Activity: Talk or presentation › Oral presentation
Secure communication requires a secret key for encryption and decryption. Quantum Key Distribution (QKD) utilizes the quantum nature of light for on-the-fly generation of a secret key between distant parties. The security of this method is based on the no-cloning theorem, which forbids copying quantum states. The standard implementation of the BB84 protocol uses the two-dimensional polarization basis to encode information in photons. Therefore the alphabet contains only two symbols: "0" and "1", limiting the information content per photon to 1 bit. This is a bottleneck especially for encrypted video communication. We encode information in 4096 distinct spatial positions of a photon, which increases the dimensionality and the information content to 8 bit per photon and provides better security. The 2nd, mutually unbiased basis required for QKD is realized as the Fourier transform of the spatial basis. We experimentally demonstrate an information content of over 8 bit per sifted photon and discuss the security of our method.