One of the biggest concerns of blockchain developers, is what happens when quantum computers become a viable alternative to modern computers? In theory, their computing power could invalidate the encryption that secures blockchains from tampering. One intriguing solution suggests leveraging quantum mechanics to protect the blockchain from quantum computers.

　　Blockchain technology is far from easy to get your head around. We have an in-depth guide that explains it, but in a nutshell, it’s a digital ledger which uses encryption to validate new entries and protect old ones. It’s most common use is as the backbone of cryptocurrencies like Bitcoin, but it’s also found use in government systems and board gaming tablets.

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　　One of its biggest potential problems in the future though, is that the sheer power of a quantum computer could easily break the blockchain’s encryption safeguards, giving the computer’s owner control over a blockchain’s past and future.

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　　While quantum computers aren’t yet viable in such a scenario, they will be in the future, which is why researchers like Del Rajan have been devising potential solutions. In a paper co-authored with Matt Visser, a fellow physicist at Victoria University of Wellington in New Zealand, the pair propose a blockchain that leverages quantum entanglement — the practice of linking two or more particles together. When entangled, each particle can influence the other simultaneously, no matter the distance between them.

　　Where traditional entanglement bridges vast distances to send information though, Rajan and Visser’s paper suggests entangling across time instead. They propose encoding the blockchain into quantum entangled photons, the most recent of which is summarily absorbed by the next one in the blockchain. In theory, this should make it possible to validate transactions, while preventing alterations to the blockchain, since the original entangled photon does not exist anymore.

　　Although the possibility would still exist for a hacker with massive quantum computing power to manipulate the latest photon (block), that would only invalidate that one block, making it obvious that a hack too place. Crucially though, they wouldn’t be able to tamper with the rest of the blockchain.

　　All of this exists in theory at the moment, though the two paper’s authors note that each component of the idea has been realized in experimental scenarios.

　　Perhaps the most intriguing claim of the whole paper though, is that such a system could be viewed in some measure as a “quantum networked time machine,” as Spectrum highlights.