  Electron flying qubits are envisioned as potential information link within a
quantum computer, but also promise -- alike photonic approaches -- a
self-standing quantum processing unit. In contrast to its photonic counterpart,
electron-quantum-optics implementations are subject to Coulomb interaction,
which provide a direct route to entangle the orbital or spin degree of freedom.
However, the controlled interaction of flying electrons at the single particle
level has not yet been established experimentally. Here we report antibunching
of a pair of single electrons that is synchronously shuttled through a circuit
of coupled quantum rails by means of a surface acoustic wave. The in-flight
partitioning process exhibits a reciprocal gating effect which allows us to
ascribe the observed repulsion predominantly to Coulomb interaction. Our
single-shot experiment marks an important milestone on the route to realise a
controlled-phase gate for in-flight quantum manipulations.
