Loophole-free demonstration of nonlocality?

[bohm2]

Is anyone familiar with Suarez's papers in this area? I've posted his most recent and pertinent papers on the topic below and even though I read them all, I'm still having trouble understanding his arguments:

Further considerations on the similarities and differences between the kind of nonlocality demonstrated by our experiment and the better known form of nonlocality revealed by the violation of Bells inequality will be presented by some of us in a forthcoming publication.

Single-photon space-like antibunching
http://lanl.arxiv.org/pdf/1204.1712.pdf

The "forthcoming publications" include the following:

I discuss an experiment demonstrating nonlocality and conservation of energy under the assumption that the decision of the outcome happens at detection. The experiment does not require Bell's inequalities and is loophole-free...If one assumes that the decision of the outcome happens at detection, the experiment presented above is a clear demonstration of nonlocality (likely the first loophole-free one), and shows that this principle rules the whole quantum physics...If one rejects the view that the outcome is decided at detection, then one has to accept de Broglie's "empty wave" and at the end "many worlds", where the experimental violation of Bell's inequality even without detection loophole does not prove nonlocality.

"Empty waves", "many worlds", "parallel lives" and nonlocal decision at detection
http://lanl.arxiv.org/pdf/1204.1732.pdf

Interestingly, the PBR theorem is also mentioned in his most recent paper:

This interpretation is proved to be at odds with quantum mechanics by the recently established PBR theorem [11]. The formulation of this theorem according to [10, 12] shows that it rules out models that are "less random than quantum" but not models "less nonlocal than quantum". Conversely, the falsification of models "less nonlocal than quantum" [9] does not falsify "models less random than quantum".

Decision at the beam-splitter, or decision at detection, that is the question
http://lanl.arxiv.org/pdf/1204.5848.pdf

 

[DrChinese]

Very interesting stuff. Shows how these theorems - Bell, PBR, and now Suarez' - are allowing us to home in on things.

As I see the conclusion of these, the MWI picture is being attacked (although I may have misunderstood that point). He is asserting non-locality, although as I see it the time symmetric interpretations are not affected. Some people call these non-local although I don't usually group them that way. I call the results consistent with quantum non-locality, and the results are certainly what I would have expected. In fact...

I was surprised to see how closely the "Single-photon space-like antibunching" experiment was to earlier experiments, here is one example:

http://people.whitman.edu/~beckmk/QM/grangier/Thorn_ajp.pdf
Observing the quantum behavior of light in an undergraduate laboratory (2003)

They already knew that the 25% prediction of a local theory for double detections did not occur, and would be strictly against the quantum picture. This setup used the heralded photon and the beamsplitter as in the newer one, but did not enforce strict spacelike separation. The extension in the newer experiment was the transition from strict timelike to strict spacelike separation, which clarified those differences with the local picture.

 

[San K]

Interestingly, the PBR theorem is also mentioned in his most recent paper:
Decision at the beam-splitter, or decision at detection, that is the question
http://lanl.arxiv.org/pdf/1204.5848.pdf

From the article/reference above:

Can quantum mechanics be improved?|Does
the previous conclusions mean that quantum mechanics
is the ultimate theory and will not experience any further
improvement in the future? Not by any means. Quan-
tum physics has still to solve for instance the so called
\measurement problem" (Schrodinger cat paradox).

I thought the Schrodinger cat paradox (like the Twin paradox in relativity) was resolved before/at the time the paradox was created.

Both the paradoxes, I thought, we created to illustrate how they could be resolved within the frame work of QM (for Schrodinger cat paradox) or Relativity (for Twin paradox).

The Schrodinger cat paradox is resolved by the fact that the entanglement (superposition of states) is broken at some point/event after emission from the radioactive decay. We may not know exactly what that point/event is however there is no paradox. or alternatively we can say they were never paradoxes, (its a matter of semantics) since they were resolved at the time of creation (or little before).

Side note: all the paradoxes of relativity were resolved at the time of creation

 

[StevieTNZ]

From the article/reference above:



I thought the Schrodinger cat paradox (like the Twin paradox in relativity) was resolved before/at the time the paradox was created.

