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Method and Apparatus For Transmitting Signals Faster than Light? (Based on EPR/QM)

  1. Jan 17, 2006 #1
    Method and Apparatus For Transmitting Signals Faster than Light?? (Based on EPR/QM)

    Method and Apparatus For Transmitting Signals Faster than Light?? (Based on EPR/QM)

    Does the following apparatus make sense? Please discuss and let me know where the logic or science is falling short, if it is falling short.

    45Revolver: Method and Apparatus for Transmitting Signals Faster than
    the Speed of Light

    Feel free to email me for the paper and the figures:
    REVOLVER45@gmail.com

    Consider an apparatus with a source for two interacting spin ½ photons
    at the center, as shown in Figure 1. On either side of the source is a
    double slit at distance d1, and beyond each double slit is a screen at
    distance d2.


    The two interacting spin ½ photons separate and travel in opposite
    directions. Each passes on through a double slit-double-slit1 and
    double-slit2, and an interference pattern is observed on each of the
    two screens, screen1 and screen2.


    Suppose then that a measurement device is then placed in front of the
    upper slit in the double-slit to the left of the photon source, as
    shown in Figure 2. Now photons must either go through the upper slit
    or lower slit in double-slit1, and the interference pattern disappears
    on screen1 to the left of the photon source.


    Because momentum is conserved, whenever one photon passes through the
    upper slit in double-slit1 (situated to the left of the source), the
    other photon must pass through the lower slit in double-slit2 (situated
    to the right of the source), as shown in Figure 2. And whenever one
    photon passes through the lower slit in double-slit1, the other photon
    will pass through the upper slit in double-slit2. Thus the
    interference pattern will also disappear on screen2 to the right of the
    source, whenever a measurement device is placed in front of the upper
    slit in double slit1 to the left of the source.


    Thus the placement of the detector in front of double slit1 to the
    left of the photon source affects the interference pattern on screen2
    to the right of the source.


    Because d1 and d2 can be changed without affecting the basic physics,
    a situation in which d1 is very, very large with d2 just a little bigger (d1 ~ d2) is conceivable. In such a scenario, by
    selectively placing a measurement device in front of double slit1 and
    removing it at a controlled interval, the interference pattern at
    screen2 will be created and destroyed at the same controlled interval,
    thereby sending a signal.

    As d1 becomes greater and greater as
    compared to d2, the signal can be sent faster and faster, transcending
    the velocity of light and approaching instantaneous.


    There could be many practical physical embodiments of such a device or apparatus for sending signals faster than the speed of light.


    One preferred embodiment would be a central photon source, and fiber
    optics run to two distant locations on either side of the photon
    source. A double slit or other interference apparatus would be
    employed at each of the two distant locations. A removable measurement
    device would be located at one or both locations, and its use or
    none-use in the setup could instantaneously affect the interference
    pattern at the other location.

    45Revolver: Method and Apparatus for Transmitting Signals Faster than
    the Speed of Light

    Feel free to email me for the paper and the figures:
    REVOLVER45@gmail.com
     
    Last edited: Jan 17, 2006
  2. jcsd
  3. Jan 17, 2006 #2

    JesseM

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    I'm not sure, but my guess would be that no interference pattern is ever seen in the total pattern of photons on the screen in such a setup, even if no measurement is made of which slit each one through; instead, the interference pattern would only be seen in the some sort of coincidence-counting, like if you only looked at the subset of photons hitting the screen on the right side that are paired to photons that hit the bottom portion of the left screen, or something along those lines. My guess here is based on an analogy with the delayed choice quantum eraser experiment which is discussed on this thread.
     
  4. Jan 17, 2006 #3
    Thanks Jesse,

    It seems strange to me that no interference pattern would ever be seen, as if a photon passes through both slits, it must interfere with itself.

    If we pictured millions or billions of photons an interference pattern would emerge.

    Or then how could a photon pass through both slits and not interfere with itself?
     
