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Comment by kamilner | Hacker News Reader

The D-Wave machine is not a full adiabatic quantum computer, though (which would be polynomially equivalent to a universal quantum computer). It does quantum annealing over a pretty restricted set of Hamiltonians.

I think it is perfectly reasonable to say it is not a quantum computer, in the same way that not everything performing computation is called a computer. Otherwise---taken to the absurd---why not call a chemist's beaker a quantum computer?

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It's a computing machine taking advantage of certain quantum effects to do computing. Theoretically, it may be able to do certain tasks faster than a traditional computer

I'm not saying you're wrong- it's often mislabeled as a quantum computer- but it isn't fair to say it's no better than a chemist's beaker.

I guess the problem is that the general public doesn't really know the distinction between quantum annealing and universal quantum computation.

So maybe articles should include something like:

"The D-Wave system uses quantum annealing, which utilizes quantum effects to solve a select few problems much faster than traditional computers. However, it's not as flexible as a universal quantum computer, which could solve a much wider range of problems, including the prime-factorization problem at the heart of modern cryptography."

I think this is a pretty good summary for an article.

That's a pretty good summary, but honestly the vast majority of journalists will probably just run with the more sensational headline, and D-Wave is very happy to encourage that.

A potentially-enlightening analogy:

Is instruction pipelining a form of multiprocessing? (No.) Is hyperthreading? (Sort of, but it's limited and has a separate name for a reason.) Are hyperthreads marketed as SMP cores? (Of course.)

Is a chemist's beaker a quantum computer? (No.) Is D-Wave's device? (Sort of, but it's limited and should have a separate name.) Is D-Wave's device marketed as a quantum computer? (Of course.)

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.

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.

> 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.

a tunnel diode uses quantum effects, too, and the tiniest mosfets come close to the quantum realm at least in production, too. Does that make a pc a quantum computer? I really don't know the difference, but I'm sure that would be stretching it.

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