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Comment by Dylan16807 | Hacker News Reader

Normal transistors are using quantum effects too.

The whole point of a "quantum computer" is getting those nonlinear speedups. If the entanglement doesn't speed anything up then it's pretty close to the beaker in terms of relevance.

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> Normal transistors are using quantum effects too.

Well, I mean, I think it's more like "we're well aware of quantum effects and they're parasitic". I've yet to see a production TFET or something like that which actually uses a quantum phenomenon as the operating principle of the switch.

Isn't the band gap a fundamentally quantum phenomenon?

I'd say yes

In the same way you're being supported by electromagnetic forces when you're standing or sitting on something

but you don't need to understand much to just physically exist. Whereas electrodynamics and certainly also quantum effects in semiconducting cristals informed the development of transistors in the last what, 50-60 years.

Remember, what we are talking about is expressly using the features of quantum theory, superposition, entanglement, etc as a computing resource. This is not at all the same thing as when people say things like 'we design computers with quantum theory' or the like.

You can divide it into three classes, really.

A) Uses quantum effects like superposition and entanglement to compute, no quantum speedup.

B) Uses quantum effects to compute, with quantum speedup.

C) Universal quantum computer with quantum speedup.

I would argue that the term "quantum computer", as commonly used, requires the device to be at least class B on this list. Even if you don't think class C is necessary, class A is full of trash like "knockoff 6502 with a fancy photon-splitting ALU". Class A allows the quantum nature to be a pointless novelty resource. It's like a "solar-powered" house with one square foot of panels.

And as far as I know D-Wave haven't conclusively proven their device to be class B.

I don't believe they've proven class A. Just because you have a device that computes something and that devices has entanglement does not mean you've exploits the entanglement to compute anything in any useful sense. An extreme example: you can prepare a superposition and measure it to generate a random classical bit (0 or 1), and you can use that as a source of entropy for a classical probabilistic algorithm, but it would be ridiculous to call this a "quantum computer" of any class.

In fact, multiple experimental groups did essentially this, which some theorists at IBM (former colleagues of mine) called them out for:

https://www.nature.com/nature/journal/v499/n7457/full/nature...

Although this case was egregious, more subtle shenanigans are rampant in the field.

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