  5. Jan 17, 2006 #4

    JesseM

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    Well, look over the delayed choice quantum eraser experiment, which is also discussed on this thread. In this experiment, you have an entangled pair of photons, one labeled the "signal photon" which ends up at detector D0 (which can also be replaced with a screen as in the double-slit experiment), another labeled the "idler photon" which ends up at either D1, D2, D3, or D4. If it ends up at D3 or D4, then you know which location (analogous to the slits) the pair of photons came from, like in the double-slit experiment where you measure which slit the photons go through; if it ends up at D1 or D2, then the which-path information is lost, like in the double-slit experiment where you don't measure which slit it went through. If you look only at the subset of signal photons whose idlers end up at D3, you don't see an interference pattern, and likewise with D4. On the other hand, if you look at the subset of signal photons whose idlers end up at D1, you do see an interference pattern, and likewise with D2, so in a sense you could say the photon has "interfered with itself", as you say. But what's interesting is that the peaks of the D1 interference pattern line up with the valleys of the D2 interference pattern, so if you look at the sum of the D1 and D2 interference patterns (the subset of signal photons whose idlers ended up at either D1 or D2), you get a pattern that shows no interference. Again, look at that earlier thread I linked to above and the paper I linked to in my post there, which includes a diagram of the setup and a graph of the various signal photon patterns, showing how the peaks of the D0/D1 interference pattern line up with the valleys of the D0/D2 interference pattern.

    So like I said, I would guess that something similar happens in the setup you describe--if you look at the proper subsets of photons going to the left screen which are paired with photons going to the right screen, you would get an interference pattern, but when you summed all the possible interference patterns based on such subsets, the peaks of some would line up with the valleys of others in such a way that the total pattern shows no interference. That's just a guess since I don't know how to explicitly calculate the correct QM prediction in this setup, but I can't see any other way that FTL signalling (or even backwards-in-time signalling!) could be avoided here.
     
    Last edited: Jan 17, 2006
  6. Jan 17, 2006 #5
    Thanks Jesse,

    I looked over the link and the paper.

    If there is never any interference pattern upon the screens in the setup I describe, then the respective photons to the right and left of the source must not be passing through both slits in the double slits.

    Hence, even without being measured, the photons are behaving like particles, with definitive positions and momenta.

    But if the photons are behaving as waves, then an interference pattern must be produced.

    Thanks.
     
  7. Jan 17, 2006 #6

    JesseM

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    But what if there is interference when considering various subsets of photons in your setup--like considering the subset of all photons hitting the right screen that are paired with photons hitting the bottom half of the left screen--but when all these patterns are added together, the result is a noninterference pattern?

    Perhaps it would be better to talk about this issue in terms of the delayed choice quantum eraser experiment, where it's clearer what subsets we're considering. If we look at the total pattern of signal photons on the screen and see no interference, would you say this means the signal photon/idler photon pairs are not coming from both radioactive atoms A and B (which are analogous to the slits)? If that's what you would say, how do you explain the fact that when we consider only the subset of signal photons whose idlers end up at D1, we do see an interference pattern? Does this mean that the photons in this subset are coming from both atoms?

    To make this problem sharper, suppose we replace the beam-splitters BSA and BSB in the fig. 1 of that paper with mirrors, so all the idlers end up at D1 and D2. Again, if you look at the subset of signal photons whose idlers ended up at D1, you see an interference pattern; and if you look at the subset of photons whose idlers ended up D2, you see an interference patter; and every photon falls into one subset or the other. So does this mean every photon did come from both radioactive atoms? But then if you look at the total pattern of signal photons (the sum of photons from the first subset with photons from the second), you see a non-interference pattern. Does this mean every photon did not come from both radioactive atoms?

    It seems to me the problem is that your terminology is fuzzy--I don't really see what it means to say that a given photon did or didn't go through both slits/come from both atoms, when a single photon can be viewed both as a member of a subset that does show interference, and simultaneously as a member of a larger subset which does not.
     
  8. Jan 17, 2006 #7
    I guess the basic question is this:

    Suppose we have a beam of two interacting spin 1/2 photons.

    The beam of photons separates, with each of the two interacting photons traveling in opposite directions.

    If in each direction there exists a double slit setup, will an interfence pattern be created on a screen beyond the double slit?
     
  9. Jan 17, 2006 #8

    JesseM

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    Will the total pattern of all photons hitting the screen create an interference pattern? I think the answer is no, but I also think that certain well-defined subsets of the photons hitting the screen will create an interference pattern.

