  We consider transport properties of a single edge of a two-dimensional
topological insulators, in presence of Rashba spin-orbit coupling, driven by
two external time-dependent voltages and connected to a thin superconductor. We
focus on the case of a train of Lorentzian-shaped pulses, which are known to
generate coherent single-electron excitations in two-dimensional electron gas,
and prove that they are minimal excitations for charge transport also in
helical edge states, even in the presence of spin-orbit interaction.
Importantly, these properties of Lorentzian-shaped pulses can be tested
computing charge noise generated by the scattering of particles at the thin
superconductor. This represents a novel setup where electron quantum optics
experiments with helical states can be implemented, with the superconducting
contact as an effective beamsplitter. By elaborating on this configuration, we
also evaluate charge noise in a collisional Hong-Ou-Mandel configuration,
showing that, due to the peculiar effects induced by Rashba interaction, a
non-vanishing dip at zero delay appears.
