Posted on 07/31/2011 7:28:30 AM PDT by decimon
The quantum world allows you to answer questions correctly when you don't even have all the information you should need
No-one likes a know-it-all but we expect to be able to catch them out: someone who acts like they know everything but doesn't can always be tripped up with a well-chosen question. Can't they? Not so. New research in quantum physics has shown that a quantum know-it-all could lack information about a subject as a whole, yet answer almost perfectly any question about the subject's parts. The work is published in Physical Review Letters.
"This is something conceptually very weird," says Stephanie Wehner of the Centre for Quantum Technologies at the National University of Singapore, who derived the theoretical result with PhD student Thomas Vidick at the University of California, Berkeley, United States. It's a new phenomenon to add to the list of philosophical conundrums in quantum physics – as strange as the quantum superposition or the quantum uncertainty principle. But the work also has practical motivation: understanding how information behaves in the quantum context is important in emerging technologies such as quantum cryptography and quantum computation.
To frame the problem, consider the example of someone answering questions about a book they have only half-read. If someone has incomplete knowledge about a book as a whole, one expects to be able to identify the source of their ignorance somewhere in the book's pages.
Wehner and Vidick simplify the situation to a book with two pages. They invite the usual quantum players, Alice and Bob, to collaborate. Alice reads the book and is allowed to give Bob one page's worth of information from it.
If Bob only has classical information, it is always possible to work out what he doesn't know. "We show that classically things are, well, sane" says Wehner. In other words, Bob's ignorance can be exposed. Imagine that Bob is a student trying to cheat in an exam, and the notes from Alice cover half the course. An examiner, having secretly inspected Bob's crib notes, could set questions that Bob couldn't answer.
The craziness comes if Bob gets one page's worth of quantum information from Alice. In this case, the researchers show, there is no-way to pinpoint what information Bob is missing. Challenge Bob, and he can guess either page of the book almost perfectly. An examiner could not expose Bob's ignorance even having seen his notes as long as the questions cover no more than half the course – the total amount of information Bob can recount cannot exceed the size of his notes.
It is an unexpected discovery. Researchers had been trying to prove that quantum ignorance would follow classical intuition and be traceable to ignorance of details, and finding that it isn't raises new questions. "We have observed this effect but we don't really understand where it comes from," says Wehner. An intuitive understanding may be forever out of reach, just as other effects in quantum theory defy mechanistic description. However, Wehner and Vidick have begun to design experimental tests and are already formulating a range of ways to explore this strange new frontier. In this work, they devised a means of encoding the quantum information from two pages into one that gave Bob, the quantum know-it-all, the ability to recount all but one bit of the information on either page (the last bit Bob would have to guess). They plan to test whether other encodings would be equally good.
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Journal reference: T. Vidick and S. Wehner, "Does Ignorance of the Whole Imply Ignorance of the Parts? Large Violations of Noncontextuality in Quantum Theory", Physical Review Letters 107, 030402 (2011); http://prl.aps.org/abstract/PRL/v107/i3/e030402. A free preprint is available at http://arxiv.org/abs/1011.6448.
For more information, please contact: Stephanie Wehner Principal Investigator and Assistant Professor Centre for Quantum Technologies National University of Singapore Email: wehner@comp.nus.edu.sg Tel: +65 6601 1478
National University of Singapore
A leading global university centred in Asia, the National University of Singapore (NUS) is Singapore's flagship university which offers a global approach to education and research, with a focus on Asian perspectives and expertise.
NUS has 15 faculties and schools across three campus locations in Singapore – Kent Ridge, Bukit Timah and Outram. Its transformative education includes a broad-based curriculum underscored by multi-disciplinary courses and cross-faculty enrichment, as well as special programmes which allow students to realise their potential.
NUS has three Research Centres of Excellence (RCE) and 21 university-level research institutes and centres.