Both the paradoxes, I thought, we created to illustrate how they could be resolved within the frame work of QM (for Schrodinger cat paradox) or Relativity (for Twin paradox).

The Schrodinger cat paradox is resolved by the fact that the entanglement (superposition of states) is broken at some point/event after emission from the radioactive decay. We may not know exactly what that point/event is however there is no paradox.


or alternatively we can say they were never paradoxes, (its a matter of semantics) since they were resolved at the time of creation (or little before).

Side note: all the paradoxes of relativity were resolved at the time of creation

I don't think the cat paradox has been resolved at all.

 

[San K]

I don't think the cat paradox has been resolved at all.

I think that Schrodinger himself knew there was no cat paradox and he brought/made this up just to illustrate (or better understand) entanglement and to go further...for the same reason the twin paradox was bought up to illustrate (or better understand) relativity and to show that relativity still works and the twin paradox is resolvable within the framework of relativity.

Schrodinger was, I think, simply trying to bring out the idea that : it is hard to pin down when the entanglement breaks down.

None of them is a "true" paradox (its a matter of semantics though).

I am not aware of any "true/real/unsolved" paradox in physics/science, however I am not a physicist/scientist, so maybe true/unresolved paradoxes exist that I am not aware of.

 

[martinbn]

I think that Schrodinger himself knew there was no cat paradox and he brought/made this up just to illustrate (or better understand) entanglement and to go further...

What entanglement in the Schrodinger's cat "paradox"?

 

[San K]

What entanglement in the Schrodinger's cat "paradox"?

the entanglement between the atoms that are emitted from the decaying radioactive substance in the chamber with the cat.

Martinbn -- what is your point? what is your hypothesis? the conversation can be faster if you were to disclose that.

 

[martinbn]

the entanglement between the atoms that are emitted from the decaying radioactive substance in the chamber with the cat.

Martinbn -- what is your point? what is your hypothesis? the conversation can be faster if you were to disclose that.

My point is that the point of Schrodinger was not to illustrate (or better understand) entanglement, but to show that extrapolating quantum mechanical conclusions to the macro world leads to absurdity.

 

[DrChinese]

Suarez is asking: at what point is the superposition of states decided? Is it done at the point in the apparatus where the beamsplitter appears? Or is it done later, when the final configuation is known and the particle is detected?

A local realistic approach says that it must be decided at the beamsplitter, and that leads to a contradiction with his experiment (because sometimes a single photon should lead to 2 clicks, sometimes 0, but QM always predicts 1).

Where I get a bit confused is how the jump is made to non-locality. He uses a chain of logic to get this, but it seems to me that non-realistic interpretations are not ruled out.

 

[San K]

Suarez is asking: at what point is the superposition of states decided? Is it done at the point in the apparatus where the beamsplitter appears? Or is it done later, when the final configuation is known and the particle is detected?

A local realistic approach says that it must be decided at the beamsplitter, and that leads to a contradiction with his experiment (because sometimes a single photon should lead to 2 clicks, sometimes 0, but QM always predicts 1).

well summarized Dr Chinese

Where I get a bit confused is how the jump is made to non-locality. He uses a chain of logic to get this, but it seems to me that non-realistic interpretations are not ruled out.

I have not gone over it yet, maybe someone else in the forum might have.

 

[zonde]

Suarez is asking: at what point is the superposition of states decided? Is it done at the point in the apparatus where the beamsplitter appears? Or is it done later, when the final configuation is known and the particle is detected?

A local realistic approach says that it must be decided at the beamsplitter, and that leads to a contradiction with his experiment (because sometimes a single photon should lead to 2 clicks, sometimes 0, but QM always predicts 1).

Where I get a bit confused is how the jump is made to non-locality. He uses a chain of logic to get this, but it seems to me that non-realistic interpretations are not ruled out.

As I understood Suarez is assuming that decision is made at the event of detection. Because there are two spatially separate detectors measurement process is non-local (given results of experiment).
But if you assume decision is made at beamsplitter his reasoning does not apply.