    Did you follow the details of the delayed choice quantum eraser setup well enough to be able to understand the questions I was asking in my previous post? If not, I can try to explain it further; if so, it would be helpful if you would address them.
     
  10. Jan 17, 2006 #9
    Yes--I followed your argument and will address it in a bit.

    But first I would like to remain focused on my apparatus.

    Consider a beam of photons on either side of the apparatus I describe.

    If the beam is incident upon a double slit, how could it not create an interference pattern upon a screen just beyond the double slit?

    What could possibly cause a beam of photons to not create an interference pattern?

    Thanks!
     
  11. Jan 17, 2006 #10

    JesseM

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    If I'm right that there would be no interference in the total pattern of photons, presumably the "cause" would be that photons which are members of entangled pairs do not behave in quite the same way as photons which are not, in the context of the double-slit experiment. After all, there is some possibility that by performing the right measurement on the other member of the pair, you can determine which slit the first photon went through, even without performing measurements at either of the two slits the first photon could have passed through. If this is correct, then you should be able to show that this is the case using the rules of quantum mechanics, so the ultimate "cause" is just that that's how the laws of quantum mechanics say the photon should behave, trying to translate these mathematical laws into some kind of intuitive verbal explanation may not always be possible.
     
  12. Jan 18, 2006 #11
    Would this then mean that photons which are members of entangled pairs show no interference pattern? And then would this mean that if a photon was once a member of an entagled pair, it could never again behave live a wave and interfere with itself?

    Suppose we consistently measured one of the entangled photons, thereby liberating the other photon from the entangled state. Woul the liberated photons be capable of behaving like photons and creating an interference pattern after passing hrough a double slit? Because this is another manner in which signals may be sent faster than the speed of light.
     
  13. Jan 18, 2006 #12

    ZapperZ

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    Er... suppose we DON'T have a beam of interacting spin 1/2 photons!

    Zz.
     
  14. Jan 18, 2006 #13

    ZapperZ

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    Entangled photons do interfere, but not within the entangled unit. It has been shown that entangled photons beat the diffraction limit[1,2], as it should if the entangled glob cannot be considered as separable (mathematically) and thus have a higher energy (freq) as an entity.

    Zz.

    [1] P. Walther et al., Nature v.429, p.158 (2004).
    [2] M.W. Mitchell et al., Nature v.429, p.161 (2004).
     
  15. Jan 18, 2006 #14
    Suppose we consistently measured one of the entangled photons, thereby liberating the other photon from the entangled state. Woudl the liberated photons be capable of behaving like photons and creating an interference pattern after passing hrough a double slit? If so, then signals may be sent faster than the speed of light.

    If one can intentionally alter an interference pattern from afar at velocities faster than light, then an apparatus may be designed for faster-than-light communication.
     
  16. Jan 18, 2006 #15

    JesseM

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    That's not how it works. The other photon will continue to behave in an entangled way until it is measured; if you compare the first measurement of photon A with the first measurement of photon B you should find the correlations that are characteristic of entanglement, even if photon A was measured long before photon B. Subsequent measurements of particles that were previously entangled would no longer show entanglement though, it's only the first measurement of each that counts.
     
    Last edited: Jan 18, 2006
  17. Jan 24, 2006 #16
    The interference pattern disappears on screen1 because you've, in effect, closed one of the openings in double-slit1.
    The side that has both slits open will show an interference pattern. The side that has one slit closed will not show an interference pattern.
    No. Closing one of double slit1's openings will not affect the raw data interference pattern produced by double slit2. Double slit2 produces interference banding (after about 60 to 70k detections) because both its slits are unobstructed. Double slit1, with an obstructed opening, will not.
     
