  A qubit (a spin-1/2 particle) prepared in the up state is scattered by local
spin-flipping potentials produced by the two target qubits (two fixed spins),
both prepared in the down state, to generate an entangled state in the latter
when the former is found in the down state after scattering. The scattering
process is analyzed in three dimensions, both to lowest order and in full order
in perturbation, with an appropriate renormalization for the latter. The
entanglement is evaluated in terms of the concurrence as a function of the
incident and scattering angles, the size of the incident wave packet, and the
detector resolution, to clarify the key elements for obtaining an entanglement
with high quality. The characteristics of the results are also discussed in the
context of (in)distinguishability of alternative paths for a quantum particle.
