  We measure the average number of electrons loaded into an
electrostatically-defined quantum dot (QD) operated as a tunable-barrier
electron pump, using a point-contact (PC) charge sensor 1 micron away from the
QD. The measurement of the electron number probes the QD loading dynamics even
in the limit of slow gate voltage rise-times, when the pumped current is too
small to measure. Using simulations we show that, with optimised QD-PC
coupling, the experiment can make single-shot measurements of the number of
electrons in the QD with sufficiently high fidelity to test the error rate of
the electron pump with metrological precision.
