• Jackson
    1.8k
    ‘Quantum Internet’ Inches Closer With Advance in Data Teleportation

    Their research, unveiled this week with a paper published in the science journal Nature, demonstrates the power of a phenomenon that Albert Einstein once deemed impossible. Quantum teleportation — what he called “spooky action at a distance” — can transfer information between locations without actually moving the physical matter that holds it.

    https://www.nytimes.com/2022/05/25/technology/quantum-internet-teleportation.html
  • Jackson
    1.8k
    "Although it cannot move objects from place to place, it can move information by taking advantage of a quantum property called “entanglement”: A change in the state of one quantum system instantaneously affects the state of another, distant one.

    “After entanglement, you can no longer describe these states individually,” Dr. Northup said. “Fundamentally, it is now one system.”
  • jgill
    2.3k
    There's something fishy about entanglement. Years ago, as a kid fishing in the gulf of Mexico I would experience it often. Why did Einstein make such a big deal of it? :chin:
  • Jackson
    1.8k
    Why did Einstein make such a big deal of it?jgill

    Einstein did not like the quantum model. He still understood physics under the old deterministic model.
  • jgill
    2.3k
    Einstein did not like the quantum model. He still understood physics under the old deterministic model.Jackson

    What does that have to do with fishing?
  • Jackson
    1.8k
    What does that have to do with fishing?jgill

    I am not a good audience for your stand up routine.
  • Wayfarer
    16.3k
    Here's a story from 2017 about using entanglement to secure communications:

    a team of physicists reports that it sent eerily intertwined quantum particles from a satellite to ground stations separated by 1200 kilometers, smashing the previous world record. The result is a stepping stone to ultrasecure communication networks and, eventually, a space-based quantum internet.

    Einstein did not like the quantum model. He still understood physics under the old deterministic model.Jackson

    Einstein clung to the realist view. He absolutely believed that the Universe was just so, independently of anything the observer did. So he could never accept the uncertainty principle was anything other than a lack of knowledge about the object. 'The dependence of what is observed upon the choice of experimental arrangement made Einstein unhappy', wrote John Wheeler. 'It conflicts with the view that the universe exists "out there" independent of all acts of observation'. But Einstein's views on this question have been refuted by subsequent experimental evidence.
  • Jackson
    1.8k
    But Einstein's views on this question have been refuted by subsequent experimental evidence.Wayfarer

    Quantum mechanics is more in line with how I think. The deterministic model never made sense to me.
  • noAxioms
    1k
    "A change in the state of one quantum system instantaneously affects the state of another, distant one.Jackson
    If this is a quote from the story, it's pop nonsense.
    Entanglement doesn't mean that you do something to one end and it can be measured at the other. Information could be sent faster than light with such a mechanism, and this is what they seem to be claiming here.
    Entangled particle behavior isn't action at a distance, but only correlation of measurement at a distance.

    Einstein clung to the realist view. He absolutely believed that the Universe was just so, independently of anything the observer did.Wayfarer
    He would not have liked what Bell contributed to it all. Einstein was very much a realist (the universe in a state independent of measurement) which sort of suggests a Bohmian attitude, but Einstein also clung to locality (that effect cannot precede cause) and Bell proved that you have to choose between the two principles. I prefer the locality principle, but my preference doesn't invalidate the strict realist (counterfactual) view. Poor Einstein couldn't have his cake and eat it too, but I don't think lived long enough to know that.

    Teleportation has been demonstrated at least a decade ago, but it wasn't done faster than light. When asked if it was the same physical matter at the source and destination, they replied "does it matter?". The original object was destroyed in the process, similar to Star Trek transporter. It wasn't a cloning booth which is necessarily limited by Heisenberg.
  • Jackson
    1.8k
    Entangled particle behavior isn't action at a distance, but only correlation of measurement at a distance.noAxioms

    If you are a physicist you may prefer reading the journal article:

    Qubit teleportation between non-neighbouring nodes in a quantum network

    https://www.nature.com/articles/s41586-022-04697-y
  • Wayfarer
    16.3k
    He would not have liked what Bell contributed to it all.noAxioms

