Local realism ruled out? (was: Photon entanglement and )

[ZapperZ]

It is possible, but not with absolute certainty. This is because the detectors have a very low efficiency, so the experimental statistics refers to a very small sample of actual particles. In principle, it is possible that this small sample is not a typical sample, but a sample with very special properties, making the illusion of violation of Bell inequalities. Nobody knows a good reason why this sample would not be a typical one, yet such a possibility in principle exists.

This is like president elections. Before the actual counting of all votes, usually there is a preliminary counting of a small sample of all votes. Usually it is a good representative of all the votes, yet the victory of one president candidate over the other cannot be proclaimed before the actual counting of all (or at least of the majority of all) votes.

Akhmetely is like a president candidate who believes that he will win the elections even though all statistics on small samples say the opposite. It's true, such a president candidate may still win, but statistically it is very unlikely.

Good analogy, but here's the second half of it.

Say that you DO ask all the citizens to vote, but not officially, i.e. not by casting it in a ballot on election day. For example, you got every single citizen to be at a voice caucus before the actual election. And they vote for the president. So you got the vote of every single citizen.

Yet, again, he refuses to accept the vote because this time, it is not an "official" vote because he said that between this caucus and the actual voting day, someone could change his/her mind.

This is what is going on with the EPR-type experiment using charge particles, where the detection efficiency is 100%. The only drawback here is that they still have not been able YET to close the locality loophole (and I fully expect that they will soon!). That's why I mentioned earlier that these loopholes are closed separately in different experiments. It is like you get the SAME result no matter if you only do a "sample election", or if you do a caucus of 100% of the citizen. What are the odds that if you do not win on any of those, that you will win if 100% of the citizen voted on election day? We live our lives with significantly lower odds than that!

Zz.

 

[Dmitry67]

Thank you
What also puzzles me is the motivation of that group of "diehard localists". There are no people who deny SR and other modern theories seriously, except few crackpots.

The only 2 exceptions I know are: MOND and LR. Why locality is so important for these people that they won' accept the nonlocality no matter what?

 

[Demystifier]

Zz, thanks for the second half. Can you give me a reference for the EPR-type experiment using charged particles with the 100% detection efficiency?
(If you already did it on some post above, you can only write the post number.)

 

[ZapperZ]

Zz, thanks for the second half. Can you give me a reference for the EPR-type experiment using charged particles with the 100% detection efficiency?
(If you already did it on some post above, you can only write the post number.)

I've mentioned several, but it'll take too long to hunt for them on here. But here's a couple of references that I have handy:

S. Olmschenk et al., Science v.323, p.486 (2009).
D.N. Matsukevich et al., PRL v.100, p.150404 (2008).

Zz.

 

[Demystifier]

I've mentioned several, but it'll take too long to hunt for them on here. But here's a couple of references that I have handy:

S. Olmschenk et al., Science v.323, p.486 (2009).
D.N. Matsukevich et al., PRL v.100, p.150404 (2008).

Zz.

Thanks! The paper is available for free:
http://www.sciencemag.org/cgi/reprint/323/5913/486.pdf?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=olmschenk&searchid=1&FIRSTINDEX=0&resourcetype=HWCIT

However, from the title and the abstract it is not obvious that this paper closes the fair sampling loophole of nonlocality. Do you know a paper which states it more explicitly?

EDIT: Now I've noticed that you added a PRL reference. It is more explicit. This is exactly what I needed. Thanks again.

 

[zonde]

There are in fact hundreds of experimental violations of "genuine" Bell Inequalities. There is no hole in the GHZ no-go.

There is exactly the same fair sampling hole in GHZ.
Basically Bell theorem says you can't get different correlations predicted by QM using the same pairs. That is exactly the same with GHZ. Only in GHZ this is purer as you have group of four correlations where one of them falls out if you assume the same detected pairs for all correlations.

And how can a hole in a no-go theorem be evidence for locality anyway? That doesn't even make sense.

That's right. Failure of disproof is a failure. It can't be proof of something else.

Please explain how photons that are not - and have never been - in each other's light cones can become entangled. According to local realism, that should not be possible. I notice that no matter where this thread goes, you avoid these difficult questions, and resort to the weakest references as part of your hand waving.

