Fig. 2: Local control of the number of transmitting electron conduction channels in 100 μm quantum wire.

Time-resolved measurement of plasmon wavepackets excited by 52 ps-long voltage pulse (a) and 500 ps-long voltage pulse (b) for different voltages on the gates of QPC1. The amplitude is normalised to one. Each curve is offset vertically for clarity. The gate voltage V_QPC1 was stepped from  −0.2 V at the bottom to  − 1.4 V at the top. The gate voltage V_w1,w2 was fixed to  − 0.7 V. The peak position is indicated by the black circles. The shape of the voltage pulse used to excite the plasmon wavepacket is drawn by the black dashed line. c. Speed of the plasmon wavepackets calculated from the peak delay indicated by the black circles in (a, b). Here the number N on top of the grey shaded gate voltage indicates the number of transmitting electron channels across QPC1 at each voltage, which is determined by the observation of the quantised conductance.