We consider maximal violations of the Leggett-Garg inequality, obtained by maximizing over all possible measurement operators, in relation to nonunitary aspects of the system dynamics. We model the action of an environment on a qubit in terms of generic quantum channels and relate the maximal value of the Leggett-Garg correlator to the channel parameters. We focus on unital channels and hence on decoherence. In certain important cases, exact relations between the channel parameters and maximal violations can be found. Moreover, we demonstrate the existence of distinct thresholds for the channel parameters, below which no violation of the Leggett-Garg inequality can occur.

• Received 16 December 2012

DOI:https://doi.org/10.1103/PhysRevA.87.032106