Your implied reference to the experiment you quoted earlier is quite poor.
If you read this article you can easily find out that it's claim is seriously biased. While if you somehow imagine that photons appear from nowhere you might claim that but in that case you are very far off not only from local realism but from SQM too.
To confirm that you just have to note that tuning condition for experiment is observation of Hong–Ou–Mandel dip.

 

[DrChinese]

1. There is exactly the same fair sampling hole in GHZ.


2. Your implied reference to the experiment you quoted earlier is quite poor.
If you read this article you can easily find out that it's claim is seriously biased. While if you somehow imagine that photons appear from nowhere you might claim that but in that case you are very far off not only from local realism but from SQM too.
To confirm that you just have to note that tuning condition for experiment is observation of Hong–Ou–Mandel dip.

1. That would be news to a lot of people. Fair sampling is NOT assumed. You theoretically only need a sample size of 1, as this is essentially an all-or-nothing test. In practice, of course, there is a sample of events and the results are not perfect. But the answer is still the same: the predictions of QM are supported and LR are rejected. And Fair Sampling is not a part of the experiment.

2. Zeilinger? Are you serious? If that doesn't work, I am not sure who I would need to present.

 

[zonde]

D.N. Matsukevich et al., PRL v.100, p.150404 (2008).

http://arxiv.org/abs/0801.2184"
"We observe violation of a Bell inequality between the quantum states of two remote Yb+ ions separated by a distance of about one meter with the detection loophole closed. The heralded entanglement of two ions is established via interference and joint detection of two emitted photons, whose polarization is entangled with each ion. The entanglement of remote qubits is also characterized by full quantum state tomography."
As I understand it states that emitted photons of two ions interact and as a result two ions become entangled (entanglement teleportation) and as a result the same photons that where used to entangle ions instantaneously show signs of ion entanglement (result of entanglement is telported back to photons). And then these photons are detected. Right?

Interesting but it is quite unclear what it has to do with local realism.

 

[Demystifier]

1. That would be news to a lot of people. Fair sampling is NOT assumed. You theoretically only need a sample size of 1, as this is essentially an all-or-nothing test. In practice, of course, there is a sample of events and the results are not perfect. But the answer is still the same: the predictions of QM are supported and LR are rejected. And Fair Sampling is not a part of the experiment.

Do the authors of the paper reporting the actual GHZ experiment explicitly claim that this disproof of LR does not contain any experimental loopholes?

 

[SpectraCat]

1. That would be news to a lot of people. Fair sampling is NOT assumed. You theoretically only need a sample size of 1, as this is essentially an all-or-nothing test. In practice, of course, there is a sample of events and the results are not perfect. But the answer is still the same: the predictions of QM are supported and LR are rejected. And Fair Sampling is not a part of the experiment.

2. Zeilinger? Are you serious? If that doesn't work, I am not sure who I would need to present.

Zonde's criticism is actually a reasonable one, and is not really addressed in the paper. The fact is that the pump photons for this experiment come from the same source, and an interferometer is actually part of the experimental scheme upstream of the two independent PDC's. Therefore, I think any claim that the two initial entangled pairs in this experiment are "independent" needs to be very carefully examined. I have been thinking about this since zonde first mentioned this criticism a few weeks ago, and I have not been able to disprove or rectify it. I definitely don't think it can be dismissed out of hand.

I would like to see a version of this experiment that uses two independent pump lasers ... but that is quite technically challenging from a synchronization point of view. There are also non-trivial issues concerning how "identical" the pump pulses are in such a case, because distinguishability of the B & C photons could (would?) disrupt the entanglement swapping. That last point in particular is why I think zonde's criticism is deserving of very careful analysis.

 

[zonde]

1. That would be news to a lot of people. Fair sampling is NOT assumed. You theoretically only need a sample size of 1, as this is essentially an all-or-nothing test. In practice, of course, there is a sample of events and the results are not perfect. But the answer is still the same: the predictions of QM are supported and LR are rejected. And Fair Sampling is not a part of the experiment.

Theoretically LR was ruled out by Bell theorem.
And no you can't do that with sample size of 1. You need 4 experiments (with sample size of 1):
- one channel H/V, other L/R, third L/R
- one channel L/R, other H/V, third L/R
- one channel L/R, other L/R, third H/V
- one channel H/V, other H/V, third H/V
or if we can't do H/V and L/R simultaneously then even 8 experiments.

