  Recent experiments have shown that the edge states of a quantum Hall sample
can be coupled to a superconductor, so that incoming electrons in the edge
states can be Andreev converted on the superconductor as coherent
superpositions of an electron and a hole. In addition to this, single-electron
emitters that operate in the gigahertz regime have been realized. Motivated by
this remarkable experimental progress, we here analyze the Andreev reflections
of incoming charge pulses on the interface with a superconductor. To this end,
we employ a Wigner function representation that allows us to visualize the
response function of the interface both in the time and in the frequency
domain. We analyze the response of an interface between a normal-metal and a
singlet or triplet superconductor with and without an insulating barrier in
between them. As a special case, we analyze the Andreev reflections of clean
single-particle excitations that are generated by the application of
lorentzian-shaped voltage pulses to the contacts of the inputs. Our predictions
may be tested in future experiments with edge states coupled to
superconductors.
