  We consider the electronic analog of the quantum optics Hong-Ou-Mandel
interferometer, in a realistic condensed matter device based on single electron
emission in chiral edge states. For electron-electron collisions, we show that
the measurement of the zero-frequency current correlations at the output of a
quantum point contact produces a dip giving precious information on the
electronic wavepackets and coherence. As a feature truly unique to Fermi
statistics and condensed matter, we show that two-particle interferences
between electron and hole in the Fermi sea can produce a positive peak in the
current correlations, which we study for realistic experimental parameters.
