Chinese Satellite Achieves Quantum Entanglement Distance Record

Discussion in 'Physics & Math' started by danshawen, Jun 16, 2017.

  1. danshawen Valued Senior Member

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    http://www.latimes.com/science/sciencenow/la-sci-sn-entangled-photons-china-20170615-htmlstory.html

    A Chinese LEO (Low Earth Orbit) satellite named Micius after a 5th century Chinese scientist has achieved a new entanglement telecommunication distance record of about 1,500 miles.

    A low bit rate channel for the entanglement test was established by means of an onboard beam splitter which targeted a pair of Earth stations separated by 1,500 miles.

    Applications for the system include quantum cryptography.

    “This is the first time you have a quantum channel between a satellite and the ground that you can actually use,” said Norbert Lütkenhaus, a professor at the Institute for Quantum Computing at the University of Waterloo in Canada who was not involved in the new work. “People have been talking about doing it for many, many years, but these guys actually did it.”

    The experiment highlights some of the characteristics of quantum entanglement communications that has been previously discussed in these forums. The entanglement communication achieved is as secure as communication can possibly get. Only two spot beam identified targets can make use of the entanglement for the purpose of instant telecommunication. Some considerable effort must be expended in correlating the admittedly low bit rate communication, not unlike Forward Error Correction techniques already in heavy use for most satellite telecom applications that are not entangled.
     
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  3. origin Trump is the best argument against a democracy. Valued Senior Member

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    It does not appear to me that anyone was talking about instant communication.
     
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  5. someguy1 Registered Senior Member

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    That is really cool. Amazing that we can do experiments like that. My understanding is that it would violate physics to propagate a signal faster than lightspeed, so using entanglement for instantaneous data transmission is still not possible without another revolution in physics. Is my understanding correct? The quote seems to indicate some sort of information transfer is taking place but I don't understand how that could be possible.

    ps -- Here is a much more technically detailed article. I'm still working through it. It's very interesting. The guy behind the experiment has been pushing for it and planning it since 2003. https://www.scientificamerican.com/...ance-rdquo-record-preps-for-quantum-internet/

    pps -- Some interesting politics here too.

    But on the other hand ...

     
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  7. danshawen Valued Senior Member

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    You'd need to go back and read carefully the experiments that preceeded it (which I did), and also what they were proposing to do, which is this satellite telecom experiment.

    I worked in satellite telecom / Intelsat R&D for 22 years at the former Comsat Laboratories. I worked with world renowned satellite engineers, and many of those were Chinese American, and a few others from China, on state of the art Forward Error Correction coding projects that was the first of its kind.

    If you are believe this is beyond what Chinese engineering is capable of doing technologically because you think their science is substandard in some way, I can assure you from personal experience of working closely with them, you would be wrong.

    Give Bell's theorem as an excuse if you wish. This is a first, and I tend to believe they have been successful if they say they have.
     
  8. someguy1 Registered Senior Member

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    Where did that come from? Nobody said or implied any such thing.

    My own very humble understanding of physics is that you can't use the entangled pairs like a telegraph to transmit streams of data faster than light. Known physics flat out disallows that. So I personally would be curious to know exactly what is being communicated via this technology and how people think this could ultimately be developed into some kind of means of communication.

    ps -- Another thing I'm curious about is when I've got a photon detector sitting here, and it detects a photon, how do I know I've got the right one? How do they pick out one particular photon from all the photons that must be hitting it constantly? How do they go, Oh, this is the paired one we care about!
     
    Last edited: Jun 16, 2017
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  9. exchemist Valued Senior Member

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    I share your scepticism and would second Origin's observation that the article in question nowhere refers to "instant communication", only to a new potential technique for encryption.
     
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  10. Write4U Valued Senior Member

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    I am way out of my depth here, but the qualification of "low bit rate" seems to imply that only a small number of entangled pairs were used or perhaps necessary?

    How many entangled pairs would be needed in say, an encrypted binary coding system?

    Comes to mind something like ; left spin = 0 , right spin = 1, or short and long duration between spin reversal, as in the Morse code; . . . _ _ _ . . . ?

    Just a musing.
     
    Last edited: Jun 16, 2017
  11. danshawen Valued Senior Member

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    The prejudice against Chinese science is not entirely as strange as it sounds. Their peer review culture is a little different, but it does work.

    At one of the Earth stations, the detection of an entangled photon or group of photons instantly flips the spins of the ones being received at the other ground based station 1500 miles distant. The further away the stations, the easier it is to detect delays and verify that they are faster than light.
     
