Mladen Pavicic

Mladen Pavicic

We consider attacks on two-way quantum key distribution protocols in which an undetectable eavesdropper copies all messages in the message mode. We show that under the attacks there is no disturbance in the message mode and that the mutual information between the sender and the receiver is always constant and equal to one. It follows that recent proofs of security for two-way protocols cannot be considered complete since they do not cover the considered attacks.

Mladen Pavicic, Oliver Benson, Andreas W. Schell et al.

Two-qubit quantum codes have been suggested to obtain better efficiency and higher loss tolerance in quantum key distribution. Here, we propose a two-qubit quantum key distribution protocol based on a mixed basis consisting of two Bell states and two states from the computational basis. All states can be generated from a single entangled photon pair resource by using local operations on only one auxiliary photon. Compared to other schemes it is also possible to deterministically discriminate all states using linear optics. Additionally, our protocol can be implemented with today's technology. When discussing the security of our protocol we find a much improved resistance against certain attacks as compared to the standard BB84 protocol.