Re: Quantum computers
@"how do you go about checking the machine got the right answer"
DWAVE is an analogue computer running a sort of annealing algorithm configured using circuits and magnetic coils.
Lots of problems, that can be described as annealing problems, already have faster digital algorithms to solve them. So you can run the algorithm in a DWAVE as an annealing problem and in a computer using a different method, and see if the computer result is more optimal (i.e. better) than the DWAVE. So you know the DWAVE didn't return the optimal result.
IBM did this to diss DWAVE, pointing out that actually digital computers running digital algorithms are faster than DWAVE running annealing. Whereas DWAVE promoters generally compare DWAVE annealing to simulated annealing on a digital computer to claim the speedup. But that would only be faster for problems where no suitable digital algorithm exists.
The other way its done is to run an annealing algorithm in DWAVE and simulated annealing in a computer. And simply run the computer for longer till its result is better than the DWAVE. The computer doesn't need to get a perfect result, because we don't know the perfect solution. It only needs to get a *better* solution than the DWAVE to know the DWAVE didn't find the perfect solution.
Feynman, the physicist who coined the phrase Quantum Computer, did his work in the 50s and 60s, where computers were often analogue computers. And he imagined such a computer that could work instantaneously (using entanglement) and always get the optimal solution (using superposition). A sort of brute force that tries every possible solution.
DWAVE isn't that. It's a sort of annealing circuit.
It's also clearly not a quantum computer in the Feynman sense. No superposition and no entanglement. It's very clever marketing though.