Quantum solution to the Byzantine agreement problem - art. no. 217901

We present a solution to an old problem in distributed computing. In its si mplest form, a sender has to broadcast some information to two receivers, b ut they have access only to pairwise communication channels. Unlike quantum key distribution, here the goal is not secrecy but agreement, and the adve rsary (one of the receivers or the sender himself) is not outside but insid e the game. Using only classical channels this problem is provably impossib le. The solution uses pairwise quantum channels and entangled qutrits.