  We consider the violation of the Leggett-Garg inequality in electronic
Mach-Zehnder inteferometers. This set-up has two distinct advantages over
earlier quantum-transport proposals: firstly, the required correlation
functions can be obtained without time-resolved measurements. Secondly, the
geometry of an interferometer allows one to construct the correlation functions
from ideal negative measurements, which addresses the non-invasiveness
requirement of the Leggett-Garg inequality. We discuss two concrete
realisations of these ideas: the first in quantum Hall edge-channels, the
second in a double quantum dot interferometer.
