Prior to WWII the United States was the world's leading power in terms of Science, Engineering and Industry - not Germany or the British Empire. The reason that Central European scientists fled to America (and not Britain) is because the United States had the scientific, engineering and industrial base to absorb them. Consider some of the major scientific breakthroughs to come out of the US leading up to and coming out of the war: Nylon, Teflon, Synthetic Rubber, Penicillin, Solid State Transistors, Microwave Communication, Information Theory, a Vaccine for Polio... These all would have happened with or without the war and the migration of German scientists (though adding John von Neumann to the mix probably helped move things along).
> Prior to WWII the United States was the world's leading power in terms of Science, Engineering and Industry - not Germany or the British Empire
Per capita? The US had a larger population.
Being the leading power is about magnitude not intensity. The country that is twice as large and operates at a similar level of intensity will be the more dominant force (see also - China today). Per capita, I would bet on the Swiss (then and now) - though it will depend on the metric at that point and their output will be comparable to the Germans, British, French and the Americans.
> Penicillin
Invented and developed in the UK.
> Microwave communication
Lion's share of pre-war advances and development were in various European countries.
> Synthetic Rubber
Developed by Fritz hoffman at the Bayer Laboratory in Germany, 1906
Frankly, your comment is a massive self-own.
Prior WW 2, the US had even no notion of quantum physics. How could it be the world power in science?
The US definitely had a notion of quantum physics prior to WWII. Feynman got his PhD at Princeton in 1942 in Quantum Physics so I would assume that John Wheeler had some familiarity with the topic back then. I would mention that the most significant result of quantum mechanics is solid state transistors, and Shockley was awarded a phd for quantum mechanical applications back in the 30s.
Michelson and his experiments on the aether not existing were enormously influential to theoretical physics. “No notion” is incorrect, they had numerous home grown talents in physics, on top of the huge influx of talent from 1930s immigration of European scientists.
The USA being a beacon of hope and enlightenment in those days stands in stark contrast to the isolationist, anti-intellectual, anti-research, and frankly xenophobic policies pursued by the current admin, courts, and congress.