Single-electron pumps based on isolated impurity atoms have recently been experimentally demonstrated. In these devices the Coulomb potential of an atom creates a localised electron state with a large charging energy and considerable orbital level spacings, enabling robust charge capturing processes. In these single-atom pumps, the confinement potential is hardly affected by the periodic driving of the system. This is in contrast to the often used gate-defined quantum dot pumps, for which a strongly time-dependent potential leads to significantly different charge pumping processes. Here we describe the behaviour and the performance of an atomic, single parameter, electron pump. This is done by considering the loading, isolating and unloading of one electron at the time, on a phosphorous atom embedded in a silicon double gate transistor. The most important feature of the atom pump is its very isolated ground state, which can be populated through the fast loading of much higher lying excited states and a subsequent fast relaxation proces. This leads to a substantial increase in pumping accuracy, and is opposed to the adverse role of excited states as observed for quantum dot pumps due to non-adiabatic excitations. The pumping performances are investigated as a function of dopant position, revealing a pumping behaviour robust against the expected variability in atomic position.
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