EPR Debate: Nature Agrees with Einstein

[Kane O'Donnell]

[NB: the beam intensity needs to be varied by a method such as the introduction of attenuating plates, so that (under wave theory) each individual pulse of light (treated under QM as a single "photon") is reduced in intensity]

Look, I know I've just jumped in on this thread, but don't you see that you're not testing QM and your theory under the same conditions if you use 'intensity' in the wrong sense of the word?

I don't know what your theory says, but in modern physics the intensity of a *source* is related to the *number* of photons being emitted. This doesn't change the ENERGY of each photon - just keep that in mind. This is part of the reason why 'intensity' is gradually being replaced by the word 'irradiance', see for example Hecht, Optics. It's about the energy being delivered by photons per second rather than the amplitude of some wave.

So, to reduce the intensity of a light source you reduce the number of photons emitted. To reduce the intensity of a classical electromagnetic wave you reduce the amplitude. These two approaches OVERLAP in the classical limit, but the latter is NOT valid at low light levels, especially at optical frequencies. Photoelectric effect experiments clearly show that this 'intensity proportional to photon density' idea is correct, as is the idea that photons carry quanta of energy that cannot be reduced just by turning down the light.

Any theory which does *not* define intensity in terms of energy being delivered per second by lumped energy carriers contradicts experiment. This, naturally, includes classical electromagnetism.


Kane

 

[JohnBarchak]

Good try, but there is no conflict between this and QM. If there is, where is the experiment?

I assume from your answer that the Principle of Local Action which
"characterises the relative independence of objects far apart in space (A and B): external influence on A has no direct influence on B"
is in agreement with QM and that QM is a local theory.

The experiments are being done minute by minute in chemistry, biology, physics and all the other sciences - the Principle of Local Action has never been violated.

All the best
John B.

 

[DrChinese]

I assume from your answer that the Principle of Local Action which
"characterises the relative independence of objects far apart in space (A and B): external influence on A has no direct influence on B"
is in agreement with QM and that QM is a local theory.

The experiments are being done minute by minute in chemistry, biology, physics and all the other sciences - the Principle of Local Action has never been violated.

All the best
John B.

QM is not a local realistic theory. What is the experiment that will distinguish QM from Einstein's Locality? I know of no such experiment. I realize you coyly say "experiments" done every day prove this locality but this is also true with QM.

It is totally false, anyway, to assume that non-locality has implications which negate everyday experience. We don't know. Perhaps there are space dimensions such that every point in the universe is nearby in that spatial dimension? The point is that the simplistic local realism contemplated by EPR is non-existent. How is that any weirder than special or general relativity? It is what it is.

 

[vanesch]

Any theory which does *not* define intensity in terms of energy being delivered per second by lumped energy carriers contradicts experiment. This, naturally, includes classical electromagnetism.

Hi Kane,

For your information: "local realists" know that they are in trouble once they accept the existence of photons, so they deny it, but this usually comes out very late in the discussion. Having some experience in discussing with them it is a useful question to be clear on that first.
The reasoning presented is usually that they have "local realist models" that explain in a natural way the Aspect like experiment (exploiting the efficiency loophole). In doing so, they usually use classical EM, and the fact that counters are square-law devices responding to classical intensity (say, the Poynting vector). This can indeed sound convincing, if you do not explicitly talk about photons. However, if you then ask them how they interpret OTHER experiments, like the anti-coincidence experiments, then they tell you that there is no problem in it, in that the photon is send left or right in a deterministic way in the beam splitter. When you then ask how you can get interference between the two split beams, you get as an answer that this is explained by classical EM. However, they fail to come up with a coherent scheme which can explain/predict all these experiments in one single vision, as does QM. But you can be busy for tens of posts before realizing that they in fact deny photons.

cheers,
Patrick.

 

[Kane O'Donnell]

Thanks very much Patrick. I'm not particularly familiar with EPR paradox and similar things, but I can't see how the existence of photons can be denied in any model which seeks to coherently explain all aspects of the interaction of light and matter. In particular, since classical EM can be *recovered* from quantum theory in the low-frequency, long wavelength limit, I don't see how any experiment that is 'explained' by classical EM cannot also be explained from the photon point of view.

I would guess that the only way that one could distinguish between classical EM and quantum theory in the experiments that have been discussed is to use extremely low intensity devices - is it then the problem that detector efficiency limits our ability to get results?

Kane

 

[vanesch]

I would guess that the only way that one could distinguish between classical EM and quantum theory in the experiments that have been discussed is to use extremely low intensity devices - is it then the problem that detector efficiency limits our ability to get results?

No, there are very clear experiments proving the existence of photons.
Have a look at the following experiment:

Am. J. Phys. Vol 72, No 9 (1210), September 2004 by Thorn et al.

