  We present two entanglement concentration protocols (ECPs) for arbitrary
three-electron W state based on their charges and spins. Different from other
ECPs, in both two ECPs, with the help of the electronic polarization beam
splitter (PBS) and charge detection, the less-entangled W state can be
concentrated into a maximally entangled state only with some single charge
qubits. The second ECP is more optimal than the first one, for by constructing
the complete parity check gate, the second ECP can be used repeatedly to
further concentrate the less-entangled state and obtain a higher success
probability. Therefore, both the ECPs, especially the second one may be useful
in current quantum information processing.
