swap had succeeded).
Sure, the same detectors are present, and so that data becomes available just as when a swap occurs. It shows which Bell state would’ve been identified, if the swap had actually occurred. Of course, no swap… no true Bell state. From the paper:Morbert said:Indeed, this is why I thought it would be the best example to better understand your claim.From the paper I read this to mean, when distinguishability is established, the apparatus can no longer project onto |φ+〉 or |φ−〉 and instead projects onto some state ##a|\phi^+\rangle\langle\phi^+| + b|\phi^-\rangle\langle\phi^-|##. How do you square this with your claim because it sounds like you lose the ability to identify phi+ or phi- and must settle for a mixture. The caption under figure 3c calls this case a failure to project.
I think you have cleared something up for me. You use the words “locality” and “non-locality” differently than most authors, including the most recent reference from Eisenberg et al: “The observed quantum correlations manifest the non-locality of quantum mechanics in spacetime.” They use non-locality the same way I do, which means in terms of quantum non-locality. Standard garden variety quantum theory is non-local AND respects signal locality.vanhees71 said:If there is no FTL signalling possible, then relativistic causality is preserved, i.e., in other words, there are no causal connections between space-like separated events possible, then relativistic causality is fulfilled. Maybe you have another definition for what you call "Einsteinian causality". Maybe what you in fact mean is not causality but determinism …
However, together with the fulfillment of the relativistic causality principle (i.e., no FTL signalling possible), …
You use nonlocality in two differwnt ways. One is the violation of Bell's inequality, and this is how it is used in all your references. The second that there is a causal relation between space-like events. You haven't cited a single paper that says that. Then you make the claim that the first implies the second and that experiments have proven the second. This is the reason for these debates. You don't claim that it is a posible explanation or that it is an interpretation you choose, but that it is an experimentaly proven fact.DrChinese said:I think you have cleared something up for me. You use the words “locality” and “non-locality” differently than most authors, including the most recent reference from Eisenberg et al: “The observed quantum correlations manifest the non-locality of quantum mechanics in spacetime.” They use non-locality the same way I do, which means in terms of quantum non-locality. Standard garden variety quantum theory is non-local AND respects signal locality.
You, on the other hand, choose to see locality only in terms of signal locality. If a theory respects signal, locality, then in your mind, it is a local theory. That viewpoint conflates two very different ideas. First, that no signal can exceed the speed of light. Second, that no action can occur that exceeds the speed of light, even if there’s no signal transmitted. As I say, quantum theory respects the first and rejects the second.
You have made a completely unwarranted assumption: that in the physical world, where signals cannot exceed c, that means no action can have distant consequences. And yet this experiment, and hundreds of others, state exactly the opposite: they demonstrate nonlocality and say so explicitly.
So, as per usual, I challenge you to provide suitable quotes from references other than yourself that support your position (as I have). I remain confident that you will ignore my challenge, to the same extent that you ignore the usage of these keywords by thousands of authors.
That's precisely the problem, I'd like to discuss in this thread. It's obviously impossible to discuss it without all the philosophical gibberish.DrChinese said:I think you have cleared something up for me. You use the words “locality” and “non-locality” differently than most authors, including the most recent reference from Eisenberg et al: “The observed quantum correlations manifest the non-locality of quantum mechanics in spacetime.” They use non-locality the same way I do, which means in terms of quantum non-locality. Standard garden variety quantum theory is non-local AND respects signal locality.
You are contradicting yourself repeatedly in this point since if the "first meaning" is fufilled, the "second meaning" follows. If there's no FTS signal propgation possible there cannot be causal influences between spacelike separated events. Local relativistic QFT respects both!DrChinese said:You, on the other hand, choose to see locality only in terms of signal locality. If a theory respects signal, locality, then in your mind, it is a local theory. That viewpoint conflates two very different ideas. First, that no signal can exceed the speed of light. Second, that no action can occur that exceeds the speed of light, even if there’s no signal transmitted. As I say, quantum theory respects the first and rejects the second.
