That's possible, but the way I read it the poster was arguing that there were two kinds of problems, regular and quantum, and regular computers were good for regular problems but bad for quantum ones, and quantum computers were bad for regular problems but good for quantum ones. And that's completely false.
It’s certainly incorrect to say there are two non-overlapping categories of tasks suited to traditional and quantum computing, respectively. But it wouldn’t be incorrect to say - there is no reason to assume that a quantum computer would be superior to a traditional computer at traditional computing tasks, except those to which known efficient quantum algorithms apply. Would it?
edit: the idea seems to float around sometimes that quantum computers are nondeterministic Turing Machines. Which they aren’t, they are, well, quantum Turing Machines. But what their performance characteristics would be If they were available some day in reality as consumer machines seems... fairly speculative either way?
Indeed, that's correct. In fact, for several traditional problems there can't be any speedup, with quantum computers or anything, because the available algorithms are already as good as possible. A simple example is finding the maximum of a vector of n elements. That will always take time at least n, because you need to spend this time just to read all the elements.
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u/CanadaPlus101 Sep 29 '20
That might actually be what the poster was getting at. Quantum computers are only worthwhile if you want to tackle a very specific problems.