I think it's closer to the 90s. The tooling to make very small features consistently already exists at good enough performance and they can fabricate much of th

I think it's closer to the 90s. The tooling to make very small features consistently already exists at good enough performance and they can fabricate much of this with the same systems used for traditional chips. Not the same materials being deposited, but they don't have to invent x-ray lithography and CVD/FIB/E-Beam Lithography/ALD/etc. The hard part is figuring out the best general engineering approach, i.e. what to make the qubits out of, how to entangle them, what materials to use. Once you figure that out and do small demonstration units I'd fully expect the right design to be scalable quickly. But the actual production of the right design should be less of a barrier. Still a barrier, but nowhere near 50s levels.