The Manhattan project employed some significant % of all of America. A project of that scale will likely never happen again.
It was also about far more than the science. It was about industrializing the entire production process and creating industrial capability that simply did not exist before.
I am skeptical you could do something of that scale for 30B today. That is just the dollar cost based on inflation. If you used CPI indexing probably hundreds of billions to a trillion dollars now.
Does quantum computing need that though? We don't suddenly need a large, unique supply chain for these computers. We don't need to dig up the qubits and refine them. Testing doesn't blow up the computer.
The Manhattan project had a huge impact but it was not that big as far as efforts in the war went (they managed to hide the budget allocated to the project from most of congress, for example).
It was like 0.5% GDP. It wasn’t insane, but still, you are right.
It was very focused. What do we get out of the F-35 program? By comparison, it has eaten (projected total lifetime cost) 2 trillion dollars. It is 4.5% of the GDP. I had no idea. This is just a military and government contractor subsidy. What are we doing…
It was also about far more than the science. It was about industrializing the entire production process and creating industrial capability that simply did not exist before.