    The discomfort that I feel is associated with the fact that the observed perfect quantum correlations seem to demand something like the "genetic" hypothesis. For me, it is so reasonable to assume that the photons in those experiments carry with them programs, which have been correlated in advance, telling them how to behave. This is so rational that I think that when Einstein saw that, and the others refused to see it, he was the rational man. The other people, although history has justified them, were burying their heads in the sand. I feel that Einstein's intellectual superiority over Bohr, in this instance, was enormous; a vast gulf between the man who saw clearly what was needed, and the obscurantist. So for me, it is a pity that Einstein's idea doesn't work. The reasonable thing just doesn't work. — John Stewart Bell, quoted in Quantum Profiles, by Jeremy Bernstein

    ---------------------

    Teleportation has been demonstrated at least a decade agonoAxioms

    The article I referred to was not about teleportation but about using the principles of entanglement for secure communications.

    In their first experiment, the team sent a laser beam into a light-altering crystal on the satellite. The crystal emitted pairs of photons entangled so that their polarization states would be opposite when one was measured. The pairs were split, with photons sent to separate receiving stations in Delingha and Lijiang, 1200 kilometers apart. Both stations are in the mountains of Tibet, reducing the amount of air the fragile photons had to traverse. This week in Science, the team reports simultaneously measuring more than 1000 photon pairs. They found the photons had opposite polarizations far more often than would be expected by chance, thus confirming spooky action over a record distance (though the 2015 test over a shorter distance was more stringent).

    All that said, I'm the first to admit that I'll never understand quantum computing.
  • Agent Smith
    6.2k
    There's something fishy about entanglement. Years ago, as a kid fishing in the gulf of Mexico I would experience it often. Why did Einstein make such a big deal of it? :chin: — jgill

    Same here! Einstein's worldview didn't allow for spooky action at a distance - it just didn't gel/jibe with his other ideas, whatever they were. The likely culprit was his light speed limit postulate + causality as understood in physics (cause must precede effect); it boils down to the same thing I suppose.

    Last I checked, quantum entanglement was, for some reason, not communication-apt i.e. we can't use to transmit info. I was wrong then and so was Einstein. Too bad!
  • Jarjar
    17
    No information is sent.
  • Jarjar
    17


    Realism and non-locality are compatible. If the wave function is real, it constitutes a causal, non-local fork, causing both
  • Jarjar
    17


    Realism and non-locality are compatible. A wave function is a non-local real causal fork, correlating distant measurements.
  • noAxioms
    1k
    This is so rational that I think that when Einstein saw that, and the others refused to see it, he was the rational man. The other people, although history has justified them, were burying their heads in the sand. I feel that Einstein's intellectual superiority over Bohr, in this instance, was enormous; a vast gulf between the man who saw clearly what was needed, and the obscurantist. So for me, it is a pity that Einstein's idea doesn't work. The reasonable thing just doesn't work.
    — John Stewart Bell, quoted in Quantum Profiles, by Jeremy Bernstein
    Wayfarer
    Yes, that's the Einstein I've grown to know. When it came to putting together special relativity, several others were working on similar theories, but he was able to see what was needed and not let old biases get in the way of drawing a very unintuitive conclusion.
    The first thing you do is the simple train thought experiment which trivially (without equations even) demonstrates the Relativity of Simultaneity (RoS), which even today many people cannot accept. Lorentz was one of the others and had a significant head start on the work, but 'buried his head in the sand', attempting to get a workable theory that didn't embrace RoS.

    Teleportation has been demonstrated at least a decade ago
    — noAxioms

    The article I referred to was not about teleportation but about using the principles of entanglement for secure communications.
    That comment was an admittedly poorly placed reply to the OP which suggests that entanglement is a form of teleportation, which it isn't. The teleportation of which I speak is real, but it doesn't work faster than light.

    As for the secure communications, yes, entangled particles are used for that, although I could not describe how it works exactly without looking it up. It has nothing to do with fast messages, but it can be used to tell if the message had been seen/copied between source and destination. It sort of works like the self-destructing messages in Mission Impossible except the message isn't destroyed, but a detector says that the recipient isn't the first recipient.

