(a) Like all great conspiracy theories, it would require too many people to keep their mouths shut; and (b) nobody in China would care about any secrecy rules l

(a) Like all great conspiracy theories, it would require too many people to keep their mouths shut; and (b) nobody in China would care about any secrecy rules laid down by the US government, any more than Sakharov's team in Russia cared about the US's intention to monopolize the hydrogen bomb. The closest thing to this type of technology would be EUV hardware of the sort produced by ASML. We have now given China every incentive to put everything they've got into developing similar technology on their own soil. Despite slow progress to date, they will get there. Another analogy might be the math behind encryption, effectively monopolized by NSA for decades... but nobody's trillion-dollar economy was blocked by those secrets.