Dwave quantum computers at 512 qubits should run some algorithms that achieve a speed advantage I'm some cases. However, there are a lot of supercomputers and a petaflop scale machine could come down to $10 million prices in the next year. The main utility of the quantum computers will be to run unique quantum algorithms that enable improvement of classical computer operation. (This information is mainly from a personal interview with Geordie Rose, CTO of Dwave.
An example is that non-convex algorithms can be run more efficiently to remove misclassified images in image recognition training datasets. This will enable classification and searches of images to be improved using regular classical algorithms.
If there are 1 million images that were classified by humans and 1% were wrongly labelled and the quantum computer could effectively remove the ones that were wrong then the image searches would be improved. Google has been cooperating with Dwave on research to prove out these methods.
So a combination of more qubits, faster machines, better algorithms and experience operating the machines and learning what they are best at should lead to success.
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