    "In their first experiment, the team sent a laser beam into a light-altering crystal on the satellite. The crystal emitted pairs of photons entangled so that their polarization states would be opposite when one was measured."
    So their polarization states would be opposite when both were measured. Not sure what you're quoting, but it implies the unmeasured one has a determined state, which is demonstrably false. But the quote says how they manage to deliver an entangled pair to very different locations without having to 'mail' one of them.

    "They found the photons had opposite polarizations far more often than would be expected by chance"
    Better than random. That's all? I would have hoped for better reliability than that.

    --------------

    Einstein's worldview didn't allow for spooky action at a distance - it just didn't gel/jibe with his other ideas, whatever they were.Agent Smith
    And said spooky action has never been demonstrated, so his 'other ideas' (principle of locality, or cause before effect as you put it) is quite safe. Only a non-local interpretation like Bohmian mechanics posits said spooky action, and also the effect-before-cause that comes with it. They've demonstrated effects caused by decisions that were made years into the future. A local interpretation would deny that description of the same experiment.

    Last I checked, quantum entanglement was, for some reason, not communication-apt i.e. we can't use to transmit info. I was wrong then and so was Einstein. Too bad!
    Did Einstein ever suggest otherwise, that entanglement could be used for communication? If so, then there really would have been falsification of locality, a principle which has never been falsified. Einstein was not wrong about that one, but he hasn't been proven right either, and never will. These things are simply interpretation dependent and not provably right or wrong. If they were, they'd be actual theories, not just interpretations.
  • Jarjar
    17


    It is definitely true that a measurement on one part of system with spatially separated components doesn't influence a measurement on the other part but the outcome of the other part is fixed still. Of course you can't know what is fixed because the observer on the other side had to send that information FTL. Which is exactly which is not possible! The only thing the other observer measures is what you measure. He would know what you measured. Which is based on chance. So no useful information can be sent. Any popular shoutings that information has been teleported (and there are myriads!) is empty shouting.
  • jgill
    2.3k
    Better than random. That's all? I would have hoped for better reliability than that.noAxioms

    :up:
  • Gregory
    4.3k
    Can information go through wormholes in space?
  • Wayfarer
    16.3k
    Not sure what you're quotingnoAxioms

    https://www.science.org/content/article/china-s-quantum-satellite-achieves-spooky-action-record-distance

    ‘Better than random’ I took to mean a re-confirmation of the Bell inequality i.e. if there had been no entanglement demonstrated then results would have been random.

    And said spooky action has never been demonstrated,noAxioms

    Wait - wasn’t the Bell inequality, and its subsequent validation by Aspect and Zellinger, precisely a demonstration of that?

    These things are simply interpretation dependent and not provably right or wrong. If they were, they'd be actual theories, not just interpretations.noAxioms

    Quanta Magazine has an explainer called How Bell's Theorem Proved Spooky Action at a Distance is Real, in case there is any question about that.
  • noAxioms
    1k
    And said spooky action has never been demonstrated,
    — noAxioms

    Wait - wasn’t the Bell inequality, and its subsequent validation by Aspect and Zellinger, precisely a demonstration of that?
    Wayfarer
    By 'spooky action', I'm referring to cause and effect events being separated by a space-like manner, in other words, faster than light. If such a thing (or reverse causality) could actually be demonstrated without begging additional postulates, that would be a falsification of all local interpretations.

    Quanta Magazine has an explainer called How Bell's Theorem Proved Spooky Action at a Distance is Real, in case there is any question about that.
    It seems to be pop-science nonsense. All of relativity would crumble if locality was falsifiable.

    Some clues: "Bell demoted locality from a cherished principle to a testable hypothesis".
    Bell did no such thing. The article also seems to presume that Bell's theorem demonstrates this violation of the principle of locality, when it fact it demonstrates that (with the exception of one loophole) one of two principles must be false, the other being the principle of counterfactual definiteness.

    "correlated, even when the particles are far apart and measured nearly simultaneously". This wording suggests absolute simultaneity, evidence of a naive writer, or one simply pandering to a naive reader. I mean, when they take the two widely separated measurements, which measurement is the cause of the result (effect) of the other? Which way does the action 'go'?

