  We 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 Luttinger
liquids paradigm.