What they do is the following:

They send an entangled photon pair (from a PDC xtal) in two optical fibres.
One photon goes to the "trigger" detector, to open the coincidence time window for the second one.
The second one goes onto a 50-50 beam splitter and each arm goes onto a photon detector (D1 and D2).
The trick is to show that during the coincidence window with the trigger, at most ONE D1 or D2 triggers, and that coincidences trigger-D1-D2 are extremely rare.
This cannot be explained by classical EM. Indeed, even assuming that out of the Xtal come two correlated intensity bunches, one triggering the photodetector "trigger", then the intensity of the second bunch is divided equally (beamsplitter) on D1 and D2. So, due to the finite efficiency of D1 and D2 of "clicking" on incoming classical intensity, you should find a statistical distribution between "no click", "D1 OR D2 click" and "D1 AND D2 click". THIS IS NOT OBSERVED. The (D1 AND D2) click ratio is strongly suppressed as compared to what one should expect by an "intensity response" of the photodectors, and the very low remaining coincidence is explained by the finite duration of the time window of coincidence (and hence the Poissonian probability of capturing 2 photon pairs).

You CAN explain this experiment classically if you somehow turn your 50-50 beamsplitter into a random "left-right" switch (but you should then explain how it comes that a beam splitter suddenly works that way!). But then you cannot explain why exactly that same beamsplitter, with exactly the same beam, can give interference patterns between the two arms (if you remove the photodetectors D1 and D2). Indeed, if all the intensity goes randomly left or right in the beam splitter (the only way to explain the anticoincidence), then every possible interference is excluded.

The nice thing about this paper is that you do not need to correct any data: the raw data of coincidence clicks are clean enough to prove the point.

cheers,
Patrick.

 

[Kane O'Donnell]

That's very impressive - I didn't know that there were experiments of that form that can be used as evidence for the quantum mechanical view of light. Still, there's no need to convince me, of course, I've seen enough laser theory to know that you'd have a hard time explaining stimulated emission without a photon viewpoint.

I'm afraid I don't have much to contribute to the LR discussion, but thanks for your information, Patrick.

Kane

 

[ZapperZ]

That's very impressive - I didn't know that there were experiments of that form that can be used as evidence for the quantum mechanical view of light. Still, there's no need to convince me, of course, I've seen enough laser theory to know that you'd have a hard time explaining stimulated emission without a photon viewpoint.

I'm afraid I don't have much to contribute to the LR discussion, but thanks for your information, Patrick.

Kane

Oh sure! I posted the info about this article on 09-07-2004 (on here and in my journal entry) and vanesch gets the credit for it! :) :)

Take note that experiements such as this are no longer "exotic". In fact, this particular paper was describing an experiment done for an undergraduate advanced lab!

Zz.

 

[DrChinese]

Oh sure! I posted the info about this article on 09-07-2004 (on here and in my journal entry) and vanesch gets the credit for it! :) :)

Take note that experiements such as this are no longer "exotic". In fact, this particular paper was describing an experiment done for an undergraduate advanced lab!

Zz.

Here is a direct link to the paper: http://marcus.whitman.edu/~beckmk/QM/grangier/Thorn_ajp.pdf . The authors make an extremely persuasive case.

Mark Beck (Whitman University) is one of the co-authors. He is working on a series of similar tests using PDCs, including tests of Bell Inequalities. As Vanesch states, these are for undergraduate courses specifically which I think is very exciting.

-------------

As to the arguments for local realism: there is no purpose whatsoever to attacking a useful theory like QM unless something better can be put forth in its place. This would be the case EVEN IF (however unlikely) QM was wrong in some particular... because it would still have the exact same utility regardless. As is true with Newtonian gravity after GR.

No one is asserting that we know everything there is to know about QM, or that as currently stated it is final. All we do say is: The EPR paradox - that the possibility of a more complete specification of the system was demonstrated - has been resolved. Result: it has not been demonstrated to be a consequence of QM. Perhaps in the future, someone WILL demonstrate a more complete specification of the system.

 

[ZapperZ]

Here is a direct link to the paper: http://marcus.whitman.edu/~beckmk/QM/grangier/Thorn_ajp.pdf . The authors make an extremely persuasive case.

Mark Beck (Whitman University) is one of the co-authors. He is working on a series of similar tests using PDCs, including tests of Bell Inequalities. As Vanesch states, these are for undergraduate courses specifically which I think is very exciting.

You may want to read a new paper that also described not just one, but a set of undergraduate experiments (5 to be exact) similar to the one here.[1] I have included a short description of it in the latest entry of my journal.

It is unfortunate that many people who freely and continuously come up with apparent "lack of evidence" for the existence of photons either do not understand, nor have ever perform experiments such as these. I am glad that such experiments, which would have been rather daunting to be performed at this level years ago, are becoming more common and accessible.

Zz.

[1] E. J. Galvez et al. Am. J. Phys. v.73, p.127 (2005).

 

[RandallB]

The only thing the beamsplitter test proves is that photons are particles not waves.
And I can see where Bell can “disprove” the classical view, IF the view is restricted to a classical EM or WAVE view.
But cannot there be a classical view of the “particle”. As in:
*An individual photon is polarized based by its spin, on an axis perpendicular to its travel with V H D etc. alignments.
* V photons always absorbed by H filter, always passed by a V filter.
* Diagonal filters destroy the old spin on a V or H photon allowing it to pass based the position of the field of ‘whatever’ is spinning and how (maybe like a baton in the hand of a majorette) when it interacts with the D filter. With passing being a function related to $$cos^2\theta$$.
*And if successful in passing, allowing the spin to continue only inline with the angle of the diagonal filter not the original V or H alignment. The greater the amount of spin realignment required the less likely the photon will pass through.
(This isn’t a QM view is it?)