    "Hidden variable theories can explain why same-axis measurements always yield opposite results without any violation of locality"
    This is opposite of what I know, that the hidden variable interpretations (Bohm in particular) are the ones that deny locality, while the local interpretations (MWI or RQM or even Copenhagen) do not require hidden variables. Once again, either the author seems uninformed, or Bohm has been spinning his view in a new way.

    The article seems very much to assume something like Bohm's interpretation since the assume the electron already has a spin along a certain axis before it is measured. But that assumption doesn't invalidate the local interpretations.

    "Let’s now assume the world is described by a local hidden variable theory, rather than quantum mechanics."
    HVT (as they're calling it) is an interpretation of QM, not a theory separate from it. QM theory doesn't describle what's going on, but rather specifies what will be measured. It is an empirical theory, while HVT is metaphysical conjecture with zero empirical predictions.

    "both labs will obtain the same result 75% of the time. This exceeds Bell’s upper bound of 67%.
    That’s the essence of Bell’s theorem: If locality holds and a measurement of one particle cannot instantly affect the outcome of another measurement far away, then the results in a certain experimental setup can be no more than 67% correlated."
    What bell actually demonstrated is that entanglement cannot be explained by classic means.
    A classic entanglement is to split a coin edge-wise. If you look at one half here and see heads, you know the other guy has the tails, but it doesn't mean any faster-than-light action took place. Quantum correlations are stronger than that and cannot be a function of classical physics. This article totally misrepresents that conclusion and begs a principle that local interpretations do not.

    I'm not claiming to be an expert on all this, but this article seems to be asserting things that Bell did not.
  • Agent Smith
    6.2k
    @noAxioms It's a bewildering labyrinth of ideas if you ask me. Merci beaucoup for the informative post; my suspicions were proven right, instantaneous communication is inconsistent with Einstein's views on causality.

    A note: Maybe entanglement isn't a causal phenomenon, you know. True one particle's state is affected by the other particle's, but this isn't a case of one causing the other but...something else.
  • Wayfarer
    16.3k
    It seems to be pop-science nonsense.noAxioms

    Sorry but I believe Quanta’s article has it right, I think you’re the one misunderstanding the issue. (My physics is rudimentary but my English comprehension is ok.)

    All of relativity would crumble if locality was falsifiable.noAxioms

    It's a challenge to realism. That's what is 'spooky' about it.

    evidence of a naive writernoAxioms

    "Ben Brubaker is a freelance science journalist whose writing has appeared in Quanta Magazine, Scientific American and The Conversation.... He has a PhD in physics from Yale University and conducted postdoctoral research at the University of Colorado, Boulder."
  • Agent Smith
    6.2k
    It's a challenge to realism.Wayfarer

    How?
  • Rocco Rosano
    36
    RE: Action at a distance is realized. Quantum computer.
    SUBTOPIC: The challenge? and Entanglement
    ※→ Agent Smith, noAxioms, et al,

    PREFACE: Establishing an attitude that accepts or denies a theory and be prepared to work with it is NOT so great a challenge.

    It's a challenge to realism. — Agent Smith

    So for me, it is a pity that Einstein's idea doesn't work. The reasonable thing just doesn't work.Wayfarer

    (COMMENT)

      ◈ My Acceptance, with respect to the realism challenge, is that "Relativity" has been tested a number of different ways, and has NOT failed a single examination over the last century. I call that track record the response in terms of "realism."

      ◈ My Acceptance, with respect to the realism challenge, is that "Quantum Mechanics (QM)" may NOT be completely right (but then what I know about QM • and the implications it has opened up • can fit in the head of a pin), but has yet to be proven wrong.

    But in both cases (1) the study of the very fast [Relativity], and (2) the study of the very small [QM], represent progress on a scale we have never seen before. And while the two do NOT currently interlock or mutually support the other (in all the critical ways), it is NOT likely that we will discard them any time soon.

    We will still teach classical mechanics - and use it in all the same critical ways that Newtonian technology has dragged us over the last 300+ years, it may very well serve us over the next 300 years. The legacy of the giants (Isaac Newton, James Maxwell, and Albert Einstein, each once members of the Royal Society) will be remembered forever. We stand on their shoulders.

    Most Respectfully,
    R
  • Wayfarer
    16.3k
    So for me, it is a pity that Einstein's idea doesn't work. The reasonable thing just doesn't work.Wayfarer

    That quote was attributed to me, but they were not my words, it was a quote from John Bell.