 

[bohm2]

Suarez is asking: at what point is the superposition of states decided? Is it done at the point in the apparatus where the beamsplitter appears? Or is it done later, when the final configuation is known and the particle is detected? A local realistic approach says that it must be decided at the beamsplitter, and that leads to a contradiction with his experiment (because sometimes a single photon should lead to 2 clicks, sometimes 0, but QM always predicts 1). Where I get a bit confused is how the jump is made to non-locality. He uses a chain of logic to get this, but it seems to me that non-realistic interpretations are not ruled out.

I don't think non-realism can ever be brought down? I'm still a bit confused but this sentence by him in a paper that just came out today, does make it a bit clearer and is consistent with what you wrote:

If the decision happens at detection and D(0) and D(1) are space-like separated, then nonlocal coordination is required in order to ensure conservation of the energy in each single quantum event (that is, avoid that sometimes both detectors fire together provoking "one photon, two counts", and sometimes none of them fires, provoking "one photon, no count").

By contrast assuming decision at the beam-splitter BS1 permits to escape nonlocality in single-particle interference experiments (Figure 2), but on the price of assuming de Broglie's "empty waves", that is, entities propagating within space-time that do not carry energy and momentum and are in principle inaccessible to observation. Apparently, a likely subconscious desire to fight nonlocality without giving up the conservation of energy contrived Einstein to move from decision at detection to decision at the beam-splitter. And the move brought about the more complicated EPR argument.

Interestingly, in this quote he appears to suggest that the "pilot wave" inevitably leads to "many worlds" or at least, that Bohmians can't provide good arguments for opposing "many worlds"? He writes:

This interpretation ("many world") denies both Principles A and Q, and therefore is the consequent continuation and fulfillment of the "empty wave" program. It is important to be aware of the fact that if one accepts decision at the beam-splitter and "empty waves" one rejects (without realizing it) the Principles A and Q, and then one will not be able to oppose "many worlds".

Nonlocality at detection and conservation of energy: Was Einstein looking for an "epistemic" interpretation, a "superdeterministic" one, or both?
http://lanl.arxiv.org/pdf/1205.4451.pdf

 

[akhmeteli]

Is anyone familiar with Suarez's papers in this area? I've posted his most recent and pertinent papers on the topic below and even though I read them all, I'm still having trouble understanding his arguments:

Single-photon space-like antibunching
http://lanl.arxiv.org/pdf/1204.1712.pdf

The "forthcoming publications" include the following:

"Empty waves", "many worlds", "parallel lives" and nonlocal decision at detection
http://lanl.arxiv.org/pdf/1204.1732.pdf

Interestingly, the PBR theorem is also mentioned in his most recent paper:
Decision at the beam-splitter, or decision at detection, that is the question
http://lanl.arxiv.org/pdf/1204.5848.pdf

Let me note the following:

1) For some mysterious reason, Gisin does not claim anything "loophole-free", Suarez does.
2) It looks like Suarez' articles that you quote are unpublished.

Furthermore, I don't believe there is any "loophole-free" evidence of nonlocality in Suarez' articles or in the experiment by Gisin e.a. Indeed, even according to Suarez, there is evidence of nonlocality only if we assume "collapse at detectors":

"As it is well known, according to standard quantum mechanics which detector clicks (the outcome) becomes determined at the detection. In fact, most physicists share this view also referred to as "the collapse of the wavefunction at detection" by the Copenhagen (standard) interpretation. "Outcome's decision at detection" shall be the basic assumption in this paper." (http://lanl.arxiv.org/pdf/1204.1732.pdf )

I believe this is a loophole in Suarez' reasoning. Let me remind you that
1) “no positive experimental evidence exists for physical state-vector collapse” (M. Schlosshauer, Annals of Physics, 321 (2006) 112-149))
2) collapse and unitary evolution (dynamics) of quantum mechanics are mutually contradictory (see, e.g., http://plato.stanford.edu/entries/qt-measurement/ and references there)

 

[bohm2]

Let me note the following:

1) For some mysterious reason, Gisin does not claim anything "loophole-free", Suarez does.
2) It looks like Suarez' articles that you quote are unpublished.

