  We study the evolution of a single-electron packet of Lorentzian shape along
an edge of the integer quantum Hall regime or in a Mach-Zehnder interferometer,
considering a capacitive Coulomb interaction and using a bosonization approach.
When the packet propagates along a chiral quantum Hall edge, we find that its
electron density profile becomes more distorted from Lorentzian due to the
generation of electron-hole excitations, as the interaction strength increases
yet stays in a weak interaction regime. However, as the interaction strength
becomes larger and enters a strong interaction regime, the distortion becomes
weaker and eventually the Lorentzian packet shape is recovered. The recovery of
the packet shape leads to an interesting feature of the interference visibility
of the symmetric Mach-Zehnder interferometer whose two arms have the same
interaction strength. As the interaction strength increases, the visibility
decreases from the maximum value in the weak interaction regime, and then
increases to the maximum value in the strong interaction regime. We argue that
this counterintuitive result also occurs under other types of interactions.
