How fast will a quantum computer be?
Wed, 23 Sep 1998 10:52:41 -0700

What are the predictions about the speed of a quantum computer? I'm asking for a specific reason. I thought of a brute-force algorithm yesterday for general design of anything, but it would take super-massive computing power to be workable.
The algorithm is this: suppose you want to design a ship that can go half the speed of light, sustain 25 people, and cost less then a million dollars. Suppose ship designs are stored as some sort of CAD file, and you have a program which can look at a given CAD file and determine if it is a ship that can sustain 25 people, if it can reach half the speed of light, and if it costs less then a million dollars. So then you start counting, in binary code (0, 1, 10, 11...), and treat each sequence of 0s and 1s as a CAD file, and see if it fits the requirements that you specified, then return the best match. (This is pretty much the standard "brute force" technique for algorithms). Obviously this is completely unfeasable on any computer we have today. I think "the age of the universe, squared" would be a conservative estimate on how long it would take to do such a calculation. If you set the upper llimit on file length to be 1 gigabit, that's 2 to the power of 1 billion possibilities to calculate. But I wonder if something like a parallel quantum computer the size of jupiter might make even that many possibilities something that could be calculated within a tolerable stretch of time. Even if the calculation still took something like 20 years, it would be amazing. We could then use the same technique to say "write me an algorithm that can do the same thing as the brute force CAD design algorithm, but faster. Return the fastest result."

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