Quantum security for your credit card

Among the many unusual features that distinguish quantum mechanics from classical mechanics is the “no-cloning” theorem: It is impossible to perfectly replicate an unknown quantum state (see the Quick Study by Bill Wootters and Wojciech Zurek, Physics Today, February 2009, page 76). Quantum cryptography aims to exploit that property in order to keep communications secure from would-be eavesdroppers (see the article by Daniel Gottesman and Hoi-Kwong Lo, Physics Today, November 2000, page 22). Now Pepijn Pinkse and colleagues at the University of Twente and the Eindhoven University of Technology have shown how to provide fraud-proof physical identification using quantum-secure authentication (QSA). The keys for their experiment were thin layers of white paint sprayed onto the “cards” to be authenticated. When a light pulse comprising only a few photons is focused onto a key, the pattern of reflected light depends sensitively on the spatial shape of the...