Quantum Cryptography with Entangled Photons

In 2000 Thomas Jennewein and colleagues realized the first full implementation of entangled state quantum cryptography system in their laboratory.

The system based on polarization entangled photon pairs was able to establish highly secure keys by exploiting the inherent randomness of quantum measurements. The entangled photons were transmitted via optical fibers to Alice and Bob, who were separated by 360 m, where they were analyzed, detected and registered independently. After a measurement run the keys were established by Alice and Bob through classical communication over a standard computer network.

The 49984 bit large keys generated by the BB84 scheme were used to securely transmit an image of the “Venus von Willendorf” effigy. Alice encrypted the image via bitwise XOR operation with her key and transmitted the encrypted image to Bob via the computer network. Bob decrypted the image with his key, resulting in an image which showed only few errors due to the remaining bit error  in the keys.

Thomas Jennewein, Christoph Simon, Gregor Weihs, Harald Weinfurter, and Anton Zeilinger

Phys. Rev. Lett. 84, 4729 (2000)
www.arxiv.org/abs/quant-ph/9912117