back to article China launches quantum satellite to test spooky action at a distance

China has launched a satellite dubbed “Micius” that bears the Quantum Experiments at Space Scale (QUESS) instrument it will use to test quantum communications between Earth and space. QUESS' key payload is entangled photons. A quick primer: if you fire a photon at certain crystals it will split into two photons. Both of those …

  1. bazza Silver badge

    Hmm, I wonder how they're going to keep the photon carried aloft going without it being absorbed, scattered, etc. etc. It takes quite a long time (relatively speaking) to put a bit of kit in a rocket, launch it, get it stable in orbit.

  2. frank ly

    As I understand it

    The key exchange would be using a particular property of a quantangled photon link which ensures that any attempt to monitor the exchange would be detected; hence this is suitable for secure exchange of keys, if a bit slow compared to other communication methods and quite expensive.

    From what I've read, the instant and 'spooky' communication at a distance can't be used for the instant transmission of data at a distance, for various practical and physical reasons.

    I'm just a dog-basket physicist; a proper armchair physicist will be along in a minute.

    1. Mage Silver badge

      Can't be used for the instant transmission of data

      Lies for children explanation as to why it doesn't give Instant communication:

      Essentially you have two randomly shuffled packs of cards that you have NOT looked at. The change to the entangled particles essentially is the same as if both packs of card are re-ordered (and still match).

      When you look to see the order the entanglement is lost.

      Thus by being clever you can tell if quantum entangled communication has been tampered with (a man in the middle attack may be impossible), but actual transmission of actual information is limited by light speed.

      So an "ansible" or other faster than light communications isn't stopped by practical limitations but by basic physics. Only entangled particles ever "know" there has been a change. The two observers can agree to look at the same time and compare results. Obviously the agreement to look and the measurement of state are both communications limited to light speed or slower.

      Like all quantum mechanics, just when you feel you've grasped it, you realise it's not comprehensible.

      1. Destroy All Monsters Silver badge

        Re: Can't be used for the instant transmission of data

        Like all quantum mechanics, just when you feel you've grasped it, you realise it's not comprehensible.

        Some people disagree

        Why is "ResearchGate" infecting the search results? The main occupation of those guys seems to pretend to offer papers behind a wall of e-mail address collection and a forced "collaboration" tool. DIE, RESEARCHGATE.

  3. Destroy All Monsters Silver badge


    "Almost miraculously, any change to the first photon will be mirrored in the second. Just how that change propagates across space and time is not understood. It's also thought that whatever it is that lets entangled photons share information may take place faster than the speed of light."

    That kind of explanation puts the explainer firmly in a "General Relativity" universe, where little things are tracing their wobbly spaghetti paths through spacetime and things only happen if other little things are exchanged (there must be "interaction"). In QM, the "state" of the "duplicated photon" is one (mathematical) thing not at all visible "in reality" and extracting a bit of information about that thing changes it - so that you know more about the next bit of information that you may extract from it.

    Indeed, that changing of the thing "may" (indeed, does) not only take place "faster than the speed of light" (at the speed of thought, so to say) but across time, too (Quantum Weirdness Now a Matter of Time).

    Einstein himself described this as "spooky action at a distance (“pukhafte Fernwirkung").

    That's "spukhafte Fernwirking" (like in "spook", ghostly). Einstein was never happy with QM and desperatly wanted "action". There ain't no such thing.

  4. PK

    Three Body?

    So with this and a rumour of a planet in the Centauri system, it's beginning to sound like the Three Body Problem ...or are China just starting up the publicity for next year's film?

    1. Mage Silver badge

      Re: Three Body?

      missing l on rumour link

      1. PK

        Re: Three Body?

        Yes, took me several attempts to get it right. Need more coffee...

  5. Anonymous Coward
    Anonymous Coward

    Spooky action at a distance

    Like the wife calling you up at home when you are on the PC but should be doing the yard work?

    1. Arthur the cat Silver badge

      Re: Spooky action at a distance

      Like the wife calling you up at home when you are on the PC but should be doing the yard work?

      That's just spousal telepathy. It's carried by virtual guiltons.

