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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

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.

Dylan16807 9y ago
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.
- jessriedel 9y ago
  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/nature12290.html https://www.nature.com/nature/journal/v499/n7457/full/nature... Although this case was egregious, more subtle shenanigans are rampant in the field.

Dylan16807 9y ago

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.

jessriedel 9y ago
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/nature12290.html https://www.nature.com/nature/journal/v499/n7457/full/nature... Although this case was egregious, more subtle shenanigans are rampant in the field.