  We show that multi-mode entanglement of electrons in a mesoscopic conductor
can be detected by a measurement of the zero-frequency current correlations in
an electronic Hong-Ou-Mandel interferometer. By this mean, one can further
establish a lower bound to the entanglement of formation of two-electron input
states. Our results extend the work of Burkard and Loss [Phys. Rev. Lett. 91,
087903 (2003)] to many channels and provide a way to test the existence of
entangled states involving both orbital and spin degrees of freedom.
