Quantum cryptography using practical photonic systems

In future quantum information networks, where individual parties will have the ability to communicate in a variety of ways with trusted and untrusted parties, several cryptographic protocols, inherently linked to fundamental features of quantum mechanics, will become essential. Here, we are interested in protocols that are at the heart of many advanced secure communication tasks, namely key distribution and coin flipping. We examine the implementation of these protocols using photonic systems, which provide an ideal physical support for quantum communications. We discuss how imperfections and limitations of practical systems affect the security of the protocols and how implementations offering high performance and strong security guarantees – superior to what classical communication alone could ever provide – are nevertheless achieved. These results, together with perspectives for novel integrated photonic components, offer a powerful toolbox for practical applications of secure quantum communications.