"Quantum Blockchains Could Act Like Time Machines"

From IEEE Spectrum:

Quantum blockchain systems could resist hacks by quantum computers

A newly proposed "quantum blockchain" could lead to blockchain systems impervious from quantum-computer hacking, a new study finds.

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

A blockchain is a kind of 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 does not require a centralized institution to maintain its ongoing accuracy. The most well-known application of blockchains is Bitcoin, but a diverse array of startup companies, corporate alliances, and research projects have explored other potential uses for the technology.

"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.

However, blockchains might face trouble from another up-and-coming technology, quantum computers. Whereas classical computers switch transistors either on or off to symbolize data as ones and zeroes, 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. A powerful enough quantum computer could successfully break conventional cryptography, including that protecting blockchains. 

Now researchers in New Zealand suggest a quantum blockchain could resist hacking attempts from quantum computers. All the components of this system have already been experimentally realized, they add....

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