Quantum money underpinned by the mathematics of knots could be impossible to forge.

In a quantum monetary system, money is represented as a collection of quantum bits – qubits – on a quantum computer. There is a secret procedure for creating the money that only the authority in charge, such as a mint, can perform. And copying the quantum money is impossible thanks to a law of physics called the no-cloning theorem. Effectively, if someone learned enough information about the quantum money to duplicate …