learner vs quick study

learner and quick study both are nouns.

Word	Noun	Adjective	Verb	Adverb
learner	Yes	No	No	No
quick study	Yes	No	No	No

As nouns, quick study is a hyponym of learner; that is, quick study is a word with a more specific, narrower meaning than learner:

learner: someone (especially a child) who learns (as from a teacher) or takes up knowledge or beliefs
quick study: someone able to acquire new knowledge and skills rapidly and easily

Other hyponyms of learner include memoriser, memorizer, sponge, dweeb, grind, nerd, swot, wonk, tutee.

learner (noun)	quick study (noun)
someone (especially a child) who learns (as from a teacher) or takes up knowledge or beliefs	someone able to acquire new knowledge and skills rapidly and easily
works for an expert to learn a trade