  A Josephson junction may be driven through a transition where the
superconducting condensate favors an odd over an even number of electrons. At
this switch in the ground-state fermion parity, an Andreev bound state crosses
through the Fermi level, producing a zero-mode that can be probed by a point
contact to a grounded metal. We calculate the time-dependent charge transfer
between superconductor and metal for a linear sweep through the transition. One
single quasiparticle is exchanged with charge $Q$ depending on the coupling
energies $\gamma_1,\gamma_2$ of the metal to the Majorana operators of the
zero-mode. For a single-channel point contact, $Q$ equals the electron charge
$e$ in the adiabatic limit of slow driving, while in the opposite quenched
limit $Q=2e\sqrt{\gamma_1\gamma_2}/(\gamma_1+\gamma_2)$ varies between $0$ and
$e$. This provides a method to produce single charge-neutral quasiparticles on
demand.
