Talk:Delayed-choice quantum eraser/Archive 6

Suggest we change graphs to real data
How about using this one. I think that a somewhat sloppy reproduction of the actual data could avoid the need to call the information simulated.
 * R04 is a problem. The output was not identical, but displaced. Stigmatella aurantiaca (talk) 00:05, 24 February 2014 (UTC)


 * I don't remember that part. What causes the displacement? P0M (talk) 00:09, 24 February 2014 (UTC)


 * Article didn't say. We could write to ask. "There is no significant difference between the curves of R03 and R04 except the small shift of the center." Stigmatella aurantiaca (talk) 00:21, 24 February 2014 (UTC)


 * I hadn't noticed the sentence you quoted. I think it is easy to explain as due to the path length differences. I can't see any reason for a major phase change such as occurs between the two interference patterns. It will be easy to give the diagrams a "slight shift of the center." Do you have a preference for the jpg or the svg version? P0M (talk) 01:28, 24 February 2014 (UTC)


 * I can work with either, but the JPG "looks like" a copyright violation and will eventually be deleted. How did you create the SVG? I'm looking at the markup in Notepad++ and am a bit puzzled. Stigmatella aurantiaca (talk) 07:11, 24 February 2014 (UTC)


 * The remnants of the original drawing in the JPG will trigger alarm bells in the minds of any reviewer. Few if any will bother to compare with the drawings in the original paper before marking it with a delete template. Stigmatella aurantiaca (talk) 07:16, 24 February 2014 (UTC)


 * The SVG is a tracing of the original curve, then the tracing was subjected to a "trace bitmap," and then simplified. If that isn't far enough from the original I could use graph paper and do one freehand. P0M (talk) 07:45, 24 February 2014 (UTC)


 * Ah! Now I understand. Anyway, that doesn't bother me, but could you zero out the baselines? Kim et al.'s Figure 3 and Figure 5 zero count baselines are each elevated about 10 units from the bottom. I would be doing the adjustments myself when I create the dot patterns, but it would be better if the drawings and the simulated coincidence counts matched. Stigmatella aurantiaca (talk) 07:52, 24 February 2014 (UTC)


 * At first I didn't read carefully and made the diagrams worse. Now I see what needs to be done. The images SVG images I posted are still wrong. Tomorrow I'll fix them.P0M (talk) 09:16, 24 February 2014 (UTC)
 * Done.P0M (talk) 13:53, 24 February 2014 (UTC)

I've uploaded correlated count simulations based on your graphs. They don't look very convincing, and after checking your tracings against the originals, I see that the peaks and troughs do not line up well. Stigmatella aurantiaca (talk) 03:28, 26 February 2014 (UTC)
 * Give me until the weekend. I can work on both figures. Stigmatella aurantiaca (talk) 03:41, 26 February 2014 (UTC)
 * Uploaded revised SVG and GIF. Kim et al. weren't careful to illustrate at a common scale or to use a consistent baseline, so the graphs needed to be zoomed varying amounts in the horizontal and vertical dimensions as well as being cropped to eliminate the black bars in the GIFs. Stigmatella aurantiaca (talk) 08:27, 27 February 2014 (UTC)
 * It looks beautiful now. Thank you.P0M (talk) 13:59, 27 February 2014 (UTC)

Note that double-slit interference isn't limited to atomic-scale entities?
I think it would be good to note that double-slit interference is not limited to "atomic scale" entities (which is what the article currently implies but doesn't say).

Some references that we could use in this article re double-slit interference with C60 molecules:

http://physicsworld.com/cws/article/news/1999/oct/15/wave-particle-duality-seen-in-carbon-60-molecules

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3104521/ — Preceding unsigned comment added by 130.56.241.250 (talk) 01:50, 5 September 2014 (UTC)

Maybe another explanation?
Figure 2 assumes that an individual photon will obey the reflection principle as to the angle of reflection. This classical principle relies on the Fermat's principle, AFAIR, which is a special case of the principle of least action. The latter, according to Feynman, demonstrates why in the classical limit (macroscale) quantum events act according to classical principles.

