  Single-electron sources are an essential component of modern quantum
nanoelectronic devices. Owing to their high accuracy and stability, they have
been successfully employed for metrology applications, studying fundamental
matter interactions and more recently for electron quantum optics. They are
traditionally driven by state-of-the-art arbitrary waveform generators that are
capable of producing single-electron pulses in the sub-100 ps timescale. In
this work, we use an alternative approach for generating ultrashort electron
wavepackets. By combining several harmonics provided by a frequency comb, we
synthesise Lorentzian voltage pulses and then use them to generate electron
wavepackets. Through this technique, we report on the generation and detection
of an electron wavepacket with temporal duration of 27 ps generated on top of
the Fermi sea of a 2-dimensional electron gas - the shortest reported to date.
Electron pulses this short enable studies on elusive, ultrafast fundamental
quantum dynamics in nanoelectronic systems and pave the way to implement flying
electron qubits by means of Levitons.