2. Zeilinger? Are you serious? If that doesn't work, I am not sure who I would need to present.

No, not Zeilinger. See post #219 where I gave the quote (and link to paper):
https://www.physicsforums.com/showthread.php?p=2590786#post2590786"
That is the same paper you discussed in other thread.

 

[zonde]

What also puzzles me is the motivation of that group of "diehard localists". There are no people who deny SR and other modern theories seriously, except few crackpots.

The only 2 exceptions I know are: MOND and LR. Why locality is so important for these people that they won' accept the nonlocality no matter what?

Oh, that is somewhat irrational feelings toward consistent overall picture.
I believe that this consistency it is a requirement to use intuition fully.

And SR is consistent - there are no contradictions with more intuitive neo-Lorentzian interpretation.

 

[Dmitry67]

Oh, that is somewhat irrational feelings toward consistent overall picture.
I believe that this consistency it is a requirement to use intuition fully.

And SR is consistent - there are no contradictions with more intuitive neo-Lorentzian interpretation.

well, yes, but:
* there is no alternative suggested by local realists. there are no neo-LR interpretations to compare with. Even MOND curvefitting, no matter how naive is it, is better: at least, it is something.
* Why intuition insists on locality? Mine does not.

 

[Demystifier]

* Why intuition insists on locality? Mine does not.

Mine too. For example, the Newton law of gravity is quite intuitive to me. Also, when I was a little child, I thought that light and sound come to me from their source instantaneously.

 

[DrChinese]

Zonde's criticism is actually a reasonable one, and is not really addressed in the paper. The fact is that the pump photons for this experiment come from the same source, and an interferometer is actually part of the experimental scheme upstream of the two independent PDC's. Therefore, I think any claim that the two initial entangled pairs in this experiment are "independent" needs to be very carefully examined. I have been thinking about this since zonde first mentioned this criticism a few weeks ago, and I have not been able to disprove or rectify it. I definitely don't think it can be dismissed out of hand.

I would like to see a version of this experiment that uses two independent pump lasers ... but that is quite technically challenging from a synchronization point of view. There are also non-trivial issues concerning how "identical" the pump pulses are in such a case, because distinguishability of the B & C photons could (would?) disrupt the entanglement swapping. That last point in particular is why I think zonde's criticism is deserving of very careful analysis.

It is true that the same pump is being used in the referenced experiment. But subseqently, Zeilinger has put together a method of synchronizing separate lasers. Nothing changes when the proper setup is used and the photons are indistinguishable - as would be expected from QM. I think it is only a matter of time before all of the separate elements can be assembled into a single experiment. I would agree that it is always desirable to run the experiment with all the refinements together, where possible and practical.

http://arxiv.org/abs/0809.3991

In the above, there is entanglement swapping but there is no attempt (as I recall) to also perform delayed choice.

 

[DrChinese]

Theoretically LR was ruled out by Bell theorem.
And no you can't do that with sample size of 1. You need 4 experiments (with sample size of 1):
- one channel H/V, other L/R, third L/R
- one channel L/R, other H/V, third L/R
- one channel L/R, other L/R, third H/V
- one channel H/V, other H/V, third H/V
or if we can't do H/V and L/R simultaneously then even 8 experiments.


No, not Zeilinger. See post #219 where I gave the quote (and link to paper):
https://www.physicsforums.com/showthread.php?p=2590786#post2590786"
That is the same paper you discussed in other thread.

OK, Tittel & Gisin et al. I guess I am missing what you are saying, because you cannot be questioning these folks' conclusions.

 

[akhmeteli]

You might say the signal locality is evidence of locality, but the rest of what you say is wrong - again. If you want to reject evidence that goes against your personal opinion, please do not label it as science. Just call it for what it is: a quasi-religious view.

With all due respect, if you declare something wrong, it does not necessarily mean it is indeed wrong. I discuss your specific arguments below.

There are in fact hundreds of experimental violations of "genuine" Bell Inequalities.

There are none. Nil. Gimme a break, or a reference to experimental violations without loopholes.

There is no hole in the GHZ no-go.

Does not it use the QM theory of measurement?