  12. Write4U Valued Senior Member

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    I have heard that an entangled pair do not actually "communicate" via a wave function (which would be restricted by "c"), but remain a quantum entangled singlet regardless of distance.

    Some form of superluminal virtual quantum mirroring function, always maintaining a zero state quantum value between the pair?

    This seems so counter-intuitive, that it is difficult to imagine, unless the pair has a (near) infinitely long virtual connection between them and the entangled singlet is never separated at all in a timeless dimension. (Bohm's Wholeness?)

    I can't even form a metaphoric imagine, even in the most abstract terms, which bugs me to no end.
     
  13. Nacho Registered Senior Member

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    It looks to me like they are just saying the quantum connection is used just for SECURE communications, not FTL communications. The entangled pairs are used to make sure no one is eavesdropping in the communications channel. If they were, they would in effect be taking a measurement on one of the pair of particles, and that would alter the message being sent, and it would be detectable by the senders.

    Charles Bennett (of IBM) did some of the ground work on this, quantum cryptography, years & years ago. I remember reading about it in Scientific American:

    https://en.wikipedia.org/wiki/Charles_H._Bennett_(computer_scientist)

    Nothing is FTL, unless somebody has something to add that I didn't see.
     
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  14. danshawen Valued Senior Member

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    That actually makes a lot of sense, and this is the first time I've heard the term "singlet" used in that context. I would agree. Thank you!
     
  15. exchemist Valued Senior Member

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    What do you think "singlet" means in this context?
     
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  16. danshawen Valued Senior Member

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    The idea that nothing, including quantum entanglement, happens faster than light can be shown to be the result of Minkowski's misconceptions about:

    1) what simultanaeity actually means (it is a different story for entanglement, and possibly without exceeding the speed of light), and

    2) a division by zero occasioned by equivocating an instant of time with a velocity or an interval of time. This effects a divide by zero because the speed of light is not the basis of time itself, which is exactly what Minkowski's proportional math erroneously assumed. Proportional math stops making sense whenever you set up a proportion that divides by zero, as is exactly the case whenever one assumes the speed of light is proportional to the speed of entanglement. It most definitely is not, and this is not pseudoscience. I've put my finger directly on his mistake, and there is no question that it is a really bad one.
     
  17. danshawen Valued Senior Member

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    Spin zero in the context of a pair of entangled photons means that if one photon is left hand circularly polarized, the other will be right handed. Total quantum spin = zero, for as long as they remain entangled.

    Of course, you could generate photons from particles that are not entangled, and in that case, there is no correlation at all between observing one and the state of the other.

    I really don't understand the amount of skepticism about this. Einstein believed it worked; said it was spooky. This does not mean he believed in ghosts, or anything like them.

    It is a direct consequence of the invariant speed of light itself being relative to something. The rest frame has to be invariant too, and a consequence of this is entanglement.
     
    Last edited: Jun 16, 2017
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  18. Write4U Valued Senior Member

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    From wiki;
     
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  19. danshawen Valued Senior Member

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    spdf in spectroscopy as well, yes.
     
  20. Nacho Registered Senior Member

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    Exactly what is a "speed of entanglement"? I think I know what you are trying to say, but I question if there is any such scientific definition or truly ANY accepted phrase. Especially since no one has discovered if any information is being transferred when the entanglement is broken. I think division by zero is non-sense (most would agree I think), and the phrase "speed of entanglement" is non-sense too.
     
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  21. QuarkHead Remedial Math Student Valued Senior Member

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    It is far from clear what you mean by "equivocating" in this context. Care to explain?
    Minkowski never stated that the speed of light is the basis of time. All he did was point out that \(ct\) should be considered on an equal footing as the other 3 spatial coordinates.

    This does not involve division be zero
    There is no mistake, certainly not a division by zero
     
  22. arfa brane call me arf Valued Senior Member

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    There is no instant telecommunication. Why do you still think this despite not having posted any evidence? (because there is no evidence you can post).

    Those Chinese scientists would have used Bell's theorem, or rather, Bell state measurements.
    No.

    From IBM's bluemix site, once more, (where you can build quantum circuits on a real 5-qubit computer) . . .


    "Entanglement is a property of many quantum superpositions and does not have a classical analog. In an entangled state, the whole system can be described definitively, even though the parts cannot.
    Observing one of two entangled qubits causes it to behave randomly, but tells the observer exactly how the other qubit would act if observed in a similar manner. Entanglement involves a correlation between individually random behaviors of the two qubits, so it cannot be used to send a message.
    Some people call it “instantaneous action at a distance,” but this is a misnomer. There is no action, but rather correlation . . ."

