To my knowledge only CA ballots have watermarks. There is a pdf document on their government website with a description. Ballots are printed by every state separately and not at a federal institution. Also watermarks are not printed. They are implemented during the production process of the paper. Too many people would have been involved to keep it secret. And all these quantum based stuff is a phantasy b/o the way the ballots are printed. Ballots are responsibility of the 50 states. So that theory has a big hole. Future will tell.