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Can a quantum money system exist in which bank (who possesses a secret key $k$) can create quantum states $S$ that anyone (in possession of public key $P$) can verify was issued by the bank without interacting with the bank, but nobody can spend twice?

Demi
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    @PaulUszak No – Ella Rose May 01 '18 at 02:18
  • @EllaRose Well I never. That's so cunning you could put a tail on it and call it a weasel. But what about the double spend problem? That paper is about simple verification against forgery, and only concerns national central banks. Spending genuine pounds in a sweet shop is entirely unrelated. And how can this money be transferred to the shop as only a central bank can actually create cash via monetary policy decisions. If ever there was too a broad question... Perhaps the question needs truncation? – Paul Uszak May 01 '18 at 03:17
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    @PaulUszak Double spending is impossible because duplicating the money is impractical, so if I give you some money, then you know I no longer have access to it (because it was physically transferred to you). Same as with physical cash. – Demi May 01 '18 at 03:20
  • @Demi Ah. The paper deals with authentication though doesn't it? It doesn't deal with ownership /transfer /conversion to-from paper. And what would you do with all the notes under my bed? A cashless authoritarian society? And do you realise that quantum thingies don't go down copper wires? And spending on board a plane /ship /submarine /car will be a right PITA. Recall how we all hate QKDNs? – Paul Uszak May 01 '18 at 03:39
  • And if you give (corporate) me your cash, I (as me) don't know one way or another if you gave it me as I work at the other end of the building /hemisphere. Tricky. – Paul Uszak May 01 '18 at 03:41
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    @PaulUszak I know. This is strictly of theoretical interest until we can store qbits indefinitely at negligible cost. And the intention is to replace physical cash, not electronic transfers. – Demi May 01 '18 at 20:49
  • @PaulUszak Imagine a future society that could make an atom-by-atom clone of anything, and could store qbits at negligible cost. No ordinary physical currency would be secure in such a world, but quantum currency could be. – Demi May 01 '18 at 20:51
  • @PaulUszak One key goal of such systems is that I can give you money and nobody whatsoever knows or is involved but you and I, just like with real-world cash. No electronic funds transfer scheme I know of has that property. – Demi May 01 '18 at 20:55
  • @PaulUszak We've been there before … twice. So, I'll just remind you with gentle warning while handling yet another rude/abusive flag with your name attached to it: *"please, remember to be nice"*. Thanks. – e-sushi May 02 '18 at 02:03
  • Comments are not for extended discussion; this conversation has been moved to chat. If you want to discuss this further, please use that chatroom to keep this comment section clean.. – e-sushi May 02 '18 at 02:09

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