  One of the most fascinating challenges in Physics is the realization of an
electron-based counterpart of quantum optics, which requires the capability to
generate and control single electron wave packets. The edge states of quantum
spin Hall (QSH) systems, i.e. two-dimensional (2D) topological insulators
realized in HgTe/CdTe and InAs/GaSb quantum wells, may turn the tide in the
field, as they do not require the magnetic field that limits the
implementations based on quantum Hall effect. Here we show that an electric
pulse, localized in space and/or time and applied at a QSH edge, can
photoexcite electron wavepackets by intra-branch electrical transitions,
without invoking the bulk states or the Zeeman coupling. Such wavepackets are
spin-polarised and propagate in opposite directions, with a density profile
that is independent of the initial equilibrium temperature and that does not
exhibit dispersion, as a result of the linearity of the spectrum and of the
chiral anomaly characterising massless Dirac electrons. We also investigate the
photoexcited energy distribution and show how, under appropriate circumstances,
minimal excitations (Levitons) are generated. Furthermore, we show that the
presence of a Rashba spin-orbit coupling can be exploited to tailor the shape
of photoexcited wavepackets. Possible experimental realizations are also
discussed.
