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

Photoexcitation in two-dimensional topological insulators: Generating and controlling electron wavepackets in Quantum Spin Hall systems