Quantum money is a form of currency that employs the strange laws of quantum mechanics to ensure that it cannot be copied but at the same time can be easily verified. These properties make it an ideal medium of exchange, just like ordinary cash, but without any risk of counterfeiting.
The idea was first developed by the physicist Stephen Wiesner in 1970 using the notion that any attempt to measure an unknown quantum state inevitably destroys it. By comparison, the process of measuring a known quantum state preserves it.
Wiesner realized that if the details of the quantum state were kept secret, by a central bank for example, this property could be used to guarantee the veracity of quantum money while ensuring it could never be copied.
