  The work is motivated by the puzzling results of the recent experiment [S.
Tewari et al., Phys. Rev. B 93, 035420 (2016)], where a robust coherence
recovery from a certain energy was detected for an electron injected into the
quantum Hall edge at the filling factor 2. After passing through a quantum dot
the electron then tunnels into the edge with a subsequent propagation towards a
symmetric Mach-Zender interferometer, after which the visibility of
Aharonov-Bohm (AB) oscillations is measured. According to conventional
understanding its decay with the increasing energy of the injected electron was
expected, which was confirmed theoretically in the bosonization framework. Here
we analyze why such a model fails to account for the coherence recovery and
show that the reason is essentially the destructive interference of the two
quasiparticles (charge and neutral modes) forming at the edge out of the
incoming electron. This statement is robust with respect to the strength of
Coulomb interaction. We firstly exploit the idea of introducing an imbalance
between the quasiparticles, by creating different conditions of propagation for
them. It can be done by taking into account either dispersion or dissipation,
which indeed results in the partial coherence recovery. The idea of imbalance
can also be realized by applying a periodic potential to the arms of
interferometer. We discuss such an experiment, which might also shed light on
the internal coherence of the two edge excitations. Another scenario relies on
the lowering of the energy density of the electron wave packet by the time it
arrives at the interferometer in presence of dissipation or dispersion. This
energy density is defined by a certain parameter, which is completely
independent of the injected energy, which naturally explains the emergence of a
threshold energy in the experiment.