They demonstrate strong correlations between far-distant parts of an entangle quantum systems. Is it really so difficult to understand the elementary difference between "causation" and "correlation"? All the experiments obviously demonstrate the opposite of what you say: E.g., the entanglement swap does not depend on the temporal order the measurement on photons (2,3) and photons 1 as well as 2 are performed. They may be even performed in no specific temporal order, i.e., such that the corresponding measurement events (i.e., the irreversible storage of the measurement results at far distant places) are space-like separated and thus have neither a definite temporal order nor are they causally connected within local relativistic QFT thanks of the assumption of the microcausality constraint.DrChinese said:You have made a completely unwarranted assumption: that in the physical world, where signals cannot exceed c, that means no action can have distant consequences. And yet this experiment, and hundreds of others, state exactly the opposite: they demonstrate nonlocality and say so explicitly.
I have not the time to quote again all the papers we discussed at length for years in this forum. If you want to understand the meaning of the QFT formalism, I recommend (in the order of sophistication)DrChinese said:So, as per usual, I challenge you to provide suitable quotes from references other than yourself that support your position (as I have). I remain confident that you will ignore my challenge, to the same extent that you ignore the usage of these keywords by thousands of authors.
From my stance I wonder, how do you distinguish between a locally generate "message" for signalling, from a local action that propagates into a remote disturbance?DrChinese said:You have made a completely unwarranted assumption: that in the physical world, where signals cannot exceed c, that means no action can have distant consequences.
I share the same view. There is no "classical reality" as you say, and it isn't my argument.vanhees71 said:Classicality is an emergent phenonmenon.
I really don't think this is the case. By introducing distinguishability, you've introduced a correlation with the environment that prohibits a determination of a Bell state suitable for selecting subensembles that would exhibit strong correlations between 1 and 4. Hence the mixture and the corresponding subensemble that only exhibits weak correlation.DrChinese said:Sure, the same detectors are present, and so that data becomes available just as when a swap occurs.
These type of statements (distant photons becoming entangled upon projection of the middle photons) can't be made rigorous under a minimalist interpretation. Events are analysed in terms of preparations, instrument settings, and correlations present in macroscopic data.It is also evidence that the first and last photons did not somehow share any entanglement before the projection of the middle photons.
DrChinese said:So, as per usual, I challenge you to provide suitable quotes from references other than yourself that support your position (as I have). I remain confident that you will ignore my challenge, to the same extent that you ignore the usage of these keywords by thousands of authors.
As expected, this challenge was clearly won by DrChinese. Of course, the question remains whether winning this challenge helps DrChinese's case in any way. Just because I can win against a weak opponent doesn't mean that I am strong. It is no secret that providing appropriate references is not a strength of vanhees71.vanhees71 said:I have not the time to quote again all the papers we discussed at length for years in this forum. If you want to understand the meaning of the QFT formalism, I recommend (in the order of sophistication)
S. Coleman, Lectures of Sidney Coleman on Quantum Field Theory,
...
S. Weinberg, The Quantum Theory of Fields, vol. 1,
...
A. Duncan, The conceptual framework of quantum field theory,
...
This book is complementary to Weinberg, discussing some important foundational topics, not covered by Weinberg (e.g., Haag's theorem, the impossibility of spontaneous symmetry breaking of gauge theories and Elitzur's theorem). In the foundations it's the same as Weinberg, also with the strong emphasis of the microcausality constraint.
I don't think this is correct. The quantum teleportation part seems to be what is important to DrChinese, the role of the Bell's inequality part for him seems to be just to verify that teleportation indeed took place.martinbn said:You use nonlocality in two differwnt ways. One is the violation of Bell's inequality, and this is how it is used in all your references. The second that there is a causal relation between space-like events.
Given that others seem to believe that "Causality" by Judea Pearl or "The Quantum Theory of Fields, vol. 1" by Steven Weinberg would be appropriate references, it feels strange to me to criticise DrChinese for not providing sufficiently appropriate references.martinbn said:You haven't cited a single paper that says that. Then you make the claim that the first implies the second and that experiments have proven the second. This is the reason for these debates. You don't claim that it is a posible explanation or that it is an interpretation you choose, but that it is an experimentaly proven fact.