  6. Anonymous Coward
    Anonymous Coward

    s/China being China/government-funded research being government-funded research/

    Isn't ElReg draping itself in its Rule Britannia stance more than ever, inserting a "blame the EU" or "China is evil" bit anywhere it can - even when the exact same thing are done by the UK?

    1. Anonymous Coward
      Anonymous Coward

      Not at all.

      Sometimes, it is also the Fault of Trump (FoT)

  7. Mutton Jeff


    Make it so!

  8. allthecoolshortnamesweretaken

    Clever ploy by space agency to get additional funding out of the spook's budget?

  9. Joefish

    Quantum mechanics for Gnomes.

    1. We put one shoe in a satellite and launch it into space. And when we look in the box and see which shoe we have left, we find the one in the satellite, way up in space, is miraculously its exact pair!

    2. ...?

    3. Profit.

    1. TitterYeNot

      Re: Quantum mechanics for Gnomes.

      "And when we look in the box and see which shoe we have left, we find the one in the satellite, way up in space, is miraculously its exact pair!"

      Unfortunately this would never work, as a pair of 'Quantum Entangled Shoes' TM are always left/right/left/right, and so will try to march off into the distance and inevitably trip up due to the entangled state of their shoelaces...

      1. Joefish

        Re: Quantum mechanics for Gnomes.

        This also explains an ancient mystery. To hurry an Englishman, one can command 'Left! Right! Left Right!' at a sharp pace. However, with three or four syllables in the words 'Aristera' and 'Thexia' it is fundamentally impossible to hasten a Greek...

        Even the Germans understand the importance of brevity in the words 'Links' and 'Rechts', yet with 'Sinistra' and 'Destra' one can begin to understand why the Italian army is always last to the battlefield.

        1. Anonymous Coward
          Anonymous Coward

          Re: Quantum mechanics for Gnomes.

          Being last to the battlefield is the signature of Good Civilization.

    2. michael cadoux

      Re: Quantum mechanics for Gnomes.

      Not comparable. The shoes are definitely left and right, but neither photon has a definite state. Until one is measured, each is in quantum superposition.

      Incidentally, I assume that photons are sent to the satellite, as the first poster's point about entanglement not surviving launch is surely valid?

      1. Joefish

        Re: Quantum mechanics for Gnomes.

        Since you cannot measure the state in any way that shows it to be indeterminate, you have no practical way of proving your assertion. While certain wave-like behaviours of a particle in 'quantum superposition' may suggest it exists in a perfect 50:50 superposition of two states, there is no actual evidence that the state it will collapse into when measured isn't pre-determined.

  10. Doctor Syntax Silver badge

    Meanwhile, spookily connected,

    Coincidence? Huh!

  11. Anonymous Coward
    Anonymous Coward

    MITM impossible

    Im not a physicist.

    I understand the deck shuffle analogy.

    However, what is unclear to me is how a MITM would be impossible.

    There are many ways to perform MITM attacks. Not all of them decrypt or read data on the fly.

    I understand that peeking at the deck is easy to detect but what if one didnt peek at the deck and simply captured the transmission for later analysis?

    Again, not physicist. Just a dumbass.

    1. Bluewhelk

      Re: MITM impossible

      If you have 'captured' the transmission for later analysis then one of two things happen...

      1) the photon will be absorbed by whatever detector you use and won't arrive at the destination.

      2) you split the photon using the crystals mentioned in the article and the and which ever photon you send on will be different, quantum state wise, to the original.

      In either case the interception in detected.

      1. Anonymous Coward
        Anonymous Coward

        Re: MITM impossible

        I don't know if this is possible, but is there a way to use your own photons and put them in a coherent state with the photons passing by, without looking at the state of any of them?

        If that is indeed possible to do, then providing you don't look at them until after the Chinese do, thus insuring they collapse the state and not you, you would have a copy of the key they sent.

        1. Anonymous Coward
          Anonymous Coward

          Re: MITM impossible

          I should add - I think this is probably not possible, but if so I'm curious to know whether it is "not possible given our current knowledge, but nothing in the laws of physics proves it impossible" or "not possible due to proven laws of physics".

