Not sure what you're referring to here. Maintaining a superposition is not hard. The light from distant galaxies has been in superposition across literally bi

Not sure what you're referring to here. Maintaining a superposition is not hard. The light from distant galaxies has been in superposition across literally billions of (light) years before we detect it. What is harder to maintain over large distances are entanglements, but even those have been maintained across hundreds of miles. When I talked about a "fundamental limit on how big you can make a quantum computer" I wasn't talking about it's physical size, I was talking about the number of mutually entangled qbits it contains, and the amount of time it is able to maintain those entanglements in a coherent state.