C. H. Bennett, G. Brassard, C. Crépeau, R. Jozsa, A. Peres, and W. Wootters. Teleporting an unknown quantum state via dual classical and EPR channels. Phys. Rev. Lett., 70:1895–1899, 1993.Referee’s Report: Bennett et al., "Teleporting. . ." LZ4539
This is a charming, readable, thought-provoking paper. It presents a novel application of EPR correlations. The character of the quantum state (how much is inherent in the physical system, how much is a representation of our knowledge) is still an extremely elusive notion. This novel method for duplicating a quantum state somewhere else by a combination of quantum correlations and classical information will become an important one of the intellectual tools available to anybody trying to clear up this murkiness.
C. H. Bennett and S. J. Wiesner. Communication via one- and two-particle operators on Einstein-Podolsky-Rosen states. Phys. Rev. Lett., 69(20):2881–2884, 1992.Bennett and Wiesner, "Communication via one-and two-particle. . ." LT4749
Your question was: Does this qualify as "strikingly different" enough to publish? I have never read anything like it, and I have read a lot on EPR, though far from everything ever written. So as far as I know it is different.
But strikingly? The argument is very simple, so shouldn’t the point be obvious? After reading the paper I put it aside and spent the next week working hard on something totally unrelated. Every now and then I would introspect to see if some way of looking at the argument had germinated that reduced it to a triviality. None had. Last night I woke up at 3am, fascinated and obsessed with it. Couldn’t get back to sleep. That’s my definition of "striking".
So I say it’s strikingly different and I say publish it.
I don't understand, why you claim that the self-contradictory claims by DrChinese were victories against my arguments, which are simply based on standard relativistic QFT. That's quite ridiculus!gentzen said:In a certain sense, those are probably the wrong questions. The more interesting question seems to be why DrChinese prefers to score easy victories against vanhees71, instead of addressing the specific points brought up by Peter Donis, Morbert and others above? And the same goes for vanhees71: Why does he discuss locality of QFT with DrChinese, instead of addressing specific points brought up by Demystifier, A.Neumaier, and others elsewhere?
You have not read correctly what I wrote. The victory is just with respect to providing relevant references, not with respect to the argument itself. I explicitly addressed that point:vanhees71 said:I don't understand, why you claim that the self-contradictory claims by DrChinese were victories against my arguments, which are simply based on standard relativistic QFT. That's quite ridiculus!
gentzen said:Of course, the question remains whether winning this challenge helps DrChinese's case in any way. Just because I can win against a weak opponent doesn't mean that I am strong. It is no secret that providing appropriate references is not a strength of vanhees71.
If three thoroughly written textbooks about the subject are not relevant references, I don't know, what you want. Should I look for all the original papers of relativistic QFT? They are quoted in the standard textbooks anyway.gentzen said:You have not read correctly what I wrote. The victory is just with respect to providing relevant references, not with respect to the argument itself. I explicitly addressed that point:
Finally, a start of a reference. Always helps when a quote joins the reference. And it’s not really a paper at all. But it contains some reasonable and relevant discussion and is not too long a read. Quotes are in italics:Lord Jestocost said:“Quantum nonlocality vs. Einstein locality” by H. D. Zeh
https://www.thp.uni-koeln.de/gravitation/zeh/nonlocality.html
As per usual, your concept of quotes relates to entire books. That’s not a quote! There are many things presented in an entire book or paper. Be specific.vanhees71 said:If three thoroughly written textbooks about the subject are not relevant references, I don't know, what you want. Should I look for all the original papers of relativistic QFT? They are quoted in the standard textbooks anyway.
Also once more: The statements by DrChinese are self-contradictory. On the other hand he accepts the mathematical fact that relativistic, local QFT excludes causal connections between spacelike separated events. On the other hand he says there must be some in view of the Bell-test results. This is a contradiction, because the Bell-test results are precisely what's predicted by standard relativistic, loacal QFT, which excludes such causal connections!
DrChinese said:Finally, a start of a reference. Always helps when a quote joins the reference. And it’s not really a paper at all. But it contains some reasonable and relevant discussion and is not too long a read. Quotes are in italics:
Quantum theory is kinematically nonlocal, while the theory of relativity (including relativistic quantum field theory) requires dynamical locality ("Einstein locality"). How can these two elements of the theory (well based on experimental results) be simultaneously meaningful and compatible? How can dynamical locality even be defined in terms of kinematically nonlocal concepts?