        2. Francis Boyle

          Re: MITM impossible

          Look up the "no cloning theorem". Short answer:no. Slightly longer amswer: no, that's just the way quantum stuff works.

      2. Joefish

        Re: MITM impossible

        The theory seems to be that if a 'Man-In-The-Middle' intercepts the message, by capturing the photons, they then have to send on photons of their own to try and make the other end think nothing happened. (Note that the message is encoded by the photons themselves as with any optical data transfer; the message is not encoded by the quantum states, as they are impossible to fix).

        But they won't be able to replicate the quantum entanglements in the photons they send on, so if the sender measures the paired photons they kept, and the receiver measures the paired photons they received, and compare notes, they can tell if the message was intercepted and a fake copy passed on. However, this assumes they then have a perfectly secure way of exchanging the state data to do the comparison...

        Here's an interesting question - if you can measure the state of a photon without impeding its passage, does its quantum state collapse such that the dual-slit experiment stops working? i.e. This would mean you could tell if a photon has already had its quantum state collapsed by observation. So I presume not; that any such non-destructive attempt will, like the dual-split experiment, just yield a 50:50 result.

  12. I am the liquor

    it will be very interesting indeed to see how it goes once we can test it over 500km

    I'm pretty sure you can get things more than 500km apart without going into space.

    If you're in central London, Ipswich is further away than space. In more ways than one.

  13. DropBear

    The article's description of entanglement is not doing truth any favours. You can't "change" any of the entangled entities at will, not even once - all you can do is make a measurement on it, at which point all entanglement does is assure that whatever you would measure on the _other_ one would be related to whatever you got on this one. Influencing on purpose what you get on either end is NOT what entanglement allows you to do. How exactly the entangled entities "tell each other" instantly and at distance what the measurement's results should be is up for debate, what isn't, however, is that entanglement ends the instant you actively manipulate any characteristic of any of the previously entangled entities. There is no "entanglement telegraph", sorry.

  14. Oldfogey
    Big Brother

    Shutter telegraph

    So take a quantitly of entagled photons, display them (or their state) at both ends of your desired link in a grid.

    Considered an entangled pair to make their square on the grid white.

    Now interfere with selected photons at one end so that entanglement is lost. Those squares are considered black.

    Now read the message given by the black squares on the white background.

    Then replace the disentangled pairs with new entangled pairs and start again.

    Any attempt to interfere would initially make the message dificult to read, then impossible, as more bits were lost.

    1. Francis Boyle

      Re: Shutter telegraph

      The problem with all such attempts is that it's not possible to tell if an individual particle is entangled by looking at it. Any attempt to read the particle's state will simply ensure that it is no longer entangled. (It won't even tell you if it was previously entangled just that it not any more.) Entanglement is something you have to detect statistically.

  15. Anonymous Coward
    Anonymous Coward

    Common misquote

    Einstein was misquoted. It wasn't “pukhafte Fernwirkung", it was "pukhaff Eiknow".

  16. Little Mouse Silver badge

    A niche in time...

    So, "transmission" between an entangled pair is instantaneous. And I can also package one half up and send it into space, where it will be moving at silly speeds making it effectively younger than the other...

    Bingo! - I think I just invented quantum Resublimated Thiotimalene. Nobel prize here I come!

  17. Oldfogey

    Short answer...

    If you apply a Lorentz Fitzgerald contraction to one, but not the other, would that not break the entanglement?

    On the other hand, because of relativety, how do you know which one is moving fastest?

    Finally, no Nobel for you, as I will have invented Resublimated Thiotimalene last week - using it's Endochronic properties.

    1. Anonymous Coward
      Anonymous Coward

      Re: Short answer...

      If you apply a Lorentz Fitzgerald contraction to one, but not the other, would that not break the entanglement?

      We don't know but likely not.

  18. KLRajpal

    The assumption that the an electron-spin qubit (quantum bit) can be both spin-up and spin-down at the same time is based on an incorrect concept of Electron Spin.

    The assumption that a quantum switch can be ‘ON and OFF’ at the same time is based on an incorrect concept of Linear Polarization.

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