Quantum computing
Robert J. Hansen
rjh at sixdemonbag.org
Fri Apr 20 02:25:10 CEST 2007
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> Which I also remarked in the original post. However, when (if?)
> commercial interests grab a hold of quantum computing, huge leaps in
> cost of production perhaps could be achieved, making memory-rich
> quantum
> computers abundant -- at least, from my chair, there's no
> obstruction to
> this future. (?)
Eh. I'm still unconvinced. It wasn't until last year that the final
physics hurdle to large-scale QC was addressed (large systems have a
strong tendency to near spontaneously decohere, turning your quantum
computer into an expensive paperweight). We still have no idea how
to apply this physics knowledge, however.
Just knowing that something is possible doesn't mean the ability to
do it is around the corner. We can teleport atoms in laboratories at
the speed of light and we know how to do it for macro-scale items,
but the engineering difficulties are so large that I doubt we'll see
it in our lifetimes.
While I agree that commercial development _may_ lead to developments
in QC, I think it's equally likely that the engineering difficulties
will be insurmountable. Which means that, from where I sit, we
should just shrug and say "we really can't say with any confidence
what the future will or will not hold".
> found -- this pragmatism causes me to ponder the scenario in which
> something like Rice' theorem could be established for quantum
> computers'
> ability (or traditional computers' inability):
What do you mean? Rice's theorem applies to QC.
Computational theory is computational theory. We've already got very
robust mathematics to describe the computational properties of QC.
We know that BQP is a superset of P, that it does not encompass NP-
COMPLETE, that it has some overlap with NP, etc., etc.
It's true that in mathematics there could always be a proof delivered
tomorrow by some hungry graduate student which will utterly shatter
our knowledge of math as we know it. But this is true for all of
mathematics. It's not as if this risk is special to QC. You should
be just as concerned about the prospect of P=NP.
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