So already, Zeh acknowledges QT is nonlocal in what he calls the kinematic sense. And that is different from relativistic sense of locality vs nonlocality, which he refers to as dynamical.
Dynamical locality in conventional terms means that there is no action at a distance: states "here" cannot directly influence states "there". Relativistically this has the consequence that dynamical effects can only arise within the forward light cones of their causes. However, generic quantum states are "neither here nor there", nor are they simply composed of "states here and states there" (with a logical "and" that would in the quantum formalism be represented as a direct product). Quantum systems at different places are usually entangled, and thus do not possess any states of their own. Therefore, quantum dynamics must in general describe the dynamics of global states. It may thus appear to be necessarily nonlocal.
This discrepancy is often muddled by insisting that reality is made up of local events or phenomena only. However, quantum entanglement does not merely represent statistical correlations that would represent incomplete information about a local reality. Individually observable quantities, such as the total angular momentum of composed systems, or the binding energy of the He atom, can not be defined in terms of local quantities. This nonlocality has been directly confirmed by the violation of Bell's inequalities or the existence of Greenberger-Horne-Zeilinger relations. If there were kinematically local concepts completely describing reality, they would indeed require some superluminal "spooky action at a distance" (in Einstein's words). Otherwise, however, such a picture is questionable or meaningless. In particular, nothing has to be teleported in so-called quantum teleportation experiments. In terms of nonlocal quantum states, one has to carefully prepare an appropriate entangled state that contains, among its components, all states to be possibly teleported (or their dynamical predecessors) already at their final destination…
These kinematical properties characterize quantum nonlocality. But what about Einstein locality in this description?
So although he describes the situation in somewhat different terminology than I would, we agree that quantum theory is quantum nonlocal, which has been directly confirmed.
From Zeh’s other page:
Accepting the physical reality of nonlocal entangled quantum states eliminates any need for spooky action at a distance, and in particular for any advanced action that seems to occur in a delayed choice experiment. This delayed choice simply determines which property of the controllably entangled wave function that has unitarily arisen in a virtual "measurement" is finally irreversibly ("really") measured. Paradoxes arise only if one attempts to describe quantum physics exclusively in local terms.
Here Zeh essentially says: take your choice, it’s either nonlocality or spooky action at a distance you must accept. I don’t have any issue with this view at all, I use the terms interchangeably anyway. We either have a nonlocal quantum context, or there is action (interplay) between the distant components. No meaningful (predictive) difference between the 2 views in my book, so label as you prefer. You say there is a single nonlocal context, or a group of local contexts that exhibit action at a distance. Same thing. In both cases, signal locality is respected.
So I generally agree with Zeh’s analysis in the above. He does discuss the QFT microcausality condition, which he sees as a) not contradicting the above; and b) referring to that which respects relativistic signal locality.
If you say QM is nonlocal (as hundreds of papers say verbatim, and you seem to agree with) but there is no action at a distance: Ok. I just never hear you or others admit that essential point loud and clear. Just say QFT is nonlocal! As I have pointed out repeatedly: the experimenter’s choice to execute a swap here objectively (ie experimentally proven) changes the state of unrelated distant photons to an entangled one, which did not previously exist. (Without any debate on my part, that nonlocal swap cannot be detected without a classical signal.)mattt said:The mathematics and experimental results have always been clear.
The problems or disagreements arise only when we (different people) try to describe it all in English or in any other human language.
I quite like the way this article describe in English the whole situation.
He uses the term "kinematically nonlocal" as a synonym of "existence of quantum entangled states" which is a synonym of "existence of states that violate Bell-type inequalities".
Me, vanhees, martinb, Cthunga, Morbert, gentzen and just about everybody obviously accept this, and we have never disputed it.
He also says that accepting the physical reality of these entangled quantum states (which we all obviously accept, because the mathematics say so, and the experiments confirm it) eliminates any need for spooky action at a distance, (and in particular for any advanced action that seems to occur in a delayed choice experiment).
This is exactly what I (and many others here) have been saying for months. You don't need any instant action at a distance to describe these experiments.
If anything, this article seem to describe the whole situation almost exactly the same way as we have been describing it for months here.
