* Phys. Rev. Lett. 117, 130501 (2016) * 5+15 pages. This paper builds upon and mostly supersedes
arXiv:1507.08482. In addition to results provided in this previous work, here
we achieve learning improvements in more general environments, and provide
connections to other work in quantum machine learning. Explicit constructions
of oracularized environments given in arXiv:1507.08482 are omitted in this
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