Why are we assuming China is too gullible to know this technology can never work, when it's so obvious to the lay HN commentariat?

Presumably we're cunningly exploiting specifics of their world view.

Despite the authoritarian rule, PRC still values education highly in quite a few contexts where it doesn't interfere too much with the authoritarianism, and the country not only has plenty of physics graduates who will have learned about the Josephson effect, but might well listen to them and give them adequate grants for R&D.

It's hard for people to imagine someone can be smarter than they are.