  We investigate the temperature and voltage dependence of the quantum
interference in an electronic Mach-Zehnder interferometer using edge channels
in the integer quantum-Hall-regime. The amplitude of the interference fringes
is significantly smaller than expected from theory; nevertheless the functional
dependence of the visibility on temperature and bias voltage agrees very well
with theoretical predictions. Superimposed on the Aharonov-Bohm (AB)
oscillations, a conductance oscillation with six times smaller period is
observed. The latter depends only on gate voltage and not on the AB-phase, and
may be related to single electron charging.
