Nonclassicality measures of single-mode quantum states

What is the most effective metric for quantifying the nonclassical characteristics of an individual quantum state? Our answer to this question is that it depends on what will be used for. Here we present some of the most widely used measures, as well as some promising ones. In this discussion, we analyze the question and ultimately determine that there is no singular superior metric. However, a mix of measures can provide a comprehensive understanding of the situation. Each measure has a potential application, some can be classified as a general nonclassicality measure, while others are dedicated measures. Some measures have a practical physical meaning, while others are justified by the results. We show that the negativity of the Wigner function, Mandel’s Q parameter and Hilbert–Schmidt distance are good dedicated measures, while Roughness is a general one, like Skewness in this case for pure states.