  We consider a mesoscopic circuit in the quantum Hall effect regime comprising
two synchronized single-particle sources emitting particles into a Mach-Zehnder
interferometer. While particles from one source can possibly interfere at the
interferometer output, particles from the second source are injected directly
into one of the interferometer's arms and are used to create tunable and
coherent suppression of interference. If particles from the two different
sources collide at the interferometer output the magnetic-flux dependence of
the charge transferred to one of the output contacts is suppressed. In contrast
the interference pattern in the current at a fixed time is preserved and the
impact of the second source manifests itself in a time-dependent phase-shift.