I'm still lost why he claims "loophole-free" but the first paper which seems to serve the basis for his arguments is published in Physics Letters A (May 11/12):

Single-photon space-like antibunching
http://www.sciencedirect.com/science/article/pii/S0375960112005646

 

[akhmeteli]

I'm still lost why he claims "loophole-free" but the first paper which seems to serve the basis for his arguments is published in Physics Letters A (May 11/12):

Single-photon space-like antibunching
http://www.sciencedirect.com/science/article/pii/S0375960112005646

Yes, but there are no "loophole-free" claims in the published article (I should have said that the preprints signed by Suarez alone are apparently unpublished). As I said, for some reason, Gisin avoids such claims :-) Their joint paper may be the basis for Suarez' arguments, but not for his collapse assumption.

 

[San K]

Does the below paper demonstrate non-locality in a loophole-free manner?

http://physics.nist.gov/Divisions/Div844/publications/migdall/psm96_twophoton_interference.pdf

 

[akhmeteli]

Does the below paper demonstrate non-locality in a loophole-free manner?

http://physics.nist.gov/Divisions/Div844/publications/migdall/psm96_twophoton_interference.pdf

As far as I know, experts agree that there has been no loophole-free demonstration of nonlocality so far. Do the authors of the article you quote claim such demonstration?

 

[San K]

As far as I know, experts agree that there has been no loophole-free demonstration of nonlocality so far. Do the authors of the article you quote claim such demonstration?

the authors do not claim...loophole-free...

i was asking a general question, to understand loopholes, namely - what is the loophole in two-photon (or any entangled particle) experiments? such as in the paper or even in the delayed choice quantum eraser etc.

the paper says

"two-photon interference effects can be observed even when the optical paths in the interferometer have very different lengths, and the photons do not arrive at the beam splitter at the same time"

the interference, it seems, is happening non-locally. what is the loophole (for QE) in such experiments?

does it have to do with temporal resolution of the coincidence counter?

 

[akhmeteli]

the authors do not claim...loophole-free...

i was asking a general question, to understand loopholes, namely - what is the loophole in two-photon (or any entangled particle) experiments? such as in the paper or even in the delayed choice quantum eraser etc.

the paper says

"two-photon interference effects can be observed even when the optical paths in the interferometer have very different lengths, and the photons do not arrive at the beam splitter at the same time"

the interference, it seems, is happening non-locally. what is the loophole (for QE) in such experiments?

does it have to do with temporal resolution of the coincidence counter?

I don't think I have to sort it out - they don't even claim loophole-free evidence of nonlocality, and experts agree that there is no such loophole-free evidence. Suarez does claim such evidence, and I explained why I cannot believe him.

As for loopholes in general in experiments with entangled particles, there is the detection loophole, locality loophole, and so on.

 

[stevendaryl]

The Schrodinger cat paradox is resolved by the fact that the entanglement (superposition of states) is broken at some point/event after emission from the radioactive decay. We may not know exactly what that point/event is however there is no paradox.

I don't see entanglement is being any kind of resolution to the paradoxes of quantum mechanics, except that it shows why we could never observe macroscopic superpositions (DeadCat + LiveCat).

 

[San K]

I don't see entanglement is being any kind of resolution to the paradoxes of quantum mechanics, except that it shows why we could never observe macroscopic superpositions (DeadCat + LiveCat).

i think it depends upon how you look at it steve.

the cat is never in superposition (of dead and alive). the superposition breaks of at some earlier event.

depends upon how you define a paradox. it's an issue of semantics.

as a quick illustration - for example the paradoxes in relativity are not paradoxes, because they were resolved at the time of creation of the paradox. same is the case with quantum mechanics, in my opinion.

per my definition/understanding of paradoxes...there are NO unresolved/true/genuine paradoxes in physics

in any case... this is trivial/not so important..

 

[San K]

Suarez does claim such evidence, and I explained why I cannot believe him.

agree with you

 

[San K]

Suarez is asking: at what point is the superposition of states decided? Is it done at the point in the apparatus where the beamsplitter appears? Or is it done later, when the final configuation is known and the particle is detected?

i would think the decision is at the time of detection because events after the beam-splitter (such as delayed eraser) can still change the behaviour/properties of the photon

 

[stevendaryl]

the cat is never in superposition (of dead and alive). the superposition breaks of at some earlier event.

