Circulant states with vanishing quantum discord
  We analyze a class of 2-qudit circulant states. They define generalization of well known 2-qubit X-states. We formula the necessary and sufficient criteria for vanishing quantum discord. We illustrate our analysis by an important subclass of circulant states -- so called Bell diagonal states. 
Bogna Bylicka, Dariusz Chru\'sci\'nski
quant-ph