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Quantum Digital Signatures without quantum memory

Quantum Digital Signatures (QDS) allow for the exchange of messages from one sender to multiple recipients, with the guarantee that messages cannot be forged or tampered with. Additionally, messages cannot be repudiated -- if one recipient accepts a message, she is guaranteed that others will accept the same message as well. While messaging with these types of security guarantees are routinely performed in the modern digital world, current technologies only offer security under computational assumptions. QDS, on the other hand, offer security guaranteed by quantum mechanics. All thus far proposed variants of QDS require long-term, high quality storage of quantum information, making them unfeasible in the foreseeable future. Here, we present the first QDS scheme where no quantum memory is required, and all quantum information processing can be performed using just linear optics. This makes QDS feasible with current technology.