It is also a partner for Singapore's 5th RCE. The University shares a close affiliation with 16 national-level research institutes and centres. Research activities are strategic and robust, and NUS is well-known for its research strengths in engineering, life sciences and biomedicine, social sciences and natural sciences. It also strives to create a supportive and innovative environment to promote creative enterprise within its community. More at www.nus.edu.sg.
Centre for Quantum Technologies at the National University of Singapore
The Centre for Quantum Technologies (CQT) was established as Singapore's inaugural Research Centre of Excellence in December 2007. It brings together quantum physicists and computer scientists to explore the quantum nature of reality and quantum possibilities in information processing. CQT is funded by Singapore's National Research Foundation and Ministry of Education and is hosted by the National University of Singapore (NUS). More at www.quantumlah.org.
Is this why my Kindle is missing random pages? And because the page number is not shown before or after the missing pages I can never determine exactly which pages are missing? I wonder what will happen if I hold a paperback version next to it and see if the systems interact. Flipping paper pages will determine which electronic page numbers can be seen?
Einstein was reportedly stopped by the same police officer and answered "according to my reference frame, officer, I was standing still and YOU were speeding past me." The confused officer then wrote himself a ticket.
Same people who say that over very long periods of time, all variables average out to be constant?
Perhaps as the universe expands the quantum fabric of space (quantum 'foam'/vacuum energy) thins and its properties change.
I'm not sure the 'expansion' of the universe is an accurate assumption.
Maybe the chaos (differences in potential) is what provides the quantum foam/energy that is what makes matter/the Universe exist.
As usual, the most important things in our Universe are the smallest and hardest to see, ergo the hardest to understand.
They mistakenly gave you the experimental Quantum Kindle. The very act of viewing some pages makes them move elsewhere.
I had to reread it, but this appears to be no more than a theoretical physicists theoretical thought experiment. There doesn’t seem to be any science here, only postulation. It’s interesting in its own right, but really is not a science story about quantum mechanics.
I’m not fond of academics dweebs, but when you write a response like that it just shows you to be the ignorant one due to your lack of understanding of the subject matter. If you spent the time to understand quantum theory and then wrote a reply, you would find the humor in this article much more interesting. But you choose to write a post calling the author an idiot only because you don’t understand the subject. This is sad to see at FR.
Based on my EPR and Uncertainty Principle followup posts, it should be obvious that I DO understand the subject to some degree. If you knew anything at all about the subject you would have realized that. Clearly you don’t. The author is an “idiot” because he presented the story, which was supposed to be a QUANTUM PHYSICS one, as some other dopey thing, failing to get into any detail whatsoever about the actual scientific finding. I’d bet you don’t have the foggiest idea either of what the finding was.
I read your follow-ups and it still didn’t give any indication of your knowledge of the subject. Perhaps you’re a better physicist than a writer.
My apologies.
It's only as abstract in its formulation as it needs to be. In a sense it's an expression of ultimate pragmatism. Feynman takes this approach in his Lectures on Physics. He counseled that one should simply learn to use it, and not try to "understand" it, "... or you will go down the drain into a blind alley from which no one has ever escaped." ( from The Messenger Lectures, not the L on P. )
I absolutely agree. Or maybe not.
Yes, it works, or so they say. I’m not sure that anyone would be able to convince them that it doesn’t, even if it did not.
Sure it works, and works great. It’s fabulous. Couldn’t have built the internet without it ... and lasers ... MRI’s ... and don’t forget its founding achievement, explaining the spectrum of incandescent light, followed shortly by the atomic spectra, including all their multifarious subtleties.
I mean ... it works!
These claims that you couldn’t have the internet and lasers and MRI’s is just another example of what I was talking about. Grandiose claims that are easily uttered, but not so easily proven or disproven except to a very tiny part of the population, who are very invested in these theories. But it’s the quantum weirdness part that is the most difficult to accept. They claim to have proven it experimentally, but I suspect that some day, the quantum weirdness idea will be regarded as a wrong turn that took decades to correct. Maybe it’s just my suspicion with the art of statistics. It’s too easy to manipulate statistics or misinterpret them. It’s happened many times before. The global warming thing is a pretty good example.