And how can a hole in a no-go theorem be evidence for locality anyway? That doesn't even make sense.

If you think that a no-go theorem with a hole is a proof of nonlocality, then a hole in that theorem is certainly a proof of locality. I could agree that a hole is not a proof of locality, but not before you agree that a theorem with a hole is not a proof of nonlocality. This is a zero-sum game, and I believe the rules should be the same for proponents of both views.

Please explain how photons that are not - and have never been - in each other's light cones can become entangled.

First of all, I said several times that entanglement per se does not spell nonlocality (if you disagree, and you seem to disagree, the burden of proof is on you - I reject your "by definition" argument - indeed, if, for example the entangled particles are not spatially separated, they are no problem for locality, so don't tell me about definitions), so I don't need to explain anything. You can only declare nonlocality if the Bell inequalities are violated, and there is no evidence of violations of the genuine Bell inequalities. If you deny that, this is just your personal theory.

Ok, so, as I said, I am under no obligation to explain entanglement. However, I can repeat the following: "QFT-like unitary evolution in Hilbert space (which, by the way, seems to describe entanglement as well) may be just a disguise for nonlinear partial differential equations (you may wish to look at the very brief outline of the relevant published results of other people in my post https://www.physicsforums.com/showpost.php?p=1825523&postcount=90." So we have nonlinear differential equations in 3+1 dimensions, which are local, as input, use the referenced mathematical trick, and get something looking very much like quantum field theory, but equivalent to the input local equations on the set of solutions of those local equations. But now you have linear evolution equations in the Fock space, so there could be at least an appearance of entanglement. Again, I did not explore this much further as a local explanation of entanglement, but this does look like a possibility.

According to local realism, that should not be possible.

Sez who? See above.

I notice that no matter where this thread goes, you avoid these difficult questions, and resort to the weakest references as part of your hand waving.

Look, in this post I had to pretty much repeat myself, that means I did not "avoid these difficult questions" previously.

 

[akhmeteli]

Ok, so I think I finally understand why it has been to hard to understand your point of view here, at least in my case. You are actually challenging the foundations of the standard formulation of quantum mechanics, by attacking one of the core postulates. This is of course fine, but it would have been helpful if you constructed your arguments in that context from the beginning, rather than focusing on the Bell theorem, which is actually just collateral damage from your primary attack.

I regret that I was not able to make my posts easier to understand.

In truth, there is nothing wrong with Bell's theorem, because he simply takes for granted the postulates that are part and parcel of SQM ... that is what one is *supposed* to do with postulates, when working within a theoretical framework. On the other hand, you refuse to accept one of those postulates, as you have stated consistently from the beginning, and of course this is the really the only logical grounds on which to challenge an otherwise correct mathematical proof/derivation.

I agree on these points.

EDIT: As I said above, this is fine, but it is hardly mainstream in this case. While the "measurement problem" has been debated long and hard in quantum mechanics, I think most people would still concede that this has not so far proved to be a practical problem for either measurements, or for theoretical predictions derived from the accepted postulates.

I'd say it is not the mainstream in the sense that few people care about it. On the other hand, not many people deny there is a problem. For example, DrChinese does not deny this. So in this sense you may perhaps say it is the mainstream. You may also wish to look at the Schlosshauer quote at the end of my post 41 in this thread.

So, while I tend to view your challenge to SQM as rather quixotic, who is to say that I am correct?

Quixotic? I don't know. Well, sometimes even I think that there should be less painful ways to make friends:-) On the other hand, I think my arguments are pretty straightforward, so many people do understand them, like you understood them. You did not become a local realist, you still think Nature is nonlocal, we still disagree, but you just understood my arguments, and I think this is good for both of us. You see, I am not even sure I can call myself a local realist: indeed, if tomorrow experiments prove me wrong, so be it, I'll have to change my views.

Actually, I guess you would say nightlight is quixotic as well, but I am grateful to him, as he made clear some things that looked totally mysterious.