    Note that: (1) measurement 'causes' each particle to behave randomly. How can you communicate information with random measurement outcomes? What would you suggest?

    (2) there is no action. What can this mean? What kind of communication can have no action?

    (3) at IBM's site, you can recreate the Chinese experiment, albeit over much shorter distances, and get exactly the same results . . .
     
    Last edited: Jun 16, 2017
  23. danshawen Valued Senior Member

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    http://newatlas.com/quantum-entanglement-speed-10000-faster-light/26587/

    The above link is a report from one of the first references to the speed of entanglment.

    I understand that this is not a link to Nature. Boy, do I get tired of reading about Bob, and Carol, and Ted and Alice doing entanglement experiments. Let me tell you what is really going on.

    Suppose I told you that there was such a thing as absolute time in terms of the instant of time we refer to as "now". Suppose that this instant is the same throughout a quantum field that spans the entire universe. Never mind the other properties of that quantum field for now. Just assume that absolute time exists, not in the guise of an absolute velocity like the invariant speed of light, but in an instant of time that is the same everywhere, even though after that instant, relative time dilation, gravitational time dilation, and other effects may mean literally that time proceeds at different RATES everywhere in the known universe.

    There is no such correspondence to absolute space for a universe that is not static, and that is comprised of only energy transfer events and time, but that is another story. Don't get all greek classical and Euclidean about nailing a coordinate system origin in inertialess space just yet.

    When I tell you that even the invariant speed of light must be relative to something, that something is the rest frame, which has several forms of invariance of its own for matter or antimatter, which are bound forms of energy, as opposed to linearly propagating photons, which are unbound at least until or unless they are absorbed by an electron in atomic structure.

    In that rest frame, the instant of time t=0 means the same thing "now" everywhere in the known universe. And an instant of time cannot be proportional to a velocity, even an invariant one like the speed of light in a vacuum. It follows that when entangled electrons change quantum spin states, or when entangled photons are observed pretty much amounts to the same instant of time that can either be viewed as occuring faster than it takes light to travel between them, or the other interpretation, which I find I am preferring more and more, is that entanglement spin flips occur simultaneously (for real) in pairs outside of the spacetime description of Minkowski, which really means that they actually occur IN THE INVARIANT REST FRAME, very close to the instant of time t=0.

    The speed of light is not the fundamental basis of time. The rest frame is. The frame in which matter and antimatter persist in time is the invariant equivalent and equal of the frame that propagates at c and persistence in time for propagating unbound energy means something else entirely. But entanglement measns exactly the same in both of the uniquely invariant frames.

    If this doesn't really make sense to anyone but me, it comes as no surprise. No matter. I don't care a whit about Bell's Theorem or anything that fails to explain spooky action at a distance, because it makes perfect sense to me. Euclidean distance doesn't exist because an origin of a coordiate system does not exist in inertialess space. Light travel time exists, but it is not the "fastest" process in the universe. "Faster" or "slower" is relative too, you see? Let that insight sink in and soak for a while.

    Who else here really believes that from the "inertial frame of reference" of a photon traveling at c, time itself "stops" in any meaning of the word? It doesn't. If the photon wss right hand circularly polarized, it keeps right on spinning while it is propagating at c. The electric and magnetic fields that comprise propagating EM radiation keep right on changing. This is the opposite of time coming to a standstill. And for matter or antimatter traveling at 0.9999999... c, time doesn't really "stop" either, just because Minkowski felt the need to divide by zero or misdefine simultanaeity or time itself to show that it did. It doesn't. This is why his math only works for relative v<=c

    The instant of time we refer to as "now" need not be identically a zero length time interval either. It only needs to occur faster "slower" than light propagates in a vacuum in order for entanglement to make sense. It may not be zero length identically, but it is a fact that nothing in the universe is faster "slower" than whatever the interval of time for quantum entanglement spin flip actually is.

    Space and time are related only in that space is an artifact of time, and trying to relate the two through the speed of light is as bad an idea as dividing by zero. Remove this inconsistency and entanglement makes perfect sense, and the fact that it works instantaneously over any distance makes perfect sense.

    With apologies to exchemist. I know he is sick of reading my drivel about why these are important experiments.
     
    Last edited: Jun 17, 2017

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