  A scattering approach to entanglement in mesoscopic conductors with
independent fermionic quasiparticles is discussed. We focus on conductors in
the tunneling limit, where a redefinition of the quasiparticle vacuum
transforms the wavefunction from a manybody product state of noninteracting
particles to a state describing entangled two-particle excitations out of the
new vacuum. The approach is illustrated with two examples (i) a
normal-superconducting system, where the transformation is made between
Bogoliubov-de Gennes quasiparticles and Cooper pairs, and (ii) a normal system,
where the transformation is made between electron quasiparticles and
electron-hole pairs. This is compared to a scheme where an effective
two-particle state is derived from the manybody scattering state by a reduced
density matrix approach.
