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Superliminal communication through quantum entanglement

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  • Superliminal communication through quantum entanglement

    Brian Greene, the John Cusack of String Theory, got me interested in quantum after I read his latest book, Fabric of the Cosmos. He talks about how entanglement can't be used for faster than light communication, but after seeing the delayed choice experiment I have to wonder why. So, unless you're interested in quantum, this will probably seem a little fucked.

    Here's the basic setup: (see this diagram for a better idea) we have A and C seperated by a given distance and B at their midpoint. B contains a special laser which spits out individual photons at a fixed rate. This laser is run through a beam splitter (BS), both outputs of which are fed into down converters (DC) which generate entangled photons. It's basically two copies of Aspect's experiment to prove ESR-like "spooky" action being fed by a beam splitter, so it's being combined with a modified form of the double slit experiment to elicit the "delayed choice" effect through entanglement.

    The pair of entangled photons emerging from the DCs travel through space, arriving at A and C simultaneously. C has two mirrors/prisms which direct the beams across each other onto a viewing screen. A has a "which path detector" (WPD) which can be selectively toggled.

    When A's WPD is off, the probability waves emerging from both paths of the beam splitter are uncollapsed. Consequently, they will interfere with each other when their paths cross as they are projected onto C's screen. However, by switching on the WPD, A can collapse the probability waves at C through the "delayed choice" effect, eliciting particle-like behavior from the entangled photons and destroying the interference pattern on C's side.

    So while you have to wait for the photon stream to reach A and C initially, A should, in theory, be able to communicate a message of "wave" or "particle" to C instantaneously, which should be exhibited by either the presence or absense of an interference pattern on C's screen respectively.

    My first question is did anyone actually read that? If you answered yes, then my second question is does anyone care? Finally, if you answered yes to that question, my third question would be... does this actually work? My guess is... no
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  • #2
    Wireless communication using quantum engalleument to ensure privacy

    Certainly there has been much research both in Key generation using quantum uncertainty and also long distance communication. However these techniques do not provide for Superluminal (faster than light) communication, only secure communication

    Some good papers for the quantum comms can be found at


    QuComm Presentation

    QuComm Report
    And more recent study from the same group, across Vienna. Free space Optics Study

    Comment


    • #3
      Holy rusted metal batman!!! A 3 post user that's not an asshat!!! Hope this is a tread!

      Thanks for the great reads btw!
      "Never Underestimate the Power of Stupid People in Large Groups"

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      • #4
        Originally posted by hackajar
        Holy rusted metal batman!!! A 3 post user that's not an asshat!!! Hope this is a tread!
        This user *can't* be real. I suspect it's really someone with over 1,000 posts who wants an "alternate" identity to post under... yeah.. yeah, that must be it...
        “Bigamy is having one wife too many. Monogamy is the same.”

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        • #5
          Originally posted by evad123
          Certainly there has been much research both in Key generation using quantum uncertainty and also long distance communication.
          The Aspect experiment, demonstrating EPR "spooky" action at a distance, also proved to be a cryptographically random number source which could facilitate streaming OTP. When spins of the entangled particles are measured simultaneously, they are identical, and have a perfect 50/50 random variation between clockwise and counterclockwise.

          However these techniques do not provide for Superluminal (faster than light) communication, only secure communication
          The question is why... the method I've detailed here allows you to "say" either 'wave' (by choosing not to activate the WPD) or 'particle' (by activating it) instantaneously over any distance the photons have traversed. I'm not saying it should work, but if it doesn't I'd certainly like an explanation why...
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          • #6
            Slightly more explanation from the WWW

            bascule, I was looking around last night at some of the litriture regarding quantum entalglement and in doing so came across this page, which specificly looks at the issue you mention, Hope it helps EPR Paradox ,

            And the short article on the Aspect EPR experiment

            EPR Aspect



            Dave
            Last edited by evad123; May 20, 2005, 01:06.

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            • #7
              Oh right I get ya now,

              The No Cloning theorem does not come into force because the information is not stored within the velocity and phase of the Qbit but rather as a second order effect, i.e. it resolves to wave or particle as its entangled partner does so.

              From my reading of the background material related to delayed choice experiments, the reason most frequency pointed to as to why the communications channel is not classical in this case is that the wave function is susceptible to spontaneously collapsing, thus although it will definitely resolve if the sender acts , the receiver has no means of deciding if this was due to the sender or random chance, thus no usefull information can be transfered.

              There's lots on the web about this lot , but plenty of disourse both ways. I'm sure that there must be ways of doing this to transfer informaiton by using lots of these setups in parralel. Thus only if every single one colapsed simultainsly would the sender have sent a message, I'm sure there's a physisist out their who can say why not tho.
              Last edited by evad123; May 20, 2005, 08:05.