But either you assume that the universe is at all deterministic and thus the path "taken" (realistically speaking, as in the formalism) by a particle will be very classical, to the extent of not departing a slightest bit from a natural course without a cause, OR you assume that other close courses are still possible (or maybe even single point-alike departures from a generally classical, continuous path). In the first case you are a determinist and a realist. In the latter case you think like a Copenhagen adept, but then you must assume that, consequently, light can exit a mirror -- or a 50% beam splitter -- in several ways. Furthermore, even a determinist will accept a deterministic chaos (like with natural dispersion of light on non-ideal objects) which effectively makes the trajectory light is taking not obvious; the angle can be close to the one assumed in Figure 2, but eventually it can also be slightly different. (Also with Picture 1, is it certain that a photon cannot change its direction, i.e. x/y momentum, by leaps when close to the detector? How can you conclude with certainty, i.e. deterministically, here, if you -- as many today's physicists do -- reject strict cause-and-effect at bottom of the universe?) Or maybe you assume that Feynman's path integral formalism implies total determinism between A and B, but then determinism implies realism.

With many photons the principle of reflection might be preserved but is its strict preservation in case of a single photon and detector so obvious(?).

With such picture in mind the following explanation can be suggested: when light goes through just one mirror or beam splitter -- let me call them in general "beam changers" -- there is no interference. Examples are D4 (via BSb) and D3 (via BSa). The other two cases, where interference actually occurs, involve more than one beam changer on the way, actually three if I see correctly now (sorry, a bit in a hurry...). So if you imagine different paths taken by light when leaving one beam changer, and then different paths i.e. dispersion when leaving the other one, these two might cross each other and produce interference. This is like a single bulb producing light in all directions not crossing each other, but when an additional object reflects these beams they may cross each other. The key observation is that there is no definite beam when leaving a beam changer but several ones.

In such terms the experiment could be explained without any reference to the high-level "information" about paths and the whole problem with complementarity and quantum erasure.

The whole way of speaking about such experiments is BTW misleading, because it is like implying a deist God sitting and thinking about high level things like paths and memory of something, whereas actually one can just say that forcing a certain polarization results in particle-alike behaviour and that is all, which is nothing about any "information having" of ours (aren't we confusing cause and effect here in order to confirm a previously established principle, which was luckily true, once again). 178.42.114.180 (talk) 00:07, 18 October 2014 (UTC)

Detector D0
The idea of Detector D0 has not been fully explained, so the reader like me don't understand how signal photon is recorded at detector D0. Is it somewhat like photographic plate which records position of signal photon when it lands on detector D0? I mean, if detectors D1/D2 are removed and if ALL of the idler photons are observed at D3/D4, then will human eye see only 2 bands (no interference pattern) at detector D0? What if idler photons are observed at D3/D4 after 1 year? Will we see 2 bands at detector D0 during this year? Such questions arise in the mind of the reader because idea of detector D0 has not been fully explained in this article. This article needs improvement. AbhiRiksh (talk) 10:33, 30 September 2015 (UTC)

Very exciting at first but misleading from the start
I saw a few YouTube videos about it and they claim that you can see an interference pattern or no interference pattern astonishingly depending on whether you let the photons go to the individual slit detectors or through the eraser. But it's not true - they should just all tell you right from the start that there's absolutely no interference pattern formed on the screen at any point. 174.118.34.7 (talk) 19:29, 25 November 2016 (UTC)

Description of the Kim et al 2000 experiment is horrible
The section on the Kim et al 2000 experiment is written horribly. It jumps immediately into the experimental procedure, mixing the essential details of the setup with experimental minutiae. The section needs a preface subsection giving an overview of the setup. — wing  gundam  20:47, 26 November 2016 (UTC)