Now I may be an amateur to even imagine such an explanation. But it seems more classical in context than QM. It would not require adherence to Bell Statistical math. And also resolves the “polarization paradox”. Maybe QM also explains the “polarization paradox” also, but so far I’ve not found that anywhere.

So if this could be a true part of a classical explanation of the particle. The EPR test won’t be capable of eliminating either view as both use $$cos^2\theta$$.
This only shows the need for a better test, it certainly does not confirm the LR view.

PS: “polarization paradox”
Light totally blocked by filters V H also V H D
But light goes through filters V D H

 

[DrChinese]

The only thing the beamsplitter test proves is that photons are particles not waves.
And I can see where Bell can “disprove” the classical view, IF the view is restricted to a classical EM or WAVE view.
But cannot there be a classical view of the “particle”.

No, Bell absolutely applies in this situation. Photons are still photons, which is what is measured in every experiment. Also, recall that the EPR and Bell papers themselves discussed spin 1/2 particles (electrons).

The LR crowd tried to escape the Bell results by claiming there was no evidence that photons were quantized. That never made any sense, but these experiments prove it conclusively. The "table top" experiment Vanesch mentions saw a violation of the classical (Maxwell) predictions by 100+ standard deviations, and very close agreement with QM.

Wave theory predicted: >=1.0000
QM predicted: .0000
Actual: .0118

 

[JohnBarchak]

Of Einstein, Podolsky, Rosen, Bohm and Bell

I have yet to encounter a proponent of quantum theory who has even a basic understanding of the EPR gedanken experiment - but I guess Bohr did give absolution to quantum people from having to understand anything. Most think that it has something to do with the Bohm/Bell proposed experiments involving spin or polarization. None appear to realize that the EPR gedanken experiment and the Bohm/Bell proposed experiments are fundamentally different. Actually, the EPR gedanken experiment involves the breakup of a molecule of two identical
atoms. The two resulting particles move in opposite directions at the same speed (classical conservation), so their positions and momenta are obviously correlated in continuous Einstein 4 space. Bell proved absolutely nothing as far as the original EPR gedanken experiment. For those who want to believe that Bell proved something, please call it the Bell gedanken experiment for photons or for Bohm's electron spin gedanken experiment, call it EPRB.

The main thing to remember is that Bohr's denial of the EPR "elements of reality" was essentially a denial of the scientific method and the principles of engineering. If the functional relationship between the two particles in the EPR gedanken experiment is not real, then almost nothing in science or the principles of engineering can be
considered real. We are left with mysticism and voodoo. It is incredible that rational people even consider the denial the EPR "elements of reality". I think that Einstein was in a state of shock until the day he died.

Of Einstein, Podolsky, Rosen, Bohm and Bell

In "Einstein, Podolsky and Rosen versus Bohm and Bell", Andrei Khrennikov and Igor Volovich explain how the EPR gedanken experiment and the Bohm/Bell proposed experiments are fundamentally different:

"In 1935 Einstein, Podolsky and Rosen (EPR) advanced an argument about incompleteness of quantum mechanics [1]. They proposed a gedanken experiment involving a system of two particles spatially separated but correlated in position and momentum and argued that two non-commuting variables (position and momentum of a particle) can have simultaneous physical reality. They concluded that the description of physical reality given by quantum mechanics, which does not permit such a simultaneous reality, is incomplete.

Though the EPR work dealt with continuous variables most of the further activity have concentrated almost exclusively on systems of discrete spin variables following to the Bohm [2] and Bell [3] works.

Bell's theorem [3] states that there are quantum spin correlation functions that can not be represented as classical correlation functions of separated random variables. It has been interpreted as incompatibility of the requirement of locality with the statistical predictions of quantum mechanics [3]. For a recent discussion of Bell's theorem see, for example [4] - [17] and references therein. It is now widely accepted, as a result of Bell's theorem and related experiments, that "Einstein`s local realism" must be rejected. For a discussion of the role of locality in the three dimensional space see, however, [16, 17].

The original EPR system involving continuous variables has been considered by Bell in [18]. He has mentioned that if one admits "measurement" of arbitrary "observables" on arbitrary states then it is easy to mimic his work on spin variables (just take a two-dimensional subspace and define an analogue of spin operators). The
problem which he was discussing in [18] is narrower problem, restricted to measurement of positions only, on two non-interacting spinless particles in free space. Bell used the Wigner distribution approach to quantum mechanics. The original EPR state has a nonnegative Wigner distribution. Bell argues that it gives a local,
classical model of hidden variables and therefore the EPR state should not violate local realism. He then considers a state with nonpositive Wigner distribution and demonstrates that this state violates local realism.

Bell's proof of violation of local realism in phase space has been criticized in [19] because of the use of an unnormalizable Wigner distribution. Then in [20] it was demonstrated that the Wigner function of the EPR state, though positive definite, provides an evidence of the nonlocal character of this state if one measures a
displaced parity operator.

In this note we apply to the original EPR problem the method which was used by Bell in his well known paper [3]. He has shown that the correlation function of two spins cannot be represented by classical correlations of separated bounded random variables. This Bell's theorem has been interpreted as incompatibility of local realism with quantum mechanics. We shall show that, in contrast to Bell's theorem for spin correlation functions, the correlation function of positions (or momenta) of two particles always admits a representation in the form of classical correlation of separated random variables. This result looks rather surprising since one thinks that the Bohm-Bell reformulation of the EPR paradox is equivalent to the original one."

