  We show how the spin independent scattering between two identical flying
qubits can be used to implement an entangling quantum gate between them. We
consider one dimensional models with a delta interaction in which the qubits
undergoing the collision are distinctly labeled by their opposite momenta. The
logical states of the qubit may either be two distinct spin (or other internal)
states of a fermion or a boson or two distinct momenta magnitudes of a spinless
boson. Our scheme could be added to linear optics-like quantum information
processing to enhance its efficiency, and can also aid the scaling of quantum
computers based on static qubits without resorting to photons. Three distinct
ingredients -- the quantum indistinguishability of the qubits, their
interaction, and their dimensional confinement, come together in a natural way
to enable the quantum gate.
