We propose a measure of non-classical correlations in bipartite quantumstates based on local unitary operations. We prove the measure is non-zero ifand only if the quantum discord is non-zero; this is achieved via a newcharacterization of zero discord states in terms of the state's correlationmatrix. Moreover, our scheme can be extended to ensure the same relationshipholds even with a generalized version of quantum discord in which higher-rankprojective measurements are allowed. We next derive a closed form expressionfor our scheme in the cases of Werner states and (2 x N)-dimensional systems.The latter reveals that for (2 x N)-dimensional states, our measure reduces tothe geometric discord [Dakic et al., PRL 105, 2010]. A connection to the CHSHinequality is shown. We close with a characterization of all maximallynon-classical, yet separable, (2 x N)-dimensional states of rank at most two(with respect to our measure).
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机译：我们提出了一种基于局部unit运算的二分量子态中非经典相关性的度量。当且仅当量子失调不为零时，我们证明测度为非零。这是通过根据状态的相关矩阵对零不和谐状态进行重新表征来实现的。此外，我们的方案可以扩展以确保相同的关系保持，即使使用允许更高等级投影测量的广义量子不和谐式。接下来，我们在Werner态和（2 x N）维系统的情况下为我们的方案导出一个封闭形式的表达式。后者揭示了对于（2 x N）维状态，我们的测度减少到几何不和谐[Dakic等。 ，PRL 105，2010]。显示了与CHSHinequality的连接。最后，我们对所有最大非经典但可分离的（2 x N）维等级状态（最多2个相对于我们的度量）进行表征。
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