Well I wonder how Bitcoin difficulty adjustment will adjust itself once we have Quantum computing, that will target hard problem of every security algorithm/protocol. I know there are many IF and ELSE about Quantum computing and its no surprise as every new technology has to face some resistance initially. We need to have rational answer that why Quantum computing wont be affecting Bitcoin.
ASIC means "Application-
specific integrated circuit", so I guess that something designed specifically for a task will ever be more efficient than everything else (for the said task, hashing). Or maybe I'm wrong and ASICs will one day be replaced by something else, but I am not sure that Quantum computers could be more efficient than ASICs...