  We consider the phase-coherent transport of electrons passing through an
Aharonov-Bohm ring while interacting with a tunnel charge in a double quantum
dot (representing a charge qubit) which couples symmetrically to both arms of
the ring. For Aharonov-Bohm flux Phi_AB=h/2e we find that electrons can only be
transmitted when they flip the charge qubit's pseudospin parity an odd number
of times. The perfect correlations of the dynamics of the pseudospin and
individual electronic transmission and reflection events can be used to
entangle the charge qubit with an individual passing electron.