It's called confabulation. Old drunks are masters at it.
I should think we are all invested in QM, as much as we are invested in Newton and Galileo. Solid state physics was founded by Felix Bloch in 1928 when he described the basics of electronic band structure in solids, just 2 years after the introduction of Schrodingers equation.
The transistor wasn't invented by theorists, and I'm sure there was a lot of empirical thinking that went into it, but all this thinking had to be in terms of the quantum theory of solids, simply because there has never been any other theory remotely capable of accounting for the phenomena being manipulated.
The laser wasn't invented until the sixties, and again the thinking required was entirely in terms of quantum states and transitions. The same goes even more for MRI's which is based on the technique of NMR, which is a can't be thought of in any but quantum terms.
But it’s the quantum weirdness part that is the most difficult to accept. They claim to have proven it experimentally, but I suspect that some day, the quantum weirdness idea will be regarded as a wrong turn that took decades to correct.
It was experiment that drove the founders of QM into acceptance of its counterintuitive aspects in the first place. The recent ballyhoo of proofs and demonstrations of it are in the nature of "failures to disprove" it under extreme and rarefied conditions, which used to be considered "thought experiments".
I always say, just look at a Sodium vapor streetlight through a diffraction grating ( which is no more than a piece of film in a slide photo holder, ) and see the emission "lines" ( separate images of the streetlight in this case. ) That's the original quantum weirdness, the quantum jump, which is in complete contradiction to any conceivable theory of continuous point motion. The explanation of these emission lines in fact served to establish the axioms of QM by the mid 1920's, and there ensued an explosion of scientific understanding and technology eclipsing all that came before. Why you would want to think of this development as some kind of mistake is beyond me.
(Now sinking rapidly to the bottom of my "to do" pile.)
Cheers!
[Rim shot]
Well done, dr. lew; now here's a poem for the two of you.
Schrödinger's cat's a mystery cat, he illustrates the laws;
The complicated things he does have no apparent cause;
He baffles the determinist, and drives him to despair
For when they try to pin him down--the quantum cat's not there!
Schrödinger's cat's a mystery cat, he's given to random decisions;
His mass is slightly altered by a cloud of virtual kittens;
The vacuum fluctuations print his traces in the air
But if you try to find him, the quantum cat's not there!
Schrödinger's cat's a mystery cat, he's very small and light,
And if you try to pen him in, he tunnels out of sight;
So when the cruel scientist confined him in a box
With poison-capsules, triggered by bizarre atomic clocks,
He wasn't alive, he wasn't dead, or half of each; I swear
That when they fixed his eigenstate--he simply wasn't there!
Cheers!
What I meant by “invested” is that there are only a few who claim to understand all this, and they make their living by understanding it. If they suddenly realized, “It doesn’t work,” I would not necessarily feel comfortable that they would tell us. And if it did not work, I would not feel comfortable that they would realize it.
Having said that, it does appear to be the prevailing view, and I certainly don’t have the proof that it’s wrong.
Do you have any research you can point me to about the defraction grating? I think the only thing I’ve read about that was Feynman’s explanation in Quantum Electrodynamics. It’s been a while, but I don’t remember thinking at the time that it proved quantum mechanics. I guess I don’t think of the idea of a discrete quantum is so amazing, so if it’s only that to which you are referring, then maybe it just did not surprise me when I read it.
It’s the idea that you can test the spin of a particle on one side of the universe, and instantly determine the spin of another particle on the opposite side of the universe without any kind of predetermination of those parameters that I find difficult to accept. I do not fully understand the mathematics of Bell’s theorem, but I suspect I would find it difficult to accept the spooky action idea even if I did. To me, the conclusions are so amazing that they must be wrong. Something must be missing. Rather than trying to come up with a string theory that can explain that, I would be trying to come up with a proof that it’s wrong.
Of course, I realize that a lot of researchers have tried to do that and failed, but then history is full of examples of incorrect experimental research that took the science on a rabbit chase.
By the way, how do you know so much about this?
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