All I can say is that the postulates of SQM have served us rather well to this point, and there are no clear-cut cases where they have been found to be false. Perhaps there is a point to be made that they are somehow self-contradictory, but so far that is not a widely held view. I have no problem "rationalizing away" the seeming contradiction that you raise, because the unitary evolution postulate pertains to the microscopic quantum system, whereas the measurement postulate pertains to the interaction of the quantum system with a macroscopic detector. Thus the apparent irreversibility that seems to be the focus of your concerns could in my view just be an "effective irreversibility" resulting from entropic effects as the quantum system interacts with the (effectively) continuous distribution of states represented in the macroscopic detector. I think that if this is correct (and I am not claiming that it is), it would be provide a nice symmetry with classical physics, where temporal irreversibility is also just an "effective" phenomenon resulting from the tendency of natural systems to seek states of high entropy.

Neither would I have problems "rationalizing away" the contradiction, but it introduces nonlocality, and that is a really radical notion. I do need iron-clad arguments to accept it.

 

[Count Iblis]

How does this all square with the fact that I'm unquestionably real and local?

 

[Frame Dragger]

How does this all square with the fact that I'm unquestionably real and local?

Are you?

 

[ThomasT]

... how can you be so sure that the first set of polarizers breaks the entanglement? As far as I can tell, the only thing that can be said for sure is that detection of one member of an entangled pair breaks the entangled state, and I don't think it has been proven that interaction with a polarizer is the same as detection. (Actually, I would be happy if the polarizer interactions were proven to be equivalent to detection, because it would drastically strengthen my position in an argument with DrChinese that I have been having in another thread!)

In the entangled state polarization is undetermined and QM just specifies the relationship between the counter-propagating disturbances incident on the polarizers.

Afaik, when polarization is determined, then entanglement is broken. The polarization is determined by the polarizer via transmission along its axial setting.

 

[ThomasT]

Why intuition insists on locality? Mine does not.

Instantaneous propagation is a contradiction in terms.

FTL propagation is not demonstrated.

QM projection along transmission axis of polarizer transmitting detected disturbance is based on assumption of local common cause.

There are only two values for angular difference of polarizers wrt which A and B are perfectly correlated (anticorrelated). These correlations at these settings have a local common cause explanation. There are no other A<->B correlations to explain.

The coincidental detection angular dependency can be reproduced via LHV formulation.

What's the intuitive support for nonlocality?

Imho, nonlocality only exists via the manipulation of terms and misinterpretation.

 

[Frame Dragger]

Instantaneous propagation is a contradiction in terms.

FTL propagation is not demonstrated.

QM projection along transmission axis of polarizer transmitting detected disturbance is based on assumption of local common cause.

There are only two values for angular difference of polarizers wrt which A and B are perfectly correlated (anticorrelated). These correlations at these settings have a local common cause explanation. There are no other A<->B correlations to explain.

The coincidental detection angular dependency can be reproduced via LHV formulation.

What's the intuitive support for nonlocality?

Imho, nonlocality only exists via the manipulation of terms and misinterpretation.

IMHO Most people, myself included, believe that your viewpoint only exists through those means in bold; I might add a forcefully willful ignorance that borders on the religious.

 

[Dmitry67]

For me no-FTL and locality is something which emerges only macroscopically. So locality, while it is observed in most cases and is only "weakly" violated in EPR is not "natural"

 

[akhmeteli]

1. That would be news to a lot of people. Fair sampling is NOT assumed. You theoretically only need a sample size of 1, as this is essentially an all-or-nothing test. In practice, of course, there is a sample of events and the results are not perfect. But the answer is still the same: the predictions of QM are supported and LR are rejected. And Fair Sampling is not a part of the experiment.

DrChinese,

I admit that I don't know much about GHZ. However, in the article by Zeilinger e.a., Nature 403, 515-519 (3 February 2000),
Experimental test of quantum nonlocality in three-photon Greenberger–Horne–Zeilinger entanglement, I found the following quote:
"However, we realize that, as for all existing two-particle tests of local
realism, our experiment has rather low detection efficiencies.
Therefore we had to invoke the fair sampling hypothesis21,22,
where it is assumed that the registered events are a faithful
representative of the whole."
So, at least on the face of it, fair sampling is used in GHZ experiments. Of course, the article is relatively old. However, in the following article (GHZ and Shimony, Bell's theorem without inequalities, Am. J. Phys., 58 (12), 1990) I found the following: (the authors discuss a possible GHZ experiment):
"The second step is to show how the test could be done even with low-efficiency detectors, provided that we make a plausible auxiliary assumption, which we call fair sampling. Finally, we show that the auxiliary assumption is dispensable if detector efficiencies exceed 90.8%." So it looks like you need 90% efficient detectors to do without fair sampling in GHZ. To the best of my knowledge, there are no such optical detectors. Please advise if I am wrong.

