back to article Boffins measure 27 quantum states of light

One of the key tenets of quantum mechanics, that it's impossible to measure a quantum state without collapsing the wave function, has taken an arrow to the knee, courtesy of a University of Rochester experiment. Building on work carried out in 2011 at the National Research Council of Canada, the UoR researchers say they've …


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  1. Allan George Dyer Silver badge

    Improve quantum-based secure communications systems?

    Doesn't it break them instead? The whole point of quantum crypto is that observing the communication breaks it, but this says you can make a weak measurement and not change the state. Or am I missing something?

    1. Eddy Ito Silver badge

      Re: Improve quantum-based secure communications systems?

      From the Rochester page:

      "It does, however¬, give partial information on the health of the cat, which when repeated many times can lead to near certain information as to whether the cat is alive or dead."

      I look it as taking many blood samples and looking, for instance, at the oxygenation of the blood to determine if it's probably alive before opening the box and stabbing it in the brain with a volt meter to measure electrical activity. Sure, with each blood sample the cat's health may change but we'll still be able to measure something else when it comes time to burn the last bridge, or something like that.

      1. Charles Manning

        Better not take a change

        Give the cat another few whacks with the cricket bat/

  2. This post has been deleted by a moderator

    1. This post has been deleted by a moderator

    2. Anonymous Coward
      Anonymous Coward

      Re: Oh boy.

      Be nice .. QM causes enough brain-hurt to excuse minor language errors.

      If I wanted to go into full pedant mode I'd take issue with the entire 'collapsing the waveform' phrase since that reifies the copenhagen interpretation.

    3. diodesign (Written by Reg staff) Silver badge

      Re: Oh boy.

      There, fixed. Please email corrections@thereg next time you spot something.


      1. Thecowking

        Re: Oh boy.

        You don't need a degree in "Quantum physics" to understand it.

        I don't think any one really understands it.

        I can do the maths, but that's not the same as understanding it.

        QM is just _weird_

        Edit: My reply used to make sense, until the mods collapsed the waveform of some previous posts and it turned out that they were dead after all.

        1. Fred Flintstone Gold badge

          Re: Oh boy.

          You don't need a degree in "Quantum physics" to understand it.

          I don't think any one really understands it.

          Ah, but this poses a rather interesting problem if this is to be used in "secure" communication, and it is one we already have with existing crypto: who can tell that it is secure or not, and is not fitted with a clever backdoor?

          Who can we trust to (a) understand what is going on (personally, 13.5 states of undead for a cat give me a headache just to think about, but may make for novel zombie movie plots) and (b) be able to explain this in a way that others can verify and confirm?

          1. Anonymous Coward
            Anonymous Coward

            an 'A' in this topic means someone sucessfully pretended to understand it.

            Actually you don't need a degree in "Quantum physics" to understand it. This is a good video to learn about it. I lied, I still don't understand it.

  3. Denarius
    Thumb Up

    27 rings a bell

    irrelevant ? dunno. One theory of everything starts with 27 dimensions. Any connection ? At least it was not 42

    1. Destroy All Monsters Silver badge

      Re: 27 rings a bell

      No, it is just the size of a teeny tweeny Hilbert space.

  4. Anonymous Coward
    Anonymous Coward

    off topicish

    Ross Anderson (if you don't like him don't bother reading further) et al have set the cat among the pigeons with this:

    Some pretty pissed quantum mechanics out there!

    1. Destroy All Monsters Silver badge

      Re: off topicish

      > /why-bouncing-droplets-are-a-pretty-good-model-of-quantum-mechanics


  5. Dr Patrick J R Harkin

    I've said it before and I'll say it again...

    I understood every word of that.

    The actual sentences, on the other hand...

  6. Jedit

    You must have seen the movie, you must have read the book

    Did it never occur to Schrodinger that the cat was an observer?

    1. Matthew 25

      Re: You must have seen the movie, you must have read the book


  7. AceRimmer1980

    27 States?

    3 cats may have been harmed during the course of this experiment.

  8. All names Taken

    The quanta were aware of a nomenclature scheme based on 26 letter alphabet and thought they would play a joke on the researchers no?

    1. Colin Wilson 2

      Maybe they were Spanish?

  9. mark 58

    [quote]You can only view the cat as alive or dead [quote] - eerr... what the heck are you on about Mr Fry ? Famously misunderstood seems to apply to your article as well. Not a big fan of it, but check out the wikipedia entry for at least a coherent explaination.

  10. myhandler

    I read a book ages ago where Russian physicist Lazar Mayants said that QM theory was a result of misinterpreting the maths and that it was misleading.. he was described as 'fringe'.. but maybe he was closer. (Just think what this could do for the climate debate..)

    1. Destroy All Monsters Silver badge

      This discussion has been had and was buried dead.

      1. Tom 13

        Just because you buried one box doesn't mean both cats are dead.

        IIRC, the box had an independent oxygen supply for the trip through space, just to ensure the wave form didn't collapse before the box was opened.

  11. Nessalc

    Nobody understands...

    "I think I can safely say that nobody understands quantum mechanics." - Richard Feynman

  12. agricola

    All It Takes is a Galaxy-Sized Computer. The NSA Could Do It if They Had Spare Time

    Was there ever any salmon of doubt?

    Poor Heisenberg; Poor Physics Discipline; Poor Physicists; Poor Physics Students:

    now , instead of not knowing which of two states (I know, I know: at the same time) is the correct one, now we don't know which of twenty-seven states, at the same time, is the correct one.

    But this is great news for all the "quantum physics pseudoscientists": more fodder for their artificial intelligence.


    "Aachh!"--one can almost hear him exclaim--"This [(quantum physics) paper/hypothesis] is so bad, it's not even wrong."--Wolfgang Pauli

    "If you think you understand quantum mechanics, you don't understand quantum mechanics"--Richard Feynman


    1. Destroy All Monsters Silver badge

      Re: All It Takes is a Galaxy-Sized Computer. The NSA Could Do It if They Had Spare Time

      Oh God, why?

  13. Pascal Monett Silver badge

    27 Dimensions ????

    We can barely measure 4 properly, what on God's Green Earth makes them think they can measure 27 ?

    "Dimension" must not have the meaning I think it has.

    1. Destroy All Monsters Silver badge

      Re: 27 Dimensions ????

      Dimension = free variable.

      In classical space at time "t", 3 real-valued coordinates suffice to describe the position of a "mass point".

      With two particles, you need 6 real-valued coordinates. The space of two particles has 6 dimensions! (Why 3 + 3 instead of 3 x 3? Dunno, lol!)


      Same here: 27 complex values => 27 dimensions.

  14. Schultz

    Many measurements --> more classical physics

    A weak measurement will never determine whether Schroedinger's cat is alive. It can only determine the average probability of cats in Copenhagen (or at some large cat-containing place of your choice) being black or white. Spoiler alert: the answer is grey, unless you prepared the cats to be spotted, in which case the answer may be white with 17 grey spots.

  15. Anonymous Coward
    Anonymous Coward

    so Shrodinger is driving down the road and gets pulled over by a cop

    cop searches car: "I see there's a dead cat in the boot"

    "well there is now!" says Shrodinger

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