  18. Jan 24, 2006 #17

    JesseM

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    Are you sure about that? By conservation of momentum, if you know which slit one photon went through, doesn't that mean you know which slit its entangled twin went through? The pattern you describe isn't how it works in the delayed choice quantum eraser--there instead of two slits a particle can go through you have two atoms which periodically emit pairs of photons, one labeled the "signal" photon which goes towards a screen similar to the double-slit experiment, and the other labeled the "idler" photon which goes through a system of beam-splitters and mirrors arranged so that, depending on which detector the idler ends up at, you either recover the "which-path" information about which atom it came from (and thus which atom the corresponding signal photon came from), or the which-path information is "erased". But in neither case do you see any interference in the total pattern of signal photons on the screen, despite the fact that you had no measuring device to detect which of the two atoms a given signal photon came from--you only see interference when you do coincidence-counting between the subset of idler photons that ended up at a detector where there which-path information was erased and the corresponding subset of signal photons. So, I guessed that something similar would be true in the experiment described in this thread, where you would never see any interference pattern in the total pattern of photons on either screen, interference would only be visible if you did coincidence-counting between various subsets (like maybe the subset of all photons on one screen whose twin ended up in a certain narrow region on the other screen).
     
  19. Jan 24, 2006 #18
    I'm not sure about anything yet. :smile: But, afaict, Dr. RMC wasn't describing a delayed choice quantum eraser setup. In the OP setup there was just doubleslit1 with a detector obstructing one of the slits, and doubleslit2 with both slits open. The raw data on the detecting screen1 will show no interference because the light going through the slit where the detector is placed next to doubleslit1 is absorbed by the detector and can't interfere with the light transmitted by the other, open, slit. On the other side, neither slit of doubleslit2 is obstructed, so you eventually get an interference pattern on screen2.

    If you pair the photons via coincidence detection and then select out the portion of side 2's data corresponding to what is detected at side 1's screen slit detector, then there will be no interference pattern on side 2. I don't know if this can be done in real time or not. If not, and if the data output is irreversible (say, a photographic plate as opposed to a video monitor), then what you will see is an interference pattern on side 2, but what you will statistically calculate will be a clumping corresponding to side 1's output.

    Or, you can erase the which way info on side 1 (in effect, remove the detector obstruction from the closed slit --- recreating, in effect, the original situation with both slits open in doubleslit1) by coincidence matching with side 2 and reintroducing the missing statistical info to side 1 to get an interference pattern (even though the raw data output might not actually show an interference pattern on screen1).

    It's not which way info, per se, that determines whether you get an interference pattern or not --- it's that in order to generate which way info you have to, in effect, close one of the slits in the double slit device. And, to erase which way info you have to, in effect, reopen the closed slit.

    I've noted the thread on Scully's paper you referenced. It's on my list of things to read. Also, I found this:
    http://www.bottomlayer.com/bottom/kim-scully/kim-scully-web.htm

    ... which looks like it might be a good explanation of it.

    Any corrections wrt what I've written are appreciated.
     
    Last edited: Jan 24, 2006
  20. Jan 24, 2006 #19

    JesseM

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    I know, but it seemed to me like there was some kind of analogy there--in both setups, on one side you have a photon coming from one of two locations with no measuring device to tell you which one it came from (the photon going to the right in Dr. RMC's setup vs. the signal photon coming from one of two atoms in the DCQE), but on the other side you have its twin where, depending on what kind of measurement you make on the twin, you may be able to tell where both photons came from (the photon going to the left in Dr. RMC's setup, where you can put in a detector to tell which slit it went through and then deduce which slit the other photon went through by conservation of momentum vs. the idler photon whose which-path information can be discovered if it goes to certain detectors in the DCQE). In the DCQE there is no interference in the total pattern of signal photons no matter what measurement is made of the idler, so I thought something similar would probably be true of the setup Dr. RMC describes. After all, suppose you did see interference in the total pattern of photons on the right side, but then you had a detector on the left side so you always knew which slit each photon on the left went through; by conservation of momentum you should then know which slit each photon on the right went through, so if you see interference in the photons on the right doesn't that contradict complementarity?
    But that's what I'm saying, I don't think you can assume that you will get interference when both slits are open but the photons are members of entangled pairs. Again, if you know which slit each photon on screen1 went through, that would seem to tell you which slit each photon on screen2 went through (despite the fact that both slits to screen2 were open with no detectors near them), since conservation of momentum should hold for members of entangled pairs, as I understand it. Again, there's the analogy with the DCQE where the signal photon can come from either of the two atoms (which are analogous to the slits) and so looking at the signal photons alone it might seem like you should get interference in their total pattern, but in fact you don't, you only get it in coincidence-counting between idlers whose which-path information was erased and the corresponding signal photons.
    But what if the detector on side 1 was on all the time, so you know which slit every photon on that side went through? This should also tell you which slit every photon on side 2 went through, but whether you see interference in the total pattern of photons on side 2 can't depend on whether the detector is on or off on side 1, or this would lead to the possibility of FTL or backwards-in-time signalling just as Dr. RMC suggested.
    But isn't that part of the basic idea of complementarity, that an experiment can reveal particle-like or wavelike behavior but not both at the same time? If there could be a double-slit type experiment where you see an interference pattern on the screen but you also know which slit each particle went through, this would seem to be a violation of that idea. But I only have an intuitive understanding of what "complementarity" means so I'm not sure about this (I'm not even sure if 'complementarity' is even an idea that's ever been formalized, I've seen some debates between professional physicists about issues involving complementarity where neither ever referred to any formal definition of the principle to settle the argument).
    You don't necessarily have to close it--if you do the double-slit experiment with electrons or some other particle that can be detected without being absorbed (I don't think this is possible for photons although I'm not sure), then you can just have a detector at one of the slits that detects by scattering some other particle like a photon off the electron, still allowing the electron to go through that slit.
     
