"AARG!Anonymous" wrote: > > The problem is that you can't forcibly collapse the state vector into your > wished-for eigenstate, the one where the plaintext recognizer returns a 1. > Instead, it will collapse into a random state,
Sorry, that's a severe mis-characterization. > David Honig wrote: > > >I thought the whole point of quantum-computer design is to build > >systems where you *do* impose your arbitrary constraints on the system. David Wagner wrote: > > Look again at those quantum texts. That's good advice. > Quantum doesn't work like the original poster seemed to wish it would; > state vectors collapse into a random state, Random is not the right word. > not into that one magic > needle-in-a-haystack state you wish it could find. C'mon folks, let's cut down on extreme statements like the-whole-point-is-this or the-whole-point-is-that and using words like "magic" to describe finding the right answer. 1) Computer design has many points that must be taken into consideration. Quantum computer design is in some ways more powerful but in other ways more constrained than classical computer design. 2) One of the points is that yes, the computer should compute what you want it to compute. OTOH it takes more than wishing to bring such a computer into existence. 3) A sufficiently well designed quantum computer can, in principle, find some needles in some haystacks, precisely because the structure of the machine, acting according to the laws of quantum mechanics, does in fact "collapse" the wave-function into a representation of the wished-for answer. (PS most of what has been written about "collapse" of wave-functions is baloney, but we need not pursue that tangent just now.) ================= A general remark about parallel computing: For every parallel algorithm (running on P processors) there exists a corresponding uniprocessor algorithm: just set P=1 and turn the crank. The converse does not hold. The existence of a uni- processor algorithm may or may not be a guide to the creation of a parallel algorithm. As Brooks famously said, creating a baby requires nine months, no matter how many mothers are assigned to the task. The same applies even more strongly to quantum computing: It would be nice if you could take a classical circuit, automatically convert it to "the" corresponding quantum circuit, with the property that when presented with a superposition of questions it would produce "the" corresponding superposition of answers. But that cannot be. For starters, there will be some phase relationships between the various components of the superposition of answers, and the classical circuit provides no guidance as to what the phase relationships should be. So let's not guess about what quantum algorithms exist. It is possible to construct such algorithms, but it requires highly specialized skills. --------------------------------------------------------------------- The Cryptography Mailing List Unsubscribe by sending "unsubscribe cryptography" to [EMAIL PROTECTED]