The entire paper may be found at:
http://arxiv.org/PS_cache/quant-ph/pdf/0211/0211078.pdf

References
[1] A. Einstein, B. Podolsky, and N. Rosen, Phys. Rev. 47(1935)777.
[2] D. Bohm, Quantum Theory, Prentice-Hall, Englewood Cliffs, 1951.
[3] J.S. Bell, Physics, 1, 195 (1964).
[4] J.F. Clauser, A. Shimony, Report. Progr. Physics, 41(1978)1881.
[5] J.F.Clauser, M.A. Horne, A. Shimony, and R.A. Holt,
Phys.Rev.Lett. 23,880 (1969)
[6] G. Weihs, T. Jennewein, C. Simon, H. Weinfurter, A. Zeilinger ,
Phys.Rev.Lett. 81
(1998) 5039-5043.
[7] S.L. Braunstein, A.Mann, and M. Revzen, Phys. Rev. Lett, 68, 3259
(1992)
[8] D. Collins, N. Gisin, N. Linden, S. Massar, S. Popescu, Phys.
Rev. Lett. 88, 040404
(2002).
[9] M. D. Reid, Phys. Rev. Lett, 84, 2765 (2000)
[10] A. Beige, W. J. Munro, P. L. Knight, Phys. Rev. A 62, 052102
(2000)
[11] Z.-B. Chen, J.-W. Pan, G. Hou, and Y.-D. Zhang, Phys. Rev. Lett.
88, 040406 (2002)
[12] A. Kuzmich, I.A. Walmsley, and L. Mandel, Phys. Rev. Lett, 85,
1349 (2000)
[13] H. Jeong, W. Son, M. S. Kim, D. Ahn, C. Brukner, quant-
ph/0210110.
[14] A. Yu. Khrennikov, Foundations of Physics, 32, 1159-1174 (2002).
[15] A.Yu. Khrennikov, Il Nuovo Cimento, B 115, N.2, 179-184, (1999).
[16] I. V. Volovich, in : Foundations of Probability and Physics, Ed.
A. Khrennikov, World Sci. 2001, pp.364-372.
[17] I. V. Volovich, quant-ph/0203030.
[18] J.S. Bell, Speakable and unspeakable in quantum mechanics,
Cambridge University
Press, Cambridge, 1987, p.196.
[19] L.M. Johansen, Phys. Lett. A236(1997)173
[20] K. Banaszek, K. Wodkiewicz , Phys. Rev. A 58, 4345 (1998)

 

[DrChinese]

I have yet to encounter a proponent of quantum theory who has even a basic understanding of the EPR gedanken experiment - but I guess Bohr did give absolution to quantum people from having to understand anything. Most think that it has something to do with the Bohm/Bell proposed experiments involving spin or polarization. None appear to realize that the EPR gedanken experiment and the Bohm/Bell proposed experiments are fundamentally different. Actually, the EPR gedanken experiment involves the breakup of a molecule of two identical
atoms. The two resulting particles move in opposite directions at the same speed (classical conservation), so their positions and momenta are obviously correlated in continuous Einstein 4 space. Bell proved absolutely nothing as far as the original EPR gedanken experiment. For those who want to believe that Bell proved something, please call it the Bell gedanken experiment for photons or for Bohm's electron spin gedanken experiment, call it EPRB.

The main thing to remember is that Bohr's denial of the EPR "elements of reality" was essentially a denial of the scientific method and the principles of engineering. If the functional relationship between the two particles in the EPR gedanken experiment is not real, then almost nothing in science or the principles of engineering can be
considered real. We are left with mysticism and voodoo. It is incredible that rational people even consider the denial the EPR "elements of reality". I think that Einstein was in a state of shock until the day he died.

etc. etc.

John,

You adeptness at quoting long tracts of others' work with no value added is acknowledged.

1) You continue to ignore the challenge I have laid out for you: Describe a specific experiment that separates the men from the boys. You say that your position is so incredibly amazing that the rest of us are too dumb to comprehend (I apparently lack "basic understanding"); well, perhaps that door swings both ways. I am not impressed by claims of brilliance. Actual brilliance impresses me. Where is yours? Show us a specific experiment, we've heard enough big claims from you already.

2) You state that "most" think EPR had to do with "spin or polarization". I think instead that most folks here know the following: EPR thought they had demonstrated that QM was not complete because a more complete specification of the system was possible. I don't think it ever occurred to EPR that something like the Bell Theorem would come along. Clearly, if the entangled particles have specific definite attributes as EPR envisioned them, then a more complete specification IS possible (in principle). You are free to ignore Bell and say it does not disprove EPR. But you are splitting hairs while everyone else has passed you by and left you in the dust. Bell says that the hypothesis that a more complete specification of the system is possible (in the manner of the EPR paradox) is falsifiable via experiment. Experiment performed, hypothesis rejected.

 

[JohnBarchak]

Please clarify for me - does QM satisfy Einstein's Principle of Local Action or does it not? You can't sit on the fence forever.

All the best
John B.

 

[DrChinese]

Please clarify for me - does QM satisfy Einstein's Principle of Local Action or does it not? You can't sit on the fence forever.

