Quantum correlation exists in any non-product state
  Simultaneous existence of correlation in complementary bases is a fundamental feature of quantum correlation, and we show that this characteristic is present in any non-product bipartite state. We propose a measure via mutually unbiased bases to study this feature of quantum correlation, and compare it with other measures of quantum correlation for several families of bipartite states. 
Yu Guo and Shengjun Wu
quant-ph math-ph math.MP