The digital currency Bitcoin has had remarkable growth since it was firstproposed in 2008. Its distributed nature allows currency transactions without acentral authority by using cryptographic methods and a data structure calledthe blockchain. In this paper we use the no-cloning theorem of quantummechanics to introduce Quantum Bitcoin, a Bitcoin-like currency that runs on aquantum computer. We show that our construction of quantum shards and twoblockchains allows untrusted peers to mint quantum money without risking theintegrity of the currency. The Quantum Bitcoin protocol has several advantagesover classical Bitcoin, including immediate local verification of transactions.This is a major improvement since we no longer need the computationallyintensive and time-consuming method Bitcoin uses to record all transactions inthe blockchain. Instead, Quantum Bitcoin only records newly minted currencywhich drastically reduces the footprint and increases efficiency. We presentformal security proofs for counterfeiting resistance and show that a quantumbitcoin can be re-used a large number of times before wearing out - just likeordinary coins and banknotes. Quantum Bitcoin is the first distributed quantummoney system and we show that the lack of a paper trail implies full anonymityfor the users. In addition, there are no transaction fees and the system canscale to any transaction volume.
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