Quantifying quantum coherence and the deviation from the total probability formula

We propose a novel approach to quantify quantum coherence which, contrary to the previous ones, does not rely on resource theory but rather on ontological considerations. In this framework, coherence is understood as the ability of a quantum system’s statistics to deviate from the total probability formula. After motivating the importance of the total probability formula in quantum foundations, we propose a new set of axioms that a measure of coherence should satisfy, and show that it defines a class of measures different from the main previous proposal. Finally, we prove a general result about the dependence of the [Formula: see text]-coherence norm on the basis of interest, and show that it is well approximated by the square root of the purity in most bases.