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              • #8
                Originally posted by evad123
                From my reading of the background material related to delayed choice experiments, the reason most frequency pointed to as to why the communications channel is not classical in this case is that the wave function is susceptible to spontaneously collapsing, thus although it will definitely resolve if the sender acts , the receiver has no means of deciding if this was due to the sender or random chance, thus no usefull information can be transfered.
                The probability wave collapses when particle-like behavior is elicited. This would occur sporadically if the photons in the entangled beam headed for A collided with another particle.

                However, this setup is sending out individual photons at regular intervals, then waiting for impacts at C. You would then have to wait for thousands or millions of photons to arrive at C. The wave function will very likely collapse for many of these photons, but that doesn't mean the interference pattern still wouldn't be visible.

                For example, in the delayed choice quantum eraser experiment, the setup ensures that "which path" information is erased 50% of the time. The photons trace out a pattern that contains both the interference pattern and the non-interfering collapsed pattern of individual photons exiting either of the paths. It looks something like this:



                Compare that to when the probability wave is collapsed 100% of the time and the photons must essentially 'pick a path' precluding any interference:



                The difference between the two is quite discernable, even when half the photons you send have the "wrong message" encoded. The redundancy comes in how many photons you have to send to transmit a single "bit" as the message is only discernable through statistical analysis of a rather large data set.
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                [ redacted ]

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                • #9
                  noise or signal

                  I think this discussion thread looks at precisely this issue, however for me the explanations given are nasty (they imply its impossible because QM says it is) and seem to defy logic but there you are enjoy Faster than light comms
                  Seti Quantum Comms

                  Comment


                  • #10
                    Twt

                    Hello.

                    How about something along the lines of a Travelling Wave Tube, but in the Optical range?
                    As the theory goes, a black hole sucks everything in, including light.
                    The only thing that can escape the extreme force of gravity seems to be some form of X-rays.
                    So, the question is, what is the exact speed of light at all ends of the spectrum.
                    Is red slower then blue?
                    Remember the doppler shift?
                    We can bump up the color spectrum, this is how most green laser-pointers work.
                    A lot of questions, I know.

                    Comment


                    • #11
                      Originally posted by Cowthief
                      How about something along the lines of a Travelling Wave Tube, but in the Optical range?
                      As the theory goes, a black hole sucks everything in, including light.
                      The only thing that can escape the extreme force of gravity seems to be some form of X-rays.
                      What escapes is Hawking Radiation, which is composed primarily of photons and neutrinos.

                      So, the question is, what is the exact speed of light at all ends of the spectrum.
                      c

                      Is red slower then blue?
                      No

                      Remember the doppler shift?
                      We can bump up the color spectrum, this is how most green laser-pointers work.
                      A lot of questions, I know.
                      Doppler shift alters the frequency of the light, not its velocity. Light always travels c.
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                      [ redacted ]

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                      • #12
                        Originally posted by bascule
                        Light always travels c.
                        *Always* ?
                        ]:>

                        If so, is "c" a single value or are you going to go with a "by definition" statement?
                        (My reply could be considered trolling, depending upon your answer.)

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                        • #13
                          Originally posted by TheCotMan
                          *Always* ?
                          ]:>

                          If so, is "c" a single value or are you going to go with a "by definition" statement?
                          (My reply could be considered trolling, depending upon your answer.)
                          The value of c may change with time (evenly across the entire universe) but nothing else. Neither the frequency of the photon, where it is, or what it's passing through will affect it. When a photon is a photon, it's travelling c.
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                          • #14
                            "C" the great constant


                            Bascule: I can best think of C as being relative to the electron. That means that the total speed of the photon is C plus the speed of the electron. Would this be correct?
                            "It is difficult not to wonder whether that combination of elements which produces a machine for labor does not create also a soul of sorts, a dull resentful metallic will, which can rebel at times". Pearl S. Buck

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                            • #15
                              Originally posted by bascule
                              The value of c may change with time (evenly across the entire universe) but nothing else. Neither the frequency of the photon, where it is, or what it's passing through will affect it. When a photon is a photon, it's travelling c.
                              Ah. You chose, "by definition."

                              "c" is the speed of light. A photon is light. therefore the speed of any photon is always c, no matter what material it is passing through.

                              When you compute the value of "c" as a decimal value for a specific but well selected photon, can that computed decimal value of "c" be different from other photons that may be traveling through other medium? If so, by how much?

                              Is the speed of light constant?

                              What is the decimal value of c?

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