The concept was first proposed by Stephen Wiesner circa 1970 (though it remained unpublished until 1983),[1] and later influenced the development of quantum key distribution protocols used in quantum cryptography.
[1] A formal proof of security, using techniques from semidefinite programming, was given in 2013.
[2] In addition to a unique serial number on each bank note (these notes are actually more like cheques, since a verification step with the bank is required for each transaction), there is a series of isolated two-state quantum systems.
Each of these is a two-state system in one of two bases: the horizontal basis has states with polarizations at 0° and 90° to the vertical, and the diagonal basis has states at 45° and 135° to the vertical.
On the bank note, the serial number is printed, but the polarizations are kept secret.
The fact that a quantum state cannot be copied is ultimately guaranteed by its proof by the no-cloning theorem, which underlies the security of this system.