  We propose and analyze a mesoscopic device producing on-demand entangled
pairs of electrons. The system consists of two capacitively coupled
Mach-Zehnder interferometers implemented in a quantum Hall structure. A pair of
electron wave-packets is injected into the chiral edge states of two (of the
four) incoming arms; scattering on the incoming interferometers splits the
wave-packets into four components of which two interact. The resulting
interaction phase associated with this component leads to the entanglement of
the state; the latter is scattered at the outgoing beam splitter and analyzed
in a Bell violation test measuring the presence of particles in the four
outgoing leads. We study the two-particle case and determine the conditions to
reach and observe full entanglement. We extend our two-particle analysis to
include the underlying Fermi seas in the quantum Hall device; the change in
shape of the wave-function, the generation of electron-hole pairs in the
interaction regime, and a time delay between the pulses all reduce the degree
of visible entanglement and the violation of the Bell inequality, effects which
we analyze quantitatively. We determine the device settings optimizing the
entanglement and the Bell test and find that violation is still possible in the
presence of the Fermi seas, with a maximal Bell parameter reaching ${\cal B} =
2.18 > 2$ in our setup.
