Robustness of a quantum key distribution with two and three mutually   unbiased bases
  We study the robustness of various protocols for quantum key distribution. We first consider the case of qutrits and study quantum protocols that employ two and three mutually unbiased bases. We then derive the optimal eavesdropping strategy for two mutually unbiased bases in dimension four and generalize the result to a quantum key distribution protocol that uses two mutually unbiased bases in arbitrary finite dimension. 
Filippo Caruso, Helle Bechmann-Pasquinucci and Chiara Macchiavello