All the best
John B.

a) In my personal opinion, it does. I tend to believe in local non-reality. A light cone limits propagation of causes towards effects. Particles do not have precise definite real attributes outside of the context of a measurement.

b) Others think that reality is non-local. (A reasonable position, too, IMHO.) In that case, there are instances in which what appears non-local from one space-time perspective is local from another. In that case, the other side of the universe is close if you could approach from the correct dimension.

In either case, the QM formalism is sufficient to be useful.

Now, when are you going to address my challenge? An experiment to separate your use of hyperbole into something of substance?

 

[JohnBarchak]

Dehmelt's Penning trap capture of an electron, which in Dehmelt's words was "drastically at odds with the famous Physicist Heisenberg's claim that an electron truly at rest could not be localized and could be found anywhere in space." This totally blows away QM.

The Aspect experiment is used as proof of the non-local character of physics. If the Principle of Local Action were to be completely abolished, the Bell Test experiments would have no validity since the test apparatus could be influenced (in unknown ways) by events at the other side of the universe. Since a counter example experiment to the Principle of Local Action has never been found, this totally blows away QM. Remember that for superposition to work, spooky action at a distance MUST occur. Actually, it never occurs.

I've got many more examples if you want to hear about them.

 

[DrChinese]

Dehmelt's Penning trap capture of an electron, which in Dehmelt's words was "drastically at odds with the famous Physicist Heisenberg's claim that an electron truly at rest could not be localized and could be found anywhere in space." This totally blows away QM.

The Aspect experiment is used as proof of the non-local character of physics. If the Principle of Local Action were to be completely abolished, the Bell Test experiments would have no validity since the test apparatus could be influenced (in unknown ways) by events at the other side of the universe. Since a counter example experiment to the Principle of Local Action has never been found, this totally blows away QM. Remember that for superposition to work, spooky action at a distance MUST occur. Actually, it never occurs.

I've got many more examples if you want to hear about them.

Your logic blows me away. Where is the beef, John? You talk the talk, but...

A quote by Dehmelt is not experimental evidence of anything - you fail to address the most basic of challenges. Give an experiment that falsifies QM. Or give a description of an actual experiment that separates your view from QM. (Oh, and make sure your theory gives identical predictions in all other places.)

Unless you are God, I do not see how any of us have the power to enforce OR abolish the "Principle of Local Action". No one, least of all myself, has said that a cause can be made to propagate outside a light cone. So what is your point?

Spooky action at a distance is one *possible* consequence of Aspect. Aspect happened. Do you simply refuse to accept experimental results you do not care for? If so, save us a lot of time right now and tell us what you believe instead of hiding behind a curtain.

 

[vanesch]

The only thing the beamsplitter test proves is that photons are particles not waves.

I would drop the "not waves", but indeed, it means that there is some entity that "doesn't split". So you "detect a photon or you don't detect it", and you do not detect 3/4 of a photon.

Once this is accepted, you can say that a photodetector clicks when it sees a photon, with a certain efficiency, and that that efficiency can slightly depend on the energy of the photon (easily checked: it is the quantum efficiency as a function of frequency), it can eventually depend on the polarization (easily checked, usually this is flat) and of course it depends in a trivial way on position: you hit the photocathode or you miss it :-) But if you are not too clumsy an experimentalist, you restrict the impact zone to the middle portion of the photocathode, where you are independent of position.
And there is nothing else the efficiency can depend upon.

And I can see where Bell can “disprove” the classical view, IF the view is restricted to a classical EM or WAVE view.
But cannot there be a classical view of the “particle”. As in:
*An individual photon is polarized based by its spin, on an axis perpendicular to its travel with V H D etc. alignments.
* V photons always absorbed by H filter, always passed by a V filter.
* Diagonal filters destroy the old spin on a V or H photon allowing it to pass based the position of the field of ‘whatever’ is spinning and how (maybe like a baton in the hand of a majorette) when it interacts with the D filter. With passing being a function related to $$cos^2\theta$$.
*And if successful in passing, allowing the spin to continue only inline with the angle of the diagonal filter not the original V or H alignment. The greater the amount of spin realignment required the less likely the photon will pass through.

But is it EXACTLY to such a situation that Bell applies, and this is exactly quantum mechanics ! Indeed, the photons that pass have the polarization of the last filter.
Now, the correlations mentioned in Bell correspond to the correlations of clicks when we choose two different angles for the polarizers in the two beams.
For instance, we know that the polarizations are "opposite" in the two photons of a photon pair. So if one polarizer is horizontal, and let's pass, and the other one is vertical, it should let pass. "100% correlation" but of course not in practice because of the finite efficiencies.
If one polarizer is horizontal, and the other one under 45 degrees, there is no correlation (50%), in that, if you know the first photon passed horizontal, the other one is vertical and upon a 45 degree polarizer it has 50% chance of passing (and yes, it will then come out as a 45 degree photon, but we don't care about that).
If you accept an independent finite efficiency for detecting a photon, as explained above, then you can extract the ideal correlations from the measurements ; for instance, if the efficiency of the detectors are, say, 34%, and in the case of X - Y you expect 100% ideal correlation, you should find 34% correlation in your data (because each time the photon got through, it had a chance of 34 % of clicking).
When you do that for different angles, you find a clear violation of the Bell inequalities. These are the Aspect like experiments.