It is you (and perhaps some others as well) who insists in the necessity of accepting nonlocal causation (actions here instantly affecting physical things there) as the only way to describe these type of experiments.
Morbert said:A) I really don't think this is the case. By introducing distinguishability, you've introduced a correlation with the environment that prohibits a determination of a Bell state suitable for selecting subensembles that would exhibit strong correlations between 1 and 4.
B) Perhaps a skilfull experimentalist can carry out a measurement that projects onto a pure Bell state after distinguishability has been established…
A) introducing a time delay, as was done in the experiment, does not change which detectors are triggered. there is no change to the interaction with the environment whatsoever. What you end up with is an indication of which Bell State would’ve been selected if one had been created.Morbert said:C) These type of statements (distant photons becoming entangled upon projection of the middle photons) can't be made rigorous under a minimalist interpretation.
I'm not sure this claim is justified. If the incoming 2 & 3 photons are distinguishable, no swap is produced; and that means you cannot make counterfactual claims about what would have happened if a swap had been produced. All you can say is that, for that particular run, no swap was produced. The 2 & 3 photon measurements at the output of the BSM apparatus are measurements of non-entangled photons and give no information about photons 1 & 4.DrChinese said:What you end up with is an indication of which Bell State would’ve been selected if one had been created.
It's the significance of the detector trigger that is changed. To illustrate this, consider an abstract bell measurement circuit involving a CNOT (CN) state, a Hadamard (H) gate, and spin-z measurements (M)DrChinese said:A) introducing a time delay, as was done in the experiment, does not change which detectors are triggered. there is no change to the interaction with the environment whatsoever. What you end up with is an indication of which Bell State would’ve been selected if one had been created.
Morbert said:It's the significance of the detector trigger that is changed. To illustrate this, consider an abstract bell measurement circuit involving a CNOT (CN) state, a Hadamard (H) gate, and spin-z measurements (M)
View attachment 330458
We can see that an input ##|\Phi^+\rangle## will yield $$|\Phi^+\rangle \xrightarrow[\text{CN}]{} \frac{1}{\sqrt{2}}\left(|0\rangle+|1\rangle\right)|0\rangle\xrightarrow[\text{H}]{}|00\rangle\xrightarrow[\text{M}]{} M_{00}$$I.e. We infer a bell state from the reading 00. But now lets say our input is the state $$\frac{1}{2}\left(|\Phi^+\rangle\langle\Phi^+|+|\Phi^-\rangle\langle\Phi^-|\right) = \frac{1}{2}\left(|00\rangle\langle00|+|11\rangle\langle11|\right)$$Now we have the evolution
$$\frac{1}{2}\left(|00\rangle\langle00|+|11\rangle\langle11|\right)\xrightarrow[\text{CN}]{}\frac{1}{2}\left(|00\rangle\langle00|+|10\rangle\langle10|\right)\xrightarrow[\text{H}]{}\frac{1}{2}\left(|00\rangle\langle00|+|10\rangle\langle10|\right)\xrightarrow[\text{M}]{}\frac{1}{2}\left(M_{00}+M_{10}\right)$$You can see that a mixed state has a 50/50 chance of triggering a detector result 00.
Morbert said:And so we are not automatically justified in inferring a Bell state from the same detector outcomes.* I suspect something similar (but not identical) is happening in the actual experimental setup. Distinguishing photons leaves the phase undefined, and so instead of inferring a bell state from detectors, a mixed "correlated" state is inferred.
You have it backwards though! If there is no Bell state, there is no swap. Phase information is perfectly available but not meaningful when a swap does not occur. That because the 1,2 pair does not develop a relationship with the 3,4 pair.Morbert said:If we do not have phase information, we cannot infer a bell state from a set of detector outcomes
Of course, if you are unwilling to read large parts of a textbook to understand the details of a theory, I can't help you.DrChinese said:As per usual, your concept of quotes relates to entire books. That’s not a quote! There are many things presented in an entire book or paper. Be specific.
QFT requires and ensures signal locality, and that's all what locality means. There is no non-local action. At least there's no experiment demonstrating this, and I don't know a single reference that claims this. To the contrary locality in the sense of relativistic QFT is envoked as an argument in Bell tests that there are NO causal connections between the measurements at far distant places, i.e., a large effort is taken to ensure that experiments like teleportation or entanglement swapping etc. are constructed such that the measurement events or even the choice of the measured observables at the far distant places are space-like separated, and then it's argued that there cannot be causal influences among these manipulations at far distant places.DrChinese said:I am not self contradictory; you just can’t see any options other than an entrenched position.