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Error?
In Introduction section: ''Lest there be any misunderstanding, the interference pattern does disappear when the photons are so marked. However, the interference pattern reappears if the which-path information is further manipulated after the marked photons have passed through the double slits to obscure the which-path markings. This seem absurd: if the interference does disappear, how can reappears''? I think that it disappear before, then reappear--93.39.9.205 (talk) 07:46, 15 April 2017 (UTC)


 * I don't see any contradiction there. The interference pattern disappears, but it will reappear if the which-path information is erased. 143.252.80.100 (talk) 11:31, 3 May 2017 (UTC)

Please describe why R1 and R2 are shifted so it looks like the union should be R3 or R4.
As near as I can tell the only difference between R1 & R2 should be chance. Did the photon turn or go straight at the beam splitter. I would expect the inference patterns for R1 & R2 to be exactly the same, and I would expect if I were to combined R1 & R2 data to see the exact same results. But we don't see that at all. We see one diffraction pattern is shifted compared to the other. The most likely explanation is more of the photons detected in D1 went through the right slit, and more of the photons measured in D2 went through the left slit. If say 5 % more light passed through the right slit, that would tend to shift the node pattern to the right, and visa versa. Since the union of R1 & R2 looks like R3 & R4, this leads to the very dissatisfying result of not at all being certain what one would see if the experiment was done more precisely, so D1 v.s. D2 provided no useful information about which slit. A second possibility is there are two orthogonal measurements happening. Is it slit 1 or 2, is wave 1 in phase with wave 2 or out of phase. The out of phase diffraction pattern would always be shifted compared to the in phase diffraction pattern. So if say D1 is triggered more often when the waves are in coherent, and D2 is triggered more often when the waves are out of phase again you would expect the shifted patterns. That makes sense, but begs the question why would not be coherent. One always does double slit diffraction experiments with a coherent light source. The fact we don't see a diffraction pattern on the left without filtering indicates we don't have a coherent light source. So does that mean we didn't start off with a coherent light source, or did the quantum entanglement cause us to lose coherence? Here I have two different possible explanations, further clarification would really help.Bill C. Riemers (talk) 17:52, 4 October 2017 (UTC)

Implications for Interpretations of Quantum Mechanics
Should we discuss here the somewhat obvious implication that Copenhagen interpretation and its derivatives that use wave-function collapse on D0 can not be true in this experiment and thus rejected? Many Worlds interpretation, on the other hand, is compatible with the experiment. I am actually not sure if there is any other interpretation that compatible as well.

MxM (talk) 20:04, 22 November 2019 (UTC)

Interpretation
I want to make three comments:

JohnGFFrancis (talk) 20:50, 3 December 2019 (UTC)
 * 1) According to the Wikipedia entry on Spontaneous parametric down-conversion it is only 4 photons in 106 that get down converted so to get any subsequent interference from the slits we should surely assume that at the BBO there is a single path. This should be clarified on the diagram.
 * 2) There is no need to refer, several times, to individual (separate) photon partical paths as if they exist. Experiments such as these show that they don't, as believed by Williams (unless one adopts the de Broglie-Bohm Interpretation). Photons only appear as particles at detectors, where the wavefunctions get reduced (non-local variables determining correlated polarisations, etc.).
 * 3) Most importantly, there is no need for any suggestion of retrocausality. Whatever happens later to the idler photon cannot change what happened at D0. It only changes the interpretation we put on the D0 recording.

Consensus: no retrocausality
It says here: "Similarly, in the case when D0 precedes detection of the idler photon, the following description is just as accurate: "The position at D0 of the detected signal photon determines the probabilities for the idler photon to hit either of D1, D2, D3 or D4"." I don't think, this is correct: On D0, there is some probability x of the photon arriving as particle and a probability of (1-x) of it arriving as wave. This has to be determined when hitting D0 and not later. But x depends on the apparatus that the entangled photon has to pass through on the way to the detectors D1, D2, D3 and D4 (there is no need for x to be exactly 50%). Thus the first photon does still need some information about what the future will bring for it's counterpart. Otherwise, it would not be able to "decide" for the correct ratio between "arrive as wave" and "arrive as particle". Epaminaidos (talk) 12:40, 20 February 2020 (UTC)

