Theory of Quantum Key Distribution: The Road Ahead (Invited Talk)

Abstract

Quantum Key Distribution (QKD) has been an area with lots of research activity. So nearly 25 years after the publication of the Bennett-Brassard 1984 protocol, what is left to do? As a basis of my talk, I will present the ideas of quantum key distribution in a language that emphasizes the common basis with information theoretic secure key distribution schemes that are based on independent noise assumptions in channels. As I will show, the role quantum theory plays is to verify the nature of correlations between sender, receiver and eavesdropper based only on the observations of sender and receiver. For reviews of practical QKD and issues addressed in this presentation, see [1,2,3].

Current research directions concentrate on the theoretic side on the optimal method of extracting secret key out of given observed correlations between sender and receiver. As it is the case in the classical scenario, different protocols using for example one-way or two-way communication over an authenticated public channel can have different maximum thresholds for error rates, and can yield different key rates. Other research directions deal with side channels and imperfections that are unavoidable in the implementation of the QKD protocols. After all, in implementations we are not sending ’qubits’, the quantum equivalent of classical bits, but real optical signals that have a rich internal structure.

As for applications, it is desirable to go beyond the simple point-to-point QKD connection and I will present research done within the European Consortium SECOQC [4] that builds a network demonstrator using trusted repeater stations in Vienna. This demonstrator involves the development of optical technology for the QKD implementation, but also the development of key management structures and routing protocols that are compatible with high-security application scenarios.