  Electron quantum optics explores the coherent propagation and interference of
single-electron charge pulses in electronic nanoscale circuits that are similar
to table-top setups with photons. So far, experiments with dynamic
single-electron emitters have focused on normal-state conductors, however, the
inclusion of superconductors would pave the way for a wide range of
applications that exploit the electron-hole degree of freedom, for example, for
quantum information processing or quantum sensing. Here, we propose and analyze
a tunable mechanism for the on-demand conversion of single-electron pulses into
holes through Andreev processes on a superconductor. To this end, we develop a
Floquet-Nambu scattering formalism that allows us to describe the dynamic
conversion of charge pulses on a superconductor, and we show that it is
possible to generate arbitrary superpositions of electrons and holes with the
degree of mixing controlled by the magnetic flux in an interferometric setup.
We provide a detailed discussion of the optimal operating conditions in
realistic situations and demonstrate that our proposal is feasible based on
current technology.
