> There are some engineers who think that although quantum processes do occur in the quantum computers of the various types being built, none will ever turn out to be useful (in doing really big tasks - whether factoring huge integers or finding minimum-distance traveling-salesman paths). On big problems they will just return random answers that are only "close" at best.
> It is doubtful (to some) ANY of them, (IBM, Google, ...) will work for factoring big numbers. (You might have to run them returning false results after false results for a long time until you get a true answer - because of the noise.)
> In some cases, like factoring big numbers, it's easy to check the answer classically.
> The checking part is not the issue. The issue is how much time a QC will need to run (the noise wiping out the parallelism) to find a correct factorization vs. a standard computer (even with quantum chip QRNGs for generating random numbers for a probabilistic factorization program, like Dixon's factorization).
> But this theoretical quantum parallelism speedup will be wiped out (according to critics) in an actual quantum computer due to "environmental" noise when the number of qubits is large enough to do something useful.
> If the the "superpositions" (needed to grow exponentially to get quantum speedup via parallelism) are physically wiped out (in a real QC with more than a few qubits), I don't see how any error correction can help.
On 14 Dec 2019, at 17:55, John Clark <johnk...@gmail.com> wrote:On Sat, Dec 14, 2019 at 7:52 AM Philip Thrift <cloud...@gmail.com> wrote:> There are some engineers who think that although quantum processes do occur in the quantum computers of the various types being built, none will ever turn out to be useful (in doing really big tasks - whether factoring huge integers or finding minimum-distance traveling-salesman paths). On big problems they will just return random answers that are only "close" at best.That's true for the sort of machines that D-Wave makes that use Quantum Annealing, that's good for some specialized problems but Quantum Annealing is not Turing Complete and D-Wave never claimed it was; devices like that might not be able to find the perfect solution to the traveling salesman problem but they could find a very good one and that is nothing to sneeze at. However to run Peter Shor's factoring algorithm you need a Quantum Computer that is Turing Complete,
and those are the types of machines that IBM, Google, and others make. As far as I know D-Wave is the only company that makes Quantum Annealers.
John K Clark--
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On Mon, Dec 16, 2019 at 5:49 AM Philip Thrift <cloud...@gmail.com> wrote:> If the the "superpositions" (needed to grow exponentially to get quantum speedup via parallelism) are physically wiped out (in a real QC with more than a few qubits), I don't see how any error correction can help.Conventional error correcting works mainly through clever use of redundancy,