I think we might have a disagreement about what entanglement involves. The way I understand entanglement, you have correlations that form between the state of a small system (an electron or a cat) and the environment, which includes electromagnetic waves, gravitational waves, noise, etc. The state of the cat becomes correlated with the state of the rest of the world. There's still a superposition, but we can no longer practically observe interference effects (which is the way that a superposition can be distinguished from a mixed state).

 

[yoda jedi]

I don't think non-realism can ever be brought down? I'm still a bit confused but this sentence by him in a paper that just came out today, does make it a bit clearer and is consistent with what you wrote:


Nonlocality at detection and conservation of energy: Was Einstein looking for an "epistemic" interpretation, a "superdeterministic" one, or both?
http://lanl.arxiv.org/pdf/1205.4451.pdf

your question is:

Does the quantum state represent reality or our knowledge of reality?

in ψ-epistemic models, there exist distinct quantum states that correspond to overlapping probability distributions in that case the quantum state can considered to be truly epistemic, that is, a representation of an observer’s knowledge of reality rather than reality itself (incomplete, hidden variables).
in ψ-ontic models, distinct quantum states correspond to disjoint probability distributions over the space of ontic states in the theory is consistent with only one pure quantum state and can be complete and incomplete (ψ-supplemented, hidden variables).

the ψ-complete view is the interpretation that takes the quantum state alone to be a complete description of reality (not hidden variables).


.

 

[bohm2]

My major problem is with his "loophole-free" demonstration of non-locality claim. As was pointed out above, to date, there has never been a completely "loophole-free" demonstration of non-locality. Suarez claims that the experiment in the first link of the first post is such a case and it doesn't rely on Bell's theorem. The only stipulation is that decision is determined at detection versus at beam-splitter. The author writes:

Taking account of the previous analysis, we can conclude that Bell-type experiments prove nonlocality only as far they are implemented assuming decision at detection. Since in the Bell-type experiments realized to date one payed attention that Alice and Bob are spacelike separated, but one didn't care about the separation of Alice's detectors for themselves (respectively Bob's ones), one can certainly say that such experiments demonstrate nonlocality between Alice's and Bob's detections. But it is also true that the detection loophole is not yet closed. By contrast one can say that the experiment in [1, 2] demonstrates nonlocality in a more straightforward way, and (as discussed in [2]) without loopholes. Additionally, this experiment demonstrates something more than nonlocality, that is: Without nonlocality we could not have the most fundamental principle ruling the material world, the conservation of energy. Quantum physics has certainly to do with information, but fortunately also with physics.

Decision at the beam-splitter, or decision at detection, that is the question
http://lanl.arxiv.org/pdf/1204.5848.pdf

 

[bohm2]

This is another recent paper claiming "loophole-free":

The three major loopholes are based on: hidden communication between the observers (locality loophole), possible influences from or on the choice of measurement settings (freedom-of-choice loophole) and unfair sampling of the measured ensemble (detection loophole). In our experiment—for the first time in any experiment—all of these loopholes are closed simultaneously. Thereby, we exclude—for the first time loophole-free—an important class of local realistic theories considered by EPR...Simultaneously closing these three major loopholes in a single experiment excluding an important sub-class of local realistic theories is a major step forward, particularly with regard to future loophole-free experiments testing Bell inequalities, which would exclude all local realistic theories.

However, they also write:

What we cannot exclude, as with any experiment, is the possibility that an earlier common cause in the overlap of the backward light cones of the two events (emission and choice of the setting) influences the two events in a correlated manner. We believe, however, that such a hypothesis is outside the scope of what can in principle be tested experimentally.

Loophole-free Einstein–Podolsky–Rosen experiment via quantum steering
http://iopscience.iop.org/1367-2630/14/5/053030/pdf/1367-2630_14_5_053030.pdf

 

[akhmeteli]

This is another recent paper claiming "loophole-free":

From what they say themselves, it's clear that what they did (I did not check their claims though) is a far cry from loophole-free demonstration of violations of the Bell inequalities and, therefore, from ruling out all local realistic theories.

 

[bohm2]

From what they say themselves, it's clear that what they did (I did not check their claims though) is a far cry from loophole-free demonstration of violations of the Bell inequalities and, therefore, from ruling out all local realistic theories.

