Quantum Blockchains Could Act Like Time Machines

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.

Source: ieee.org