As for your latest reference (12.4 km experiment), the authors seem to be remarkably reticent on the issue of absence/presence of loopholes.

Another thing. At http://www.quantum.at/fileadmin/Presse/2008-07-01-MG-PW_A_Quantum__Renaissance.pdf Aspelmeyer and Zeilinger (Physics World July 2008, p. 22) write the following:

"But the ultimate test of Bell’s theorem is still missing:
a single experiment that closes all the loopholes at once.
It is very unlikely that such an experiment will disagree
with the prediction of quantum mechanics, since this
would imply that nature makes use of both the detection
loophole in the Innsbruck experiment and of the
locality loophole in the NIST experiment. Nevertheless,
nature could be vicious, and such an experiment is desirable
if we are to finally close the book on local realism." Then they discuss GHZ and do not claim that a loophole-free experiment had been performed. This article is recent, unlike the 1998 article in arxiv that I quoted before, so it looks like I did not misrepresent Zeilinger's opinion.

 

[SpectraCat]

Instantaneous propagation is a contradiction in terms.

FTL propagation is not demonstrated.

ok ..

QM projection along transmission axis of polarizer transmitting detected disturbance is based on assumption of local common cause.
[/QUOTE]

Please explain this somewhat cryptic statement in more detail. Do you mean that the interpretation assumes that the photon has to interact locally with the polarizer in order for the measurement at a given detector to occur? Or do you mean something else?

There are only two values for angular difference of polarizers wrt which A and B are perfectly correlated (anticorrelated). These correlations at these settings have a local common cause explanation. There are no other A<->B correlations to explain.

Please elaborate on the "local common cause explanation" in this case, not in terms of the Aspect '82 experiment you have mentioned before, but rather in terms of a modern experiment where both polarization components are detected at each detector, so that in the ideal case (100% detector efficiency) there would be no missed detection events.

The coincidental detection angular dependency can be reproduced via LHV formulation.

No, it cannot. If you are referring to the discussion we have been having recently, as I stated in my last post, your "broken entanglement" source produces results that are fundamentally different from the predictions of QM, in that they never go to zero for *any* choice of theta. You have certainly agreed previously that for entangled particles, there will be a relative detector setting (0 or pi, depending on the entangled state), which produces a coincidence rate of zero.

What's the intuitive support for nonlocality?

Who needs it? Where's the intuitive support for the speed of light being a fundamental physical "speed limit"?

Imho, nonlocality only exists via the manipulation of terms and misinterpretation.

Yikes ... IMO, that O is not very H More to the point, I guess you don't dispute that SQM predicts some non-local phenomena? Are those predictions "manipulations of terms" or "misinterpretations" in your view, and why?

 

[yoda jedi]

In the entangled state polarization is undetermined and QM just specifies the relationship between the counter-propagating disturbances incident on the polarizers.

Afaik, when polarization is determined, then entanglement is broken. The polarization is determined by the polarizer via transmission along its axial setting.

on pre-determined (polarization values) polarizers ?

but what about ten particles (previous pre-entangled) up and the other ten, down, then make the ten particles up to spin down, and see how spin the other ten particles....
if change the spin, well that`s no-locality, but i wish to see that...

 

[yoda jedi]

Who needs it? Where's the intuitive support for the speed of light being a fundamental physical "speed limit"?

maybe not INTUITIVE.
the "need" is for no-paradoxical reality or a self contradictory posibility.

need-> necessary = of an inevitable nature, logically unavoidable.

 

[Dmitry67]

Locality does not save you from the closed timelike curves inside kerr black holes anyway. In curved spacetime, "local" locality does not save you from the global non-local effects :)

 

[yoda jedi]

Locality does not save you from the closed timelike curves inside kerr black holes anyway. In curved spacetime, "local" locality does not save you from the global non-local effects :)

yes i know, a possible time travel,
maybe the REALITY is poly-ordered or omni-ordered, can coexist (in principle or possibily) past, present and the future.


irrespective of locality, have to be seen if the CPC negates CTCs.