By demonstrating quantum steering that is loophole-free the authors seem to be arguing that if one takes a realist stance then their experiment shows a nonlocal property that is stronger than nonseparability but not quite ruling out Bell-nonlocality. This is based on the paper where they argue that:

steerability is a distinct nonlocal property of some bipartite quantum states, different from both Bell-nonlocality and nonseparability...(and prove)...that steerability is strictly weaker than Bell-nonlocality as well as being strictly stronger than non-separability.

Steering, Entanglement, Nonlocality, and the EPR Paradox
http://www98.griffith.edu.au/dspace/bitstream/handle/10072/18284/46888_1.pdf?sequence=1

 

[akhmeteli]

By demonstrating quantum steering that is loophole-free the authors seem to be arguing that if one takes a realist stance then their experiment shows a nonlocal property that is stronger than nonseparability but not quite ruling out Bell-nonlocality. This is based on the paper where they argue that:

Steering, Entanglement, Nonlocality, and the EPR Paradox
http://www98.griffith.edu.au/dspace/bitstream/handle/10072/18284/46888_1.pdf?sequence=1

Again, in the experimental article, they just claim: "we exclude—for the first time loophole-free - an important class of local realistic theories considered by EPR." So they definitely do not exclude all local realistic theories.

 

[audioloop]

Can mechanics be improved?|Does
the previous conclusions mean that mechanics
is the ultimate theory and will not experience any further
improvement in the future? Not by any means. Quan-
tum physics has still to solve for instance the so called
\measurement problem"

I don't think the measurement problem (cat paradox) has been resolved at all.

i agree.
---------
and related/connected to:
(regardeless of loopholes)

Is anyone familiar with Suarez's papers in this area? I've posted his most recent and pertinent papers on the topic below and even though I read them all, I'm still having trouble understanding his arguments:

Decision at the beam-splitter, or decision at detection, that is the question
http://lanl.arxiv.org/pdf/1204.5848.pdf

that's why I say:

Holism is more than Non-Separability as Contextuality is more than Non-Locality
---
"a physical theory is holistic if and only if it is impossible in principle to infer the global properties,
as assigned in the theory, by local resources available to an agent, there is no way we can find out about it using only local means, i.e., by using only all possible non-holistic resources available to an agent. In this case, the parts would not allow for inferring the properties of the whole, not even via all possible subsystem property determinations that can be performed"

Seevinck. (Epistemological Holism, physical property holism).
(unlike of Ontological Holism, Nonseparability).


how, when and what it can posit the cause of explanation (determination) of values
or are values just "parts" of a single fact or process (as matter of fact, not so composed) ?Hierarchical Status

Holism -> Non separability -> Contextuality -> Nonlocality

Syntactical Reality
.

or/and maybe how to infer the properties (value of parts) from the whole.------

Is anyone familiar with Suarez's papers in this area? I've posted his most recent and pertinent papers on the topic below and even though I read them all, I'm still having trouble understanding his arguments"Empty waves", "many worlds", "parallel lives" and nonlocal decision at detection
http://lanl.arxiv.org/pdf/1204.1732.pdfDecision at the beam-splitter, or decision at detection, that is the question
http://lanl.arxiv.org/pdf/1204.5848.pdf

decision: before, beginning, interim, or detection.

"Empty waves", "many worlds", "parallel lives" and nonlocal decision at detection
http://lanl.arxiv.org/pdf/1204.1732.pdf

..."The experiment does not require Bell's inequalities and is loophole-free"...

cos bell`s is about before emision (pre-existing properties).but i don't follow that argument (stricto sensu) because in any case, if one argues that the non-locality is in the detection, it can be said that comes from the beginning and there is no way to establish or prove (or disprove) that assertion.

