Apple shuttered the Advanced Technology Group, its research division, as a part of Jobs' consolidation and refocusing in the late '90s, and, as I understand it, research as an activity separate from product development hasn't really been part of the corporate culture since then. This does not mean lots of product-focused R&D doesn't go on throughout Apple, of course.

As far as I know Apple Research department was closed by Steve Jobs at some point, around ten years back. And have not been reopened. I have not seen any Apple employees recently presenting at academic conferences or collaborating with other researchers. Nor have I seen any publications.