Date Added: Dec 2009
Public-key quantum money is a cryptographic protocol in which a bank can create quantum states which anyone can verify, but no one except possibly the bank can clone or forge. There are no secure public-key quantum money schemes in the literature; as the authors show in this paper, the only previously published scheme is insecure. They introduce a category of quantum money protocols which they call collision-free. For these protocols, even the bank cannot prepare multiple identical-looking pieces of quantum money. They present a blueprint for how such a protocol might work as well as a concrete example which they believe may be insecure.