Specifically: sure I agree that QFT requires signal locality. And sure I agree that nonlocal action requires a classical signal to perceive. But there is nonlocal action as all of the references say. No paper says anything different.
An experimenter's choice does not need to have deterministic outcome. That's the whole point: The freedom is in the choice of the observable to be measured. Depending on the state these observable may not take a predetermined value before the measurement and that's why the outcome in general is random, and given such a preparation the experimenter cannot choose, what the outcome of the measurement of this observable will take. All this has indeed nothing to do with locality or non-locality. Also non-relativistic QT, which does not fulfill the relativistic locality constraints, is a consistent theory, but it's not describing Nature in all situations while relativistic local QFT does.DrChinese said:Quantum contexts/events/actions are generally probabilistic as to outcomes. That’s true whether the contexts are local or nonlocal. If you use the word “causal” to describe an experimenter’s choice which must have a determined specific outcome (such as a specific bell state): then yes, QFT would be locally causal - precisely because experiments do not allow the experimenter the opportunity to make that choice.
Yes, but the selection of the subensemble is due to local measurements, which do not causally influence the other two photons which are far distant. The entanglement swap is possible due to the entanglement of the pairs 12 and 34. The entanglement of the subensemble generated by projecting the photons (23) to a Bell state is due to the preparation of the full ensemble in the state, where photons (12) and (34) were both maximally entangled. That is the predition of relativistic local QFT. It's known since 1928 that relativistic QM is not a consistent theory exactly for the reason that it does not obey the causality constraints a relativsitic theory has to obey! That's why Dirac was forced to his hole-theoretical reinterpretation of his equation and thus the introduction of anti-particles. This hole theory is conceptually problematic but nevertheless equivalent to QED, and QED is conceptually much less problematic, because from the outset it assumes the possibility of annihilation and creation processes and realizes the causality constraint via microcausality of local observable-operators.DrChinese said:But neither I nor most authors require such a strict view when discussing these experiments. Quantum theory predicts an experimenter can choose to execute a swap here and objectively change the state of a pair that is distant. That change is to a state that is randomly occurring, itself outside the control of the experimenter. Further, the experimenter can make his choice before or after 1,4 pair detection. In my book, that’s a violation of strict Einsteinian causality. But of course… not a violation of most tenets of special relativity. That being quantum predictions of relativistic QM.
I think the choice of vocabulary makes things hard to follow, particularly the parts in bold. For example, when you say "if there is no Bell state, there is no swap" do you mean, "when the instrument that measures the middle photons is set such that it projects onto a mixed state rather than a pure bell state, the corresponding subensembles of experimental runs will not exhibit Bell-inequality-violating inequalities between measurements on the 1,4 pair? If yes then I completely agree. So e.g.DrChinese said:You have it backwards though! If there is no Bell state, there is no swap. Phase information is perfectly available but not meaningful when a swap does not occur. That because the 1,2 pair does not develop a relationship with the 3,4 pair.
But for those of you out there that don’t believe anything physical happens at the 2,3 measurement that creates the 1,4 entanglement: what difference would that make? As I indicated, the detectors indicate Reflect/Transmit at the projecting splitter and the polarization. What you call phase is simply part and parcel of those same properties.
Seen another way: tell me what happens to 1,4 as a result of a successful swap where the 2,3 photons come close to each other - as opposed to when a delay is introduced and no swap occurs. The coincidence time window has most 2,3 photons detected within 3 ns and usually 1 ns apart. 1 ns is about 1 foot. So they do not precisely overlap. Further, orthogonal photons cannot interact (and that happens in 1/2 the cases). So explain what is different when a delay is inserted to change any readings when our experimenter flips his swap/no swap switch.
If our instruments are set such that a measurement on the middle photons is characterised by a projection onto a Bell state, then, after all experimental runs are complete, we can divide our experimental runs into subensembles in accordance with the Bell-state measurement outcomes, and at least two of these subensembles will show Bell-inequality-violating correlations between measurements on 1 and 4.Seen another way: tell me what happens to 1,4 as a result of a successful swap where the 2,3 photons come close to each other - as opposed to when a delay is introduced and no swap occurs.