There is no reasonable way in which these efficiencies should suddenly be a function of polarization (while you can check that, by using a polarized beam and looking at the average click rate when you turn it). But LR proponents say that it is STILL possible that in this kinds of experiments the efficiencies change exactly in the way to make us think that if they weren't we had a violation of Bell's inequalities. And indeed, theoretically such a possibility must be considered for a "loophole free" test. So this is the famous "efficiency loophole".

cheers,
Patrick.

 

[JohnBarchak]

With 10% efficiency on photon detection, the total inability to determine how many photons are involved, and the total inability to determine the energy involved, it is absolutely amazing that anyone concluded anything. I do not blame Aspect; he was not the one making the incredible claims.

All the best
John B.

 

[DrChinese]

And indeed, theoretically such a possibility must be considered for a "loophole free" test. So this is the famous "efficiency loophole".

cheers,
Patrick.

Vanesch,

I freely acknowledge the "detection loophole" and the "fair sampling" assumption (see more on that, next post, reference probably stolen from you already anyway). The question, don't you think, is what is its significance?

We could also have a leap year loophole. Scientific experiments run in a leap year give different results than other years. Or if run in the Southern hemisphere. Or in *France*, for god's sake. The point is, why is it that only EPR tests should have such loopholes heaped upon them? Why not double slit experiments, etc. etc.

This same thing - creating ad hoc evidentiary requirements - is also done to evolutionary theory. (Next we will be hearing about "intelligent design" in EPR experiments.) I guess, to be fair, special relativity (and the "one way speed of light" controversy) gets some of the same heaped upon it.

It seems to me that improvements in technology (and therefore leading to experiments with greater accuracy) render such "loopholes" as rapidly approaching moot status. I guess the great thing about science is that nothing is ever quite 100.0000% settled.

 

[DrChinese]

With 10% efficiency on photon detection, the total inability to determine how many photons are involved, and the total inability to determine the energy involved, it is absolutely amazing that anyone concluded anything. I do not blame Aspect; he was not the one making the incredible claims.

All the best
John B.

You are way behind:

Experimental violation of a Bell's Inequality with efficient detection
M. A. Rowe, et al
Nature, vol 409, February 2001

CHSH value of 2.25+/-.03 where 2.00 is the max allowed by local realistic theories. "...the high detection efficiency of our apparatus eliminates the so-called detection loophole. ... The result above was obtained using the outcomes of every experiment, so that no fair sampling hypothesis was required."

By the way, there is nothing weird about drawing strong conclusions from small samples. There is a branch of science called "statistics" ... you might learn from its study!

 

[vanesch]

We could also have a leap year loophole. Scientific experiments run in a leap year give different results than other years. Or if run in the Southern hemisphere. Or in *France*, for god's sake. The point is, why is it that only EPR tests should have such loopholes heaped upon them? Why not double slit experiments, etc. etc.

This same thing - creating ad hoc evidentiary requirements - is also done to evolutionary theory. (Next we will be hearing about "intelligent design" in EPR experiments.) I guess, to be fair, special relativity (and the "one way speed of light" controversy) gets some of the same heaped upon it.

Exactly. That's why I stopped discussing with these people ; we have two fundamentally different ways of viewing of how science works. Science works (in my opinion, which is, I think, well-informed on the question) on two requirements:
1) logical consistency and sufficient generality of a theory (which is essentially a way of mapping "things in the lab" onto a mathematical model, within boundaries, but not tied to specific lab situations ad hoc)
2) agreement between numerical predictions by said theory in given circumstances describing and experiment and the actual outcomes of those experiment.

The logical consequence is that you can disprove specific theories (either because they don't satisfy 1) or because they fail on 2)), or even specific classes of theories which is just a loop over 1) and 2). But you can never PROVE a theory, nor can you disprove one particular aspect of what could be contained in 1).

And it is exactly that what many people try to do, or accuse "scientists" to fail to do. No, you cannot *absolutely prove* QM, or the *existence of photons*. You can only show that theories using this make accurate predictions and satisfy up to date 1) and 2), and compare this to other theories which satisfy also 1) (such as classical optics). You cannot prove the inexistence of LR theories if the class is too wide.

What they should do, in order to be taken seriously, is to produce specific theories, or classes of theories, that contain their pet principle, and satisfy 1) and 2). But they rarely (if ever) do.

They just say: hey, for _this_ specific experimental result, I can think up a theory that respects my pet principle and produces the same results - if I'm allowed to change the behaviour of all known apparatus. But for the next experiment, they do the same, but with DIFFERENT theories and different behaviour of the apparatus. This means that their view doesn't satisfy 1).

The nicest attempts that I've seen were "stochastic Electrodynamics". I think it has a problem with thermodynamics, and with the rest of quantum theory, but at least it tried to construct an equivalent theory in optics having LR.

cheers,
Patrick.

 

[JohnBarchak]

You are way behind:

Experimental violation of a Bell's Inequality with efficient detection
M. A. Rowe, et al
Nature, vol 409, February 2001"

YOU are the one who brought up Aspect!

 

[RandallB]

MY "Classical view" of the photon as a particle

But is it EXACTLY to such a situation that Bell applies, and this is exactly quantum mechanics ! Indeed, the photons that pass have the polarization of the last filter. .