    Establishing an attitude that accepts or denies a theory and be prepared to work with it is NOT so great a challenge.Rocco Rosano

    That is not too far from the advice to 'shutup and calculate' - don't worry about the fact that it's weird, just use it.

    It's a challenge to realism.
    — Wayfarer

    How?
    Agent Smith

    The very short version is, non-locality means that when you measure the properties of a particle in one position, the properties of the entangled particle are also fixed by that measurement at that instant of measurement, regardless of the distance between the two. So making a measurement here creates an outcome there without any apparent means for that information to be transmitted - because it's instantaneous, then it is faster than the speed of light which is the upper limit for any actual transmission. See this entry.

    //PS// - I had questioned NoAxiom's claim that 'all relativity would crumble' if non-locality was falsifiable. As the video below explains, this is because it suggests that causal relationships seem to propogate at faster than the speed of light, so in that sense, this claim is correct.//
  • Agent Smith
    6.2k
    The very short version is, non-locality means that when you measure the properties of a particle in one position, the properties of the entangled particle are also fixed by that measurement at that instant of measurement, regardless of the distance between the two. So making a measurement here creates an outcome there without any apparent means for that information to be transmitted - because it's instantaneous, then it is faster than the speed of light which is the upper limit for any actual transmission. See this entry.Wayfarer

    Muchas gracias for the illimuinating explanation. I think I already said this before and it was probably to you that I said it to you. There's an alternative to giving up on Einstein's theory with its cosmic speed limit for physicists and that is to admit nonphysicalism of information (nothing physical can travel faster than light).
  • Wayfarer
    16.3k
    But information is not travelling anywhere. It's not as if the properties of A are being communicated to B - that B can be 'informed about' A. That's the whole problem!

    Have a look at the interview pinned to my profile page of Christian Fuchs who has originated an interpretation called Quantum Baynsianism (QBism for short, article name A Private View of Quantum Reality.) Some relevant passages:

    QBism... treats the wave function as a description of a single observer’s subjective knowledge. It resolves all of the quantum paradoxes, but at the not insignificant cost of anything we might call “reality.” Then again, maybe that’s what quantum mechanics has been trying to tell us all along — that a single objective reality is an illusion....

    Schrödinger thought that the Greeks had a kind of hold over us — they saw that the only way to make progress in thinking about the world was to talk about it without the “knowing subject” in it. QBism goes against that strain by saying that quantum mechanics is not about how the world is without us; instead it’s precisely about us in the world. The subject matter of the theory is not the world or us but us-within-the-world, the interface between the two.

    I find that highly persuasive, because it lines up so well with phenomenology, as distinct from objectivism. Objectivism is 'what you see looking out the window'. Phenomenology is 'you looking out the window'. So it includes the observing subject.

    So what is being called into question is not reality, but a mind independent reality - the purported reality that exists 'out there now', always already there that we either perceive, or not. That is what is called into question by quantum mechanics. But, he goes on to say:

    It’s said that in earlier civilizations, people didn’t quite know how to distinguish between objective and subjective. But once the idea of separating the two gained a toehold, we were told that we have to do this, and that science is about the objective. And now that it’s done, it’s hard to turn back. I think the biggest fear people have of QBism is precisely this: that it’s anthropocentric. The feeling is, we got over that with Copernicus, and this has got to be a step backwards. But I think if we really want a universe that’s rife with possibility with no ultimate limits on it, this is exactly where you’ve got to go.

    So again, what is being called into question is scientific realism, but in a very specific sense, one which I think is peculiar to what you could call the early modern or modern period.
  • T Clark
    9.4k
    By 'spooky action', I'm referring to cause and effect events being separated by a space-like manner, in other words, faster than light. If such a thing (or reverse causality) could actually be demonstrated without begging additional postulates, that would be a falsification of all local interpretations.noAxioms

    This is the question I've been wanting to ask - Did the action at a distance take place at a rate faster than the speed of light? If not what's the big deal. It is my understanding that data transfer at a speed greater than light is believed not to be possible, even given quantum entanglement. Does the experiment described contradict that?
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