Will quantum computing change machine learning?

Then there are'quantum machine learning algorithms,' developed over the last decade following a breakthrough by Harrow, Hassidim, and Lloyd, which do address problems like clustering, classification, support-vector machines, etc. But these algorithms typically require a bunch of conditions to work: for example, that the data are well-conditioned; that they can be accessed in quantum superposition (for example, using a "quantum RAM") or else computed on the fly; and that the properties of the data one cares about can actually be estimated by measuring the resulting quantum states. And we don't yet know how often those conditions will hold in practical applications---and equally important, in the cases where they do hold, we don't have strong evidence that there couldn't be classical random sampling algorithms with similar performance to the quantum algorithms.