So if my "Classical view of a particle" is QM, can you help me understand the mechanics of how QM explains a photon changes its polarization as it goes through a filter?

ALSO

For instance, we know that the polarizations are "opposite" in the two photons of a photon pair. So if one polarizer is horizontal, and let's pass, and the other one is vertical, it should let pass. "100% correlation"
Patrick.

Just to confirm a point (maybe only important to the testers) but somewhere I'd picked up the idea that entangled photons came out with the same polarization. Testers must set there 0 degeres mark for correlation in test areas A and B 90 degrees apart from each other, correct?

Thanks, I think I'm getting it.

 

[DrChinese]

1. MY "Classical view" of the photon as a particle
So if my "Classical view of a particle" is QM, can you help me understand the mechanics of how QM explains a photon changes its polarization as it goes through a filter?

2. ALSOJust to confirm a point (maybe only important to the testers) but somewhere I'd picked up the idea that entangled photons came out with the same polarization. Testers must set there 0 degeres mark for correlation in test areas A and B 90 degrees apart from each other, correct?

Thanks, I think I'm getting it.

1. Vanesch can probably answer this better. As far as I know, there is no real "mechanical" explanation of spin intrinsics. It just is. This is one of the elements of QM that some find objectionable. By analogy, it is no different than what happens when an electron moves from one orbital to another. It just does.

2. I always refer to 0 degrees as the correlated case because it is easier to discuss. Actually the spins are crossed - i.e. 90 degrees apart - but that is easily compensated for as you state.

 

[DrChinese]

YOU are the one who brought up Aspect!

?

OK, here is another simple question for you to evade: do you or do you not accept the results of Aspect as proof of a violation of Bell's Inequality?

If the answer is NO, then: do you or do you not accept the results of Rowe as proof of a violation of Bell's Inequality?

 

[vanesch]

MY "Classical view" of the photon as a particle
So if my "Classical view of a particle" is QM, can you help me understand the mechanics of how QM explains a photon changes its polarization as it goes through a filter?

Because in quantum mechanics, an x-polarized photon can just as well be seen as a superposition of a 45 degree left, and a 45 degree right polarized photon. And then only one of the two components gets true. It is not that there is a mechanistic explanation of something "tilting" the axis of polarization. In QM formalism, it is just a "change of basis". But you touch indeed upon one of the most bizarre properties of QM. In fact, all these things are different expressions of THE bizarre property of QM, namely the superposition principle. And it is the cornerstone of QM which gives rise to about all of its results.
However, in this particular case, the analogy with classical optics is striking: you wouldn't argue that something "tilted" the plane of the E-field when it went through a polarizer, right ? Well, exactly the same thing applies to the photon.

ALSOJust to confirm a point (maybe only important to the testers) but somewhere I'd picked up the idea that entangled photons came out with the same polarization. Testers must set there 0 degeres mark for correlation in test areas A and B 90 degrees apart from each other, correct?

In fact, both occur. Some parametric down converters are of type I, and then indeed, both have the same polarization. Others are of type II, and then they are perpendicularly polarized. (or was it the opposite?).

cheers,
Patrick.

 

[Cat]

... do you or do you not accept the results of Rowe as proof of a violation of Bell's Inequality?

I think it is in http://arxiv.org/abs/quant-ph/0102139 that Lev Vaidman explains why, though an inequality was violated, we don't have to interpret it as illustrating entanglement: the ions in Rowe's experiment were very close together. The measurements on them could not be considered (as required for the Bell inequality) to be independent.

Cat

 

[DrChinese]

I think it is in http://arxiv.org/abs/quant-ph/0102139 that Lev Vaidman explains why, though an inequality was violated, we don't have to interpret it as illustrating entanglement: the ions in Rowe's experiment were very close together. The measurements on them could not be considered (as required for the Bell inequality) to be independent.

Cat

Lev doesn't think that experiment has eliminated the detection ("fair sampling") issue because of the locality issue. But that is merely one person's opinion.

It is clear to me from the Rowe and Aspect experiments (and others such as Weihs):

a. Locality: the Inequality is violated whether or not the apparatus is space-like separated, per Weihs. (Requiring this never made any sense in the first place, because it requires the existence of physical effects never otherwise witnessed.)

b. Fair Sampling: the Inequality is violated whether or not a fair sample is obtained, per Rowe. (Requiring a complete sample never made sense to me either, as a large subsample should not possibly show more correlations than are actually present in the full population.)

Combining these two, you know that locality and sampling are not factors in the correlated events. That should be sufficient to address the lingering doubts of most scientists.

 

[ZapperZ]

I think it is in http://arxiv.org/abs/quant-ph/0102139 that Lev Vaidman explains why, though an inequality was violated, we don't have to interpret it as illustrating entanglement: the ions in Rowe's experiment were very close together. The measurements on them could not be considered (as required for the Bell inequality) to be independent.

Cat

While this may not be entirely relevant to the point you're trying to make, take note that the existence of entanglement is not solely verified via the EPR-type experiments. 2 entangled photons, for example, are not separable and can essentially be described as a connected, single system. It means that it is a macro particle with twice the energy of a single, isolated photon. If this is true, then one should be able to do a diffraction experiment with a higher resolution using the entangled pair than with single photon since the entangled macro particle has twice the energy (and thus, half the wavelength) of a single, unentangled photon.

