Double-slit experiment with photons vs electrons

[TrickyDicky]

Isn't light, in the sense of flow of photons, a macroscopic 'object' in the same sense as matter is when large collection of atoms pass beyond the macroscopic limit?

I believe it was you that in a different thread stated the obvious fact that the sooner we get rid of the concept of particles as fundamental entities the better. QFT goes in this direction but in an ambiguous enough way that many physicists for instance in high energy physics still disregard the field conception as something "philosophical" and still consider particles as "the real thing"( meaning fundamental) despite the fact the standard model of particle physics is sustained by QFT.

 

[bohm2]

However, whether or not the community should put resources into closing the fair sampling loophole is an obsolete question right now. The community has closed that loophole in Phys. Rev. Lett. 111, 130406 (2013) by Christensen et al. ("Detection-Loophole-Free Test of Quantum Nonlocality, and Applications", http://prl.aps.org/abstract/PRL/v111/i13/e130406).

Yes, I'm aware that all 3 loopholes have been closed (although not at same time). Maybe I'm not understanding Khrennikov's argument but from what I have read, I was under the impression that his argument is more subtle. Using a Bohrian perspective (experimental contextuality), he argues that Bell went wrong even before the issue of loopholes. Khrennikov is arguing that we are wrong to use a common probability space for different settings of an apparatus. Hence, his argument for a non-Kolmogorovean probability model. Having said that, I don't really understand how that relates to the recent closing of the detection loophole. I'm confused whether closing of the detection loophole obviates his argument. I really don't understand his mathematical argument but if the detection loophole is experimental evidence against his model, why does he claim that his argument holds regardless of the issue of loopholes. Apparently, many physicists had trouble understanding his point at the conferences also.

 

[marmoset]

It is interesting that a photon wavefunction very closely related to the Maxwell field can be defined (as mentioned earlier in the thread). It is very interesting that the two photon wavefunction built from these one photon wavefunctions reproduces previous results of classical coherence theory. The papers can be found here http://arxiv.org/abs/0708.0831, http://arxiv.org/abs/quant-ph/0605149.

 

[Cthugha]

I suggested that modeling radiation and matter in terms of nonlinear waves might help but then I realized that the QM formalism(let alone the postulates) doesn't even allow nonlinear operators(as long as we hold on to Hilbert space), so until (and if) that formalism is developed it is not very fruitful to explore that path(or is it?).

But people already checked for violations of Born's rule and the presence of higher-order terms. See "Ruling Out Multi-Order Interference in Quantum Mechanics", Science 23 July 2010: Vol. 329 no. 5990 pp. 418-421 or check the ArXiv version here: http://arxiv.org/abs/1007.4193. They have not found any deviations.

I really don't understand his mathematical argument but if the detection loophole is experimental evidence against his model, why does he claim that his argument holds regardless of the issue of loopholes. Apparently, many physicists had trouble understanding his point at the conferences also.

I think he discusses the detector efficiency point because of the foundations of his model. While his thoughts on Bell might be elegant, he still has the problem that he proposes a classical-field-like model and has to explain somehow why we see evidence for single photon states in antibunching experiments. Here, he can only blame the detectors and claim that the physics of detectors is not properly understood and more "ideal" detectors will help clarify. However, this is also the point most people do not buy. See also the above manuscript by the Weihs group (which may or may not have been directly motivated by ideas similar to Khrennikov's) on the validity of the Born rule in terms of higher-order effects.

 

[f95toli]

on a related note - are Maxwell's equation valid for single photon?

Yes, at least much of the time. When designing equipment that is used for single photon experiments you can always(?) use Maxwell's equations for the design process. An obvious example would be the design of say microwave cavities similar to what is used by say Haroche's group for cavity-QED experiments. You can also use classical equations to calculate things like couplings strenghts etc. This makes our lives much easier since it means we can use conventiomal EM simulation software, and the designs still work for single photons (although you have to be cautious when interpreting the results).

It is also possible to quantize many classical expressions "after the fact", i.e. one can derive the equations for a given ransmission line using classical arguments and and then quantize the resulting Lagrangian.

