Right now, sure.. But eventually we will reach the apex of what we can do in classical transistor design. That day is coming.. Quantum computing could *potentially* offer a new avenue to go down. Maybe your iPhone 73 (Definitely not the 72S that thing was such a rip) could use this tech.. :)

If I put a working quantum computer in a box, then shake the box, what will actually be in the box? And where did my cat go?

Well, a quantum computer is a computer that exists and doesnt exists at the same time. The more you know about how it works, the less you know if you finished it or not. Happens all the time.