Guess what? That's what has been observed, and in two separate experiments![1,2] The entangled photons can beat the diffraction limits of single photons. The first experiment showed interference patterns from a state of 3 entangled photons, while the other showed a state of 4 entangled photons. In both cases, the resolution was better than for a single photon: they were lambda/3 and lambda/4 respectively, as expected.

One can read a brief report of these experiements here

http://physicsweb.org/article/news/8/5/6

As is typical in physics, a particular idea, principle, or theory, isn't verified with just one experiment. Often, several difference experiments and techniques are required for a convincing verification. This appears to be the case here.

Zz.

[1] P. Walther et al., Nature v.429, p.158 (2004).
[2] M.W. Mitchell et al., Nature v.429, p.161 (2004).

 

[marlon]

One can read a brief report of these experiements here

http://physicsweb.org/article/news/8/5/6

As is typical in physics, a particular idea, principle, or theory, isn't verified with just one experiment. Often, several difference experiments and techniques are required for a convincing verification. This appears to be the case here.

Zz.

[1] P. Walther et al., Nature v.429, p.158 (2004).
[2] M.W. Mitchell et al., Nature v.429, p.161 (2004).

Hi ZapperZ,

this article is very interesting. I do have a question though because this experiment is not entirely clear to me. Let me explain how i see it : if two photons are entangeled their wavelength is indeed half the size of one photon. These photons can be entangeled via parametric down conversion. In order to check whether photons are entangeled can you do this ? : Suppose you construct a plate through which the photons have to pass. Make little holes in this plate so that photons can pass through them. Now (according to me, but i am not sure) the clue is to make the dimension of these holes as big as the wavelength of an entangeled pair so that "ordinary" unentangeled photons cannot pass through (their wavelength is too big)

Hence, the photons you detect after passing through the plate are entagneled for sure.

Is this the way to look at this experiment and does my point make sense?

Please elaborate if i am wrong...

Thanks in advance.

regards
marlon

 

[Cat]

Lev doesn't think that experiment has eliminated the detection ("fair sampling") issue because of the locality issue. But that is merely one person's opinion.

Surely one experiment with perfect detectors has no effect on the logic of a loophole that is present when they are not perfect? [See the original paper on the subject of the detection loophole -- Pearle, P, “Hidden-Variable Example Based upon Data Rejection”, Physical Review D, 2, 1418-25 (1970)]

It is clear to me from the Rowe and Aspect experiments (and others such as Weihs):

a. Locality: the Inequality is violated whether or not the apparatus is space-like separated, per Weihs. (Requiring this never made any sense in the first place, because it requires the existence of physical effects never otherwise witnessed.)

I agree that, in general, the separation is irrelevant. However see below for more on the Rowe et al experiment.

b. Fair Sampling: the Inequality is violated whether or not a fair sample is obtained, per Rowe. (Requiring a complete sample never made sense to me either, as a large subsample should not possibly show more correlations than are actually present in the full population.)

No, this has not been proven and the logic of Pearle's paper says it is not in general true. I've had a look at one of the papers on Rowe's experiment, and it is open to more problems than have so far been discussed. It is not only a straightforward matter of whether or not signals could have been exchanged (the locality loophole) and whether or not the sample was fair (the detection loophole). We agree, it seems, that the first is open but irrelevant, the second closed (since the sample was almost the entire population).

The problem here seems to be that Bell's inequality depends on being able to set your detectors independently and also on being able to measure your particles separately. It is not at all clear that the detector settings can be regarded as independent, and it is most certainly not true that the particles are measured separately. What is measured is the intensity of the combined signal from both. There is no way, when this is at half strength, of knowing which particle contibuted that half -- See Kielpinski, David et al, “Recent Results in Trapped-Ion Quantum Computing”, http://arxiv.org/abs/quant-ph/0102086.

Cat

 

[marlon]

Anybody here whot can help me out with the question in my previous post on detecting entangeled photons ?

Thanks
marlon

 

[ZapperZ]

Hi ZapperZ,

this article is very interesting. I do have a question though because this experiment is not entirely clear to me. Let me explain how i see it : if two photons are entangeled their wavelength is indeed half the size of one photon. These photons can be entangeled via parametric down conversion. In order to check whether photons are entangeled can you do this ? : Suppose you construct a plate through which the photons have to pass. Make little holes in this plate so that photons can pass through them. Now (according to me, but i am not sure) the clue is to make the dimension of these holes as big as the wavelength of an entangeled pair so that "ordinary" unentangeled photons cannot pass through (their wavelength is too big)

Hence, the photons you detect after passing through the plate are entagneled for sure.

Is this the way to look at this experiment and does my point make sense?

Please elaborate if i am wrong...

Thanks in advance.

regards
marlon

Keep in mind that to get any effects from diffraction, you need a opening that is of the order of, or less than the size of the wavelength. If the opening is considerably larger than the wavelength, you get no diffraction effects.

What you get in this case is that to get a diffraction pattern with the 2-photon case, the opening must be smaller than what you get with the 1-photon case. This is because the wavelength of the 2-photon macro particle is smaller than the single photon. So this is in the opposite direction of what you are describing.

Zz.