 

[bohm2]

While his thoughts on Bell might be elegant, he still has the problem that he proposes a classical-field-like model and has to explain somehow why we see evidence for single photon states in antibunching experiments. Here, he can only blame the detectors and claim that the physics of detectors is not properly understood and more "ideal" detectors will help clarify. However, this is also the point most people do not buy. See also the above manuscript by the Weihs group (which may or may not have been directly motivated by ideas similar to Khrennikov's) on the validity of the Born rule in terms of higher-order effects.

I haven't read his paper yet, but he has published a paper arguing that bunching and anti-bunching for quantum systems can be represented in the classical signal framework. I'm not sure if his model is motivated by the above group but these authors were not referenced in his paper. I wish I had a stronger mathematical background because I have trouble making sense of these arguments but I do know that Khrennikov is a major player in the Emergent QM group that have had 2 previous conferences: See http://www.emqm13.org/ and http://www.univie.ac.at/hvf11/congress/EmerQuM.html

Classical signal viewpoint to bunching and anti-bunching
http://arxiv.org/pdf/1105.4268.pdf

 

[TrickyDicky]

But people already checked for violations of Born's rule and the presence of higher-order terms. See "Ruling Out Multi-Order Interference in Quantum Mechanics", Science 23 July 2010: Vol. 329 no. 5990 pp. 418-421 or check the ArXiv version here: http://arxiv.org/abs/1007.4193. They have not found any deviations.

Sure, I would not expect to see any deviation within their experimental limits, if it exists it is too small to be detected at the bound they use and certainly not unless the interference is tested on big enough molecules as they say in their closing lines.
We know that in the classical macroscopic world (i.e. in water waves)we observe nonlinear interference from highly nonlinear waves, it is to be expected that if there is any nonlinearity at the microscopic scale it has a very small effect.

 

[Cthugha]

Yes, at least much of the time. When designing equipment that is used for single photon experiments you can always(?) use Maxwell's equations for the design process.

To add to ehat has been said: From my experience you are ok using Maxwell's equation as long as you are interested in mean intensities and quantities related to them. As soon as you are interested in correlations (experiments using coincidence counting), Maxwell's equations will only work for coherent light.

I haven't read his paper yet, but he has published a paper arguing that bunching and anti-bunching for quantum systems can be represented in the classical signal framework.

That paper is not really about the problem at hand here. He shows that in his model boson-like entities show bunching and fermion-like entities show antibunching. This is well known and has been shown, e.g. for Helium 3 and Helium 4. It is more or less a consequence of sign changes when calculating probability amplitudes for events having these entities end up in the same state. His model reproduces these predictions. What he does not show is that his model can also show antibunching for boson-like entities under "blockade" conditions. For example a single atom will only emit a single photon at a time because one needs to reexcite it before it can emit again, so there is this blockade which makes a bosonic system behave like a fermionic one. The question of how to reproduce this effect using classical fields is the central one and in my opinion there is no classical field-like model doing that in a satisfying manner. Usually that is the point where those theories claim that common detector physics is wrong which is not convincing to me.

We know that in the classical macroscopic world (i.e. in water waves)we observe nonlinear interference from highly nonlinear waves, it is to be expected that if there is any nonlinearity at the microscopic scale it has a very small effect.

But it is pretty trivial that you get nonlinearities when going to media, no? Well, of course one can always go ahead and find a better bound in experiment.

 

[TrickyDicky]

But it is pretty trivial that you get nonlinearities when going to media, no?

Yes, it is implicit in my analogy that in the microscopic case the quantum vacuum may be considered a nontrivial nonlinear medium. This is theoretically expected as I commented previously above the Schwinger limit in QED, but I'm wondering if this kind of nonlinearity could be considered in principle also at low energies as a source of "wavefunction collapse behaviour". I'm taking this line of thought(just in case it rings some bell) from Nobel recipient Bob Laughlin ideas about the emergent quantum vacuum as a kind of phase of matter.

 

[San K]

Is it not just the double slit (or other interference experiments) but many other interactions?

where the equations used to model photon behavior are different from those used for electrons...