The world’s first Quantum blockchain is a “quantum time machine”

A newly proposed Quantum Blockchain, which at first glance loosely resembles the Quantum Safe Blockchain a team in Russia recently created, could lead to blockchain systems “impervious from quantum computer hacking,” a new study finds.

Weirdly the new quantum blockchain can be interpreted as influencing its own past, making it behave like a time machine, the researchers added.

A blockchain is a kind of distributed database that holds records about the past, such as a history of financial or other transactions, that every node in the network can agree on and that doesn’t require a centralised, third party institution to maintain its ongoing accuracy. The most well known application of blockchains is Bitcoin, but it’s also the technology that’s now behind transforming the global financial system and global supply chains, and much more.

"It's expected that 10 percent of global GDP could be stored on blockchain technology by 2027," says lead author Del Rajan, a theoretical physicist at Victoria University of Wellington in New Zealand who led the project.

However, blockchains might face trouble from another up and coming technology, quantum computers. Whereas classical computers switch their transistors either on or off to symbolise data as binary 1’s and 0’s, quantum computers use quantum bits or “Qubits” that, because of the surreal nature of quantum physics, can be in a state of superposition where they are both 1 and 0 simultaneously.

Superposition lets one qubit perform two calculations at once, and if two qubits are linked through a quantum effect known as entanglement, they can help perform 2^2 or four calculations simultaneously; three qubits, 2^3 or eight calculations; and so on. In principle, a quantum computer with 300 qubits could perform more calculations in an instant than there are atoms in the visible universe, and a powerful enough quantum computer could successfully break at least 70 percent of all of today’s popular encryption technologies, and that includes the encryption that protects today’s blockchains.

The researchers in New Zealand suggest a quantum blockchain could resist such hacking attempts from quantum computers, and add that everything needed to protect tomorrow’s blockchains from attack are already here.

"Previous blockchains that worked with quantum operations were presented, but the blockchain itself was never quantum," said Rajan, “we are presenting the world's first fully quantum blockchain."

Although I think the Russians I mentioned earlier might take umbrage at that statement… but let’s let them sort that out between themselves.

Quantum blockchains in theory rely on entanglement. When two or more particles such as photons get entangled, they can influence each other simultaneously no matter how far apart they are, a phenomenon Einstein dubbed "Spooky action at a distance."

Quantum computers and other quantum technologies usually rely on entanglement across space, but the teams new quantum blockchain depends on entanglement in time instead, that is, linking two or more particles no matter how far apart they are in time. Yes I know, entanglement across time is a weird concept but lots of stuff today is weird, like your cat, so just nod your head and let’s move on…

Conventional blockchains organise records into blocks of data which encryption technologies link together in chronological order. If a hacker attempts to tamper with a particular block, the encryption is designed to invalidate all future blocks following the tampered block.

In the quantum blockchain, however, the records in a block are encoded into a series of photons that are entangled with each other. These blocks are linked in chronological order through entanglement in time.

As the blocks making up a quantum blockchain are transferred within a network of quantum computers, photons encoding each block get created and then absorbed by the nodes making up the network. However, entanglement links these photons across time, even photons that never existed at the same time.

"Records about past transactions are encoded onto a quantum state that is spread across time," said Rajan.

In this scenario, a hacker can’t tamper with any of the photons that are being used to encode records from the past since those photons no longer exist in the current time – they’ve already gotten absorbed. At best, a hacker can attempt to tamper with the most recent photon, the most current block, and successfully doing so would invalidate that block, informing others it got hacked.

"This is more desirable than the standard case where an attacker has the ability, in principle, to tamper with any block," said Rajan.

The researchers say with entanglement in time, measuring the last photon in a block influences the first photon of that block in the past before it got measured. Essentially, current records in a quantum blockchain are not merely linked to a record of the past, but rather a record in the past, one does that not exist anymore.

"This work can be viewed as a quantum time machine," says senior author Matt Visser, a theoretical physicist at the Victoria University of Wellington. Rajan and Visser detailed their findings in a paper online in April.