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*To*: [email protected]*Subject*: Re: quantum Computing*From*: [email protected] (Graham Toal)*Date*: Wed, 18 May 1994 17:47:34 +0100*Sender*: [email protected]

this term keeps poping up recently. Can anybody give me a pointer to where I can find out more info? Someone said that it is nonsense, "quantum computers?, Isn't that something out of a carlos casteneda novel?" I'm just trying to find out the real deal. It's purest bullshit: there are a class of mathematically difficult problems called "NP-Complete". These problems are all equivalent to one another in difficulty, ie if you can solve one you can solve them all (that's where the complete part comes is - it's NP-complete if you can prove that equivalence to another NP-complete problem). The "NP" part is "Non-deterministic, polynomial time". What that means is that there is a solution possible in polynomial time (rather than exponential time) *ONLY* on a *NON-DETERMINISTIC* machine. And that's the fun part, because a non-deterministic machine is one that *guesses* the correct path every time it has a choice to make. It's like trying to guess a 3-bit number, and saying "Is the first bit a 1?" Yes! "Is the second bit a 0?" Yes! "Is the third bit a 0?" Yes! Clearly, in real life, this doesn't happen. However, in fairy-tale land (or quantum physics as it's called) such things *can* happen - because one interpretation of the Einstein-Podolsky-Rosen thought experiment is that every time you make a choice based on the outcome of a quantum event, you fork off a pair of universes! In one universe you make one choice; in the other universe you made the other choice. Consequently if you loose a computer on such a problem, in *one* of the many many universes it generates, it'll find the right answer in polynomial time. The basis of quantum computing as a means to crack NP-complete problems therefore reduces to finding which of these universes found the answer and comminicating that answer to all the other universes. (Of course, you don't have to do this part, but the 99.9999999999999999999999999999999% of experimenters in all the universes that didn't find the result are not going to believe the method words too well...) Basically, it's a theoretical result with no application in the real world, and if ever anything happens that makes it mappable to the real world we'll have been subjected to such a major upheaval in the way the universe works that no-one will give a damn any more about such trivial things as encryption because we'll all effectively have turned into magicians :-) G

**Follow-Ups**:**Re: quantum Computing***From:*Rick Busdiecker <[email protected]>

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