No abstract

Controlled charge pumping in an AlGaAs/GaAs gated nanowire by single-parameter modulation is studied experimentally and theoretically. Transfer of integral multiples of the elementary charge per modulation cycle is clearly demonstrated. A simple theoretical model shows that such a quantized current can be generated via loading and unloading of a dynamic quasi-bound state. It demonstrates that non-adiabatic blockade of unwanted tunnel events can obliterate the requirement of having at least two phase-shifted periodic signals to realize quantized pumping. The simple configuration without multiple pumping signals might find wide application in metrological experiments and quantum electronics.PACS numbers: 73.23.Hk,73.22.Dj,73.63.Kv An important milestone in the study of single electron transport is the closure of the quantum metrological triangle for frequency, dc current, and dc voltage [1]. Dc voltage is currently realized from the frequency standard through the Josephson effect. Dc current can then be derived using the quantum Hall effect. Direct realization of dc current from frequency is the currently missing side of the triangle. The closure of the quantum metrological triangle provides a test whether the fundamental constants really appear the same in these different systems [2]. The results of this kind of experiment will also impact on a future system of units which might be based on fundamental constants [3].A current source relevant for the above experiments must produce at least nanoampere currents to be measurable with sufficient accuracy. The electron pump based on arrays of Coulomb blockaded quantum dots (see [4] for a review) or quantum interference [2,5,6] is one class of devices being investigated with respect to metrological relevance [7,8,9]. Electron pumps are typically driven by multiple radio frequency (rf) signals with a well maintained phase relationship, producing a quantized current, i.e. limited to certain values according to I = −nef (with n = 1, 2, 3 . . . , e the negative elementary charge and f the driving frequency). Usually, the accuracy in I degrades with increasing f , which has so far prevented the generation of sufficiently accurate nanoampere currents. An alternative, but challenging task would be the parallelization of pumps driven at intermediate frequencies. Here, pumps requiring only a single rf signal would fundamentally reduce the complexity in the parallelization of such devices. However, electron pumps driven by only one gate [10,11,12,13] have so far not experimentally demonstrated the generation of quantized current. In addition, most models of quantized pumping [5,6,14,15,16,17] have assumed at least two parameters modulated out phase, which may be motivated by the fact that in the adiabatic limit a single periodic perturbation cannot determine the direction of the current [18].In this paper we address this issue and report on the first experimental realization of quantized charge pumping in which only one gate is modulated. We demonstrate on a transparent quantu...

We present experimental results of high-frequency quantized charge pumping through a quantum dot formed by the electric field arising from applied voltages in a GaAs/AlGaAs system in the presence of a perpendicular magnetic field B. Clear changes are observed in the quantized current plateaus as a function of applied magnetic field. We report on the robustness in the length of the quantized plateaus and improvements in the quantization as a result of the applied B field.