Strong energy relaxation, dissipation and revival of quasiparticles propagating in an interacting quantum Hall liquid at $\nu=2$.

Coulomb interactions between neighboring edge channels of the quantum Hall effect can lead to energy relaxation. To explore this phenomenon, we have measured the energy distribution function of quasiparticles emitted at well-defined energy in an edge channel, at filling factor $\nu=2$. We show that, on sub-micron lengths, quasiparticles undergo a strong relaxation due to the second edge channel, with a survival probability dropping exponentially with their energy. Remarkably, this relaxation preserves the position and width of the quasiparticle peak in the energy distribution function. At intermediate lengths, we observe a marked revival of the peak at high injection energy. Despite the fact that our findings are qualitatively compatible with the conventionally considered theories, new ingredients such as dissipation seem crucial in order to provide a more quantitative comparison.