Morbert said:I think the choice of vocabulary makes things hard to follow, particularly the parts in bold. For example, when you say "if there is no Bell state, there is no swap" do you mean, "when the instrument that measures the middle photons is set such that it projects onto a mixed state rather than a pure bell state, the corresponding subensembles of experimental runs will not exhibit Bell-inequality-violating inequalities between measurements on the 1,4 pair? If yes then I completely agree. So e.g. If our instruments are set such that a measurement on the middle photons is characterised by a projection onto a Bell state, then, after all experimental runs are complete, we can divide our experimental runs into subensembles in accordance with the Bell-state measurement outcomes, and at least two of these subensembles will show Bell-inequality-violating correlations between measurements on 1 and 4.
If instead our instruments are set such that a measurement of the middle photons fails to project onto a Bell-state, we can no longer use the protocol that divides our experimental runs into subensembles that show Bell-inequality-violating correlations between 1 and 4. "No projection onto a Bell state, no protocol for selecting subensembles with bell-inequality-violating correlations."
Exactly, and that's also a very important point. If you do another measurement with 2&3 to select a subensemble, you simply get a different subensemble, which doesn't tell you anything about what might have happened, if you'd do the projection to a Bell state. There is no "counterfactual definiteness", as the quantum-foundationalists call it. To say it simpler with Mermin: QT doesn't tell anything about unperformed experiments. That's already the trap, EPR get caught in.Morbert said:I think the choice of vocabulary makes things hard to follow, particularly the parts in bold. For example, when you say "if there is no Bell state, there is no swap" do you mean, "when the instrument that measures the middle photons is set such that it projects onto a mixed state rather than a pure bell state, the corresponding subensembles of experimental runs will not exhibit Bell-inequality-violating inequalities between measurements on the 1,4 pair? If yes then I completely agree. So e.g. If our instruments are set such that a measurement on the middle photons is characterised by a projection onto a Bell state, then, after all experimental runs are complete, we can divide our experimental runs into subensembles in accordance with the Bell-state measurement outcomes, and at least two of these subensembles will show Bell-inequality-violating correlations between measurements on 1 and 4.
If the measurement on the pair 2&3 fails for some reason, we can't select it to form the subensembles you want to select in this experiment. Then you simply can't use this specific realization of the procedure at all. That's one of the loop holes, i.e., that you always have a finite probability that there's no definite outcome. E.g., real-world photon detectors have a finite probability to simply fail to detect a photon going through them. This may open the possibility that there's some specific "hidden variable" determining systematically this detector failure and only the photons that get detected behave as predicted by QT. This loophole is pretty well closed by constructing ever better photon detectors.Morbert said:If instead our instruments are set such that a measurement of the middle photons fails to project onto a Bell-state, we can no longer use the protocol that divides our experimental runs into subensembles that show Bell-inequality-violating correlations between 1 and 4. "No projection onto a Bell state, no protocol for selecting subensembles with bell-inequality-violating correlations."
Morbert said:If our instruments are set such that a measurement on the middle photons is characterised by a projection onto a Bell state, then, after all experimental runs are complete, we can divide our experimental runs into subensembles in accordance with the Bell-state measurement outcomes, and at least two of these subensembles will show Bell-inequality-violating correlations between measurements on 1 and 4.
So what you’re saying is: the success or failure of the BSM doesn’t change anything for the remote (1,4) pairs (while I say it creates the entanglement); but a swap the experimenter chooses to fail messes up the BSM protocol results. By what logic is the something physical occurring between 2,3 pairs that are orthogonal? Because that is detected regardless of whether the swap succeeds! Are you seriously asserting that adding a delay can change the outcome of the polarization portion of the BSM protocol?Morbert said:If instead our instruments are set such that a measurement of the middle photons fails to project onto a Bell-state, we can no longer use the protocol that divides our experimental runs into subensembles that show Bell-inequality-violating correlations between 1 and 4. "No projection onto a Bell state, no protocol for selecting subensembles with bell-inequality-violating correlations."