Comment by Y_Y

There must be some reason PRL chose to publish this, but it's not apparent to me from TFA or the abstract, and I'm not interested enough to login via my institution.

It's not new that you could set up co- or counter-rotation in such a system. This seems like the sort of thing G. I. Taylor had as a bath toy.

Maybe impossibly tiny and unresponsive torques are useful somewhere?