 

[San K]

My point is that the point of Schrodinger was not to illustrate (or better understand) entanglement, but to show that extrapolating quantum mechanical conclusions to the macro world leads to absurdity.

agreed martin. that's what I was saying. however I think many people wrongly believe that there is an unresolved/un-solved paradox.

for example the twin paradox, in relativity, is a resolved paradox, because we have an explanation for it. thus it is not really a paradox.

it's just a means to illustrate.

same with Schrodinger's cat

 

[audioloop]

From what they say themselves, it's clear that what they did (I did not check their claims though) is a from -free demonstration of violations of the Bell inequalities and, therefore, from ruling out all local realistic theories.

and re-stated

..."Simultaneously closing these three major loopholes in a single experiment excluding an important sub-class of local realistic theories is a major step forward, particularly with regard to future loophole-free experiments testing Bell inequalities, which would exclude all local realistic theories"...
Loophole-free Einstein-Podolsky-Rosen experiment via quantum steering
http://arxiv.org/ftp/arxiv/papers/1111/1111.0760.pdf
-----
other

Detection loophole in Bell experiments: How postselection modifies the requirements to observe nonlocality
http://pra.aps.org/abstract/PRA/v83/i3/e03212
http://arxiv.org/pdf/1010.1178.pdf

"A common problem in Bell-type experiments is the well-known detection loophole: if the detection efficiencies are not perfect and if one simply postselects the conclusive events, one might observe a violation of a Bell inequality, even though a local model could have explained the experimental results. In this paper, we analyze the set of all postselected correlations that can be explained by a local model, and show that it forms a polytope, larger than the Bell local polytope. We characterize the facets of this postselected local polytope in the Clauser-Horne-Shimony-Holt scenario, where two parties have binary inputs and outcomes. Our approach gives interesting insights on the detection loophole problem."

...One of these loopholes is known as the detection loophole [7]. Typically, in photonic experiments the detection
efficiencies are not perfect, and one usually post-selects the detected events to show a violation of a Bell inequality. However, there might exist a model that exploits the detector inefficiencies to reproduce the experimental data [7, 8], in perfect agreement with Bell’s assumption of local causality [1]. In order to circumvent this problem, one usually resorts to the fair sampling assumption, that the detected particles are representative of all those emitted from the source, but this additional assumption is certainly not satisfactory. Closing the detection loophole would require either improving the detection efficiencies of the detectors used in Bell experiments, or finding Bell inequalities that are more robust to detection inefficiencies, as reported in [9–14]. Although the known necessary detection efficiencies are still quite high, a photonic detection-loophole-freeBell experiment seems possible in the near future...

dont know if loopholes are the ultimate answer but as they say Brunner, Wiseman, Zeilinger and others
"is a major step forward"

Efficiently heralded sources for loophole-free tests of nonlocality and singlephoton vision research.
Paul G. Kwiat, Kevin T. McCusker, Rebecca M. Holmes and Bradley Christensen.

...While the timing loophole can easily be closed in such a system by moving the detectors sufficiently far apart, closing the detection loophole is more difficult...

 

[bohm2]

This is an interesting paper that came out today that sort of relates to this thread:

Due to experimental limitations, fair sampling has been assumed in nearly every Bell experiment performed to date; a few exceptions include (5-8). To date, it has never been possible to avoid this assumption with photons due to the absence of efficient sources and detectors. Here we report the first Bell experiment with photons that does not rely on any fair-sampling assumption...We note that with our experiment, photons are the first physical system for which each of these three assumptions has been successfully addressed, albeit in different experiments.

Bell violation with entangled photons, free of the fair-sampling assumption
http://lanl.arxiv.org/ftp/arxiv/papers/1212/1212.0533.pdf

 

[nanosiborg]

This is an interesting paper that came out today that sort of relates to this thread:

Bell violation with entangled photons, free of the fair-sampling assumption
http://lanl.arxiv.org/ftp/arxiv/papers/1212/1212.0533.pdf

The abstract is, I think, not properly phrased.

The violation of a Bell inequality is an experimental observation that forces one to
abandon a local realistic worldview, namely, one in which physical properties are
(probabilistically) defined prior to and independent of measurement and no physical influence
can propagate faster than the speed of light.

I think it would be better to say that the violation of a Bell inequality is an experimental observation that forces one to abandon a certain way of modelling quantum entanglement, and that this doesn't necessarily inform regarding a local realistic worldview in which physical properties exist prior to detection and physical influences don't propagate faster than the speed of light.

Just a semantic point, but that's often the case with interpretation, or misinterpretation, as the case may be.