Active control of THz plasmon propagation in a one-dimensional electronic waveguide
Quantum nanoelectronics is pushing towards ever higher operating frequencies in order to realise quantum technologies capable of processing information at unprecedented speeds. A particularly promising direction is the development of flying electron qubits, which offer the prospect of quantum operations on picosecond timescales. Achieving in-flight quantum control in this regime would establish a fundamentally new paradigm for studying quantum entanglement and enable a novel form of quantum information processing based on propagating electronic wavepackets. Here we report a first step towards this goal by injecting ultrashort electron wavepackets into an engineered quantum nanoelectronic device. We demonstrate active control over the propagation speed of an electron wavepacket with a temporal duration as short as 4 ps in a quasi-one-dimensional electron waveguide with a length ranging from 10 $\mathrmμ$m to 40 $\mathrmμ$m. This advance provides a key building block for ultrafast quantum operations using flying electrons. Beyond its technological implications, our approach offers a platform for exploring the intrinsic dynamical processes that govern quantum transport and coherence in nanoscale electronic systems.