We report a method to characterize the potential barrier of a dynamic quantum dot by measuring the barrier height and determining the curvature. We show that the loading statistics and hence accuracy of electron transfer through the dynamic quantum dot depend significantly on these parameters, and hence our method provides a detailed characterization of device performance. This method takes a further step towards tunable barrier shapes, which would greatly increase the accuracy of single electron sources, allowing the single electron current to be useful for quantum sensing, quantum information, and metrology. We apply our method to the case of a tunable-barrier single-electron pump, an exemplary device that shows promise as a source of hot single electron wavepackets.
We note there was a discontinuity seen around T = 32 K, arising from a thermal cycle occurring to the device. On remeasuring the device, it was found δ1 was unchanged (ensuring consistency and generality of results) but the position in Vexit had slightly shifted by 14 mV. This has been accounted for in this analysis by offsetting curves for T < 32 K. Note that the curves of Figs. 1(c), 1(d), 2(a), and 3(a) are also offset.
The error bars plotted in Fig. 3(b) are the Type A (statistical) uncertainty, and these are used in the fit. The limit of our measurement resolution, and hence Type A uncertainty, is approximately 0.2 pA, which corresponds to , and points below this are not used in the fit. To show the crossover to the tunneling regime, we extend the fit curve in to this region.