Quantum Hall edge channels at integer filling factor provide a unique test-bench to understand decoherence and relaxation of single electronic excitations in a ballistic quantum conductor. In this Letter, we obtain a full visualization of the decoherence scenario of energy (Landau) and time (Levitov) resolved single electron excitations at filling factor ν = 2. We show that the Landau excitation exhibits a fast relaxation followed by spin-charge separation whereas the Levitov excitation only experiences spin-charge separation. We finally suggest to use Hong-Ou-Mandel type experiments to probe specific signatures of these different scenarios.PACS numbers: 71.10.Pm, 73.43.Lp The recent demonstration of on-demand single electron sources able to inject single electronic excitations into quantum Hall edge channels 1-3 or 2DEG 4,5 has opened a new era of quantum coherent electronics. By combining these sources to electronic beam splitters, experiments analogous to the celebrated Hanbury-Brown and Twiss and Hong-Ou-Mandel 6 experiments have been demonstrated at the single electron level 7,8 thus opening the way to electron quantum optics 9,10 . However, this emerging field goes beyond a simple analogy with photon quantum optics: first of all, the Fermi statistics of electrons differs from the Bose statistics of photons and leads to the Fermi sea, a state with no analogue in photon quantum optics. Moreover, electrically charged electrons experience Coulomb interactions which, despite screening, are expected to induce strong decoherence effects as demonstrated by Mach-Zehnder interferometry experiments [11][12][13][14][15] . Moreover, an in-depth study of the relaxation of a non-equilibrium electronic distribution at filling factor ν = 2 has shown that a description of the quantum Hall edge channels in terms of Landau quasiparticle excitations is not valid 16,17 .Although the above results on single electron relaxation and decoherence have been obtained by considering stationary sources and time averaged quantities such as the electron distribution function, the recent demonstration of the electronic Hong-Ou-Mandel (HOM) experiment 8 calls for a time resolved approach to single electron coherence taking into account the finite duration of the electronic excitation. The aim of this Letter is precisely to discuss the decoherence scenario of two single electron excitations emitted by state of the art sources. First, the Landau quasi-particles correspond to a Lorentzian wave packet in energy emitted by a properly operated quantum dot 1 . Secondly, the Levitov quasi-particles or Levitons 4 are the minimal single electron state obtained by applying a Lorentzian time-dependent potential with quantized flux 18 . We show that comparing the real time aspects of their decoherence brings a better understanding of the underlying mechanisms of electronic decoherence whose specific features could be experimentally tested in HOM experiments.Recently, finite frequency admittance measurements have demonstrated the existence of collecti...

International audienceWe study the decoherence and relaxation of a single elementary electronic excitation propagating in a one-dimensional chiral conductor. Using two-particle interferences in the electronic analog of the Hong-Ou-Mandel experiment, we analyze quantitatively the decoherence scenario of a single electron propagating along a quantum Hall edge channel at filling factor 2. The decoherence results from the emergence of collective neutral excitations induced by Coulomb interaction and leading, in one dimension, to the destruction of the elementary quasiparticle. This study establishes the relevance of electron quantum optics setups to provide stringent tests of strong interaction effects in one-dimensional conductors described by the Luttinger liquids paradigm