I think a good way to think about sentences like that is that the word quantum is short for "belonging to quantum mechanics", like how "classical gravitation" d

I think a good way to think about sentences like that is that the word quantum is short for "belonging to quantum mechanics", like how "classical gravitation" doesn't mean that there's anything classic about gravitation. The quantum quantifier is there to differentiate the superposition they mention from "classical" wave superposition. It's very complicated stuff but not "very, very complicated" stuff, you can read Feynman's QED book (http://www.amazon.com/QED-Strange-Theory-Light-Matter/dp/0691083886 http://www.amazon.com/QED-Strange-Theory-Light-Matter/dp/069..., <$9 used with shipping) and obtain a pretty good working knowledge of things.