  21. Jan 26, 2006 #20
    Afaik, with both slits open, there's no way to know if a single-photon detection was produced by light that went through both slits or only one. What's known is only that both slits were open and an interference pattern eventually emerged.
    If you put a detector behind one of the slits (between the double-slit device and the screen), then you could think of this as both slits still being open, in which case, after a single-photon detection at the slit or at the screen there's still no way to know if all of the light incident on the double-slit device went through both slits or only one.
    In the setup Dr. RMC describes, without pairing the photons via coincidence processing, and then doing some additional data processing, then what would be expected is that screen1 will not show an interference pattern and screen2 will show an interference pattern.
    If, after coincidence matching, a logic pulse is sent from the slit detector on the left side via circuitry that then blocks the transmission of its twin to the the right side screen2 detector, then no interference pattern will emerge on screen2.

    I have to read up on complementarity (I forget exactly how Bohm presented it in his textbook) --- but isn't it just part of Bohr's qualitative (Copenhagen) interpretation? If so, then violating it wouldn't diminish the validity of the mathematical formulation of QM --- which, afaik, predicts an interference pattern for screen2 of Dr. RMC's setup and no interference pattern for screen1.
    The fact that paired photons are entangled just allows some processing that wouldn't otherwise be allowed. Without any additional processing, and just transmitting through an unobstructed double-slit device, then you'll get an interference pattern on the screen. Afaik, there's no reason to assume that the components of an entangled pair are in any way affecting each other as they move apart.
    The photon isn't what went through one slit, or the other, or both. Afaik, nobody knows what's happening at that level. The photon is the detection attribute. If the single-photon slit detector on side 1 registers a detection, then nothing further is known about the qualitative behavior of the source-emitted light or the slit(s)-transmitted light (did something go through only one slit or both?) corresponding to that detection other than that the single-photon slit detector on side 1 registered a detection.

    So, the results on side 1 don't really give qualitative which-way info. The only thing that can be said is that if the slit detector registers then for sure something went through the slit where the detector is, and if screen1 registers then for sure something went through the unobstructed slit. On side two, where the interference pattern emerges, everything that's known about light suggests that it's reasonable to assume that the light incident on the double-slit device corresponding to a single-photon detection at screen2 went through both slits. But what is actually happening at that level is still a mystery.
    It doesn't. Unless you do some signal or data processing, what's done on one side of the setup won't affect what happens on the other side.
    With both slits of the double-slit device open you get a wave-like distribution on the screen that's characteristic of two waves transmitted by and spreading omnidirectionally out from the two parallel openings and interfering.

    With only one slit of the double-slit device open you get a wave-like distribution on the screen that's characteristic of one wave transmitted by and spreading omnidirectionally out from a single opening.

    In both cases, the wave-like detection patterns are composed of particle-like single photon detections.
     
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