Not right
This says nothing about the delayed choice quantum eraser experiment in only mentions the delayed choice double slit experiment and describes how that works and what is shows the delayed choice quantum eraser experiment is different and nothing is said about it this is wrong 107.77.232.138 (talk) 01:12, 5 January 2022 (UTC)

A consideration not mentioned in this article
In the paper "Quantum erasure with causally disconnected choice" by Xia-Song-Ma, Johannes Kofler et. al., describing their execution of this experiment where the measurement and subsequent preservation or erasure of the which-way information is done 144KM removed from the primary detector, they propose another way of looking at this: "Our results demonstrate that the viewpoint that the system photon behaves either definitely as a wave or definitely as a particle would require faster-than-light communication. Because this would be in strong tension with the special theory of relativity, we believe that such a viewpoint should be given up entirely." Link to the paper: Quantum erasure with causally disconnected choice (pnas.org) 24.193.151.211 (talk) 16:04, 7 August 2022 (UTC)

Issue with language used under the "Against consensus" heading ....
Under the "against consensus" heading, the article refers to "Eberhard's proof." The words "Eberhard's argument in opposition" would be more appropriate and less biased or conclusive. Wheeler's thought experiments, and various laboratory setups that test his hypotheses, do not suggest retro-causality or an inference that future (or present) measurement decisions alter the past. 2600:8801:BE31:D300:DE8:C9A4:BA1B:94B1 (talk) 19:08, 29 September 2022 (UTC)

the cause of the resurrection of the interference fringes
The result of obscureing the photons is R01+R02. As written in the original paper, there is no interference fringe at R01+R02 (for some reason the graph for R01+R02 is not quoted on this page). Therefore, the cause of the resurrection of the interference fringes is not the obscure of the photon mark. The process of extracting R01 and R02 from R01+R02 is the cause of the revival of interference fringes. This process cannot be executed if the path is known. D1 and D2 are part of the Mach–Zehnder interferometer. SPDC also disturbs the phase randomly. Think about what it means physically to extract R01 and R02 from them.114.170.87.214 (talk) 05:37, 9 January 2023 (UTC)

If multiple conditions are different and the experimental results are different, a scientific basis is required to determine which of the conditions is the cause. If you do not indicate the source of the scientific basis, it corresponds to original research. 114.170.87.214 (talk) 05:43, 9 January 2023 (UTC)

Figure 1. Confusing description of top diagram
@L3erdnik

In the top diagram there is only one apparatus - in the bottom left (green block). Photons that emerge from the top of it go up (red path), photons that emerge from the side of it go on the blue path. The paragraph states opposite, unless I miss something:

"In the top diagram, it seems as though the trajectories of the photons are known: If a photon emerges from the top of the apparatus, it seems as though it had to have come by way of the blue path, and if it emerges from the side of the apparatus, it seems as though it had to have come by way of the red path"

Merlin.anthwares (talk) 14:31, 23 September 2023 (UTC)


 * You seem to be mistaking the "apparatus" mentioned in the text, which refers to the whole setup (laser, beam-splitter and two mirrors) with the beam-splitter (green block on the bottom-left). Carolus59 (talk) 17:09, 23 September 2023 (UTC)
 * Thank you for the clarification! If "apparatus" is the whole setup, then it makes sense Merlin.anthwares (talk) 17:50, 23 September 2023 (UTC)

Intrinsically Non-classical?
The article states: "These precursors use single-photon interference. Versions of the quantum eraser using entangled photons, however, are intrinsically non-classical."

It should be explained why entanglement is intrinsically non-classical. A produced pair of spin-up and spin-down electrons for example may have measurable quantum properties, but according to QM so does everything that exists. Just because entangled particles are useful in certain QM experiments does not imply anything about their intrinsic nature; if one used entangled particles to simply demonstrate the effects of gravity, it would not necessarily imply gravity is a QM construct. Niubrad (talk) 13:31, 11 January 2024 (UTC)