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...

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We report on high-accuracy measurements of quantized current, sourced by a tunable-barrier single-electron pump at frequencies f up to 1 GHz. The measurements were performed with a new picoammeter instrument, traceable to the Josephson and quantum Hall effects. Current quantization according to I = ef with e the elementary charge was confirmed at f = 545 MHz with a total relative uncertainty of 0.2 ppm, improving the state of the art by about a factor of 5. For the first time, the accuracy of a possible future quantum current standard based on single-electron transport was experimentally validated to be better than the best realization of the ampere within the present SI.

We study single-parameter quantized charge pumping via a semiconductor quantum dot in high magnetic fields. The quantum dot is defined between two top gates in an AlGaAs/GaAs heterostructure. Application of an oscillating voltage to one of the gates leads to pumped current plateaus in the gate characteristic, corresponding to controlled transfer of integer multiples of electrons per cycle. In a perpendicular-to-plane magnetic field the plateaus become more pronounced indicating an improved current quantization. Current quantization is sustained up to magnetic fields where full spin polarization of the device can be expected. PACS numbers:Generating well defined currents by manipulating single charges has attracted considerable interest in the last two decades from both fundamental and applied points of view [1]. A particular potential of application lies in the field of metrology to provide a link between time and current units [2]. Different approaches have been studied, such as arrays of tunnel-connected metallic islands controlled by a number of phase shifted ac signals [3,4,5,6] or semiconducting channels along which the potential can be modulated continuously [7,8,9,10,11]. The pumping mechanism demonstrated in Ref.[10] allows gigahertz pumping comparable to surface-acoustic-wave pumps [8] while promising a higher degree of control. It employs three electrodes of which two are modulated at a fixed phase shift and with different amplitudes. In Ref. [11] it was shown that a single modulated voltage signal is sufficient to operate the pump and a numerical investigation indicated the importance of the tunnel barrier shape for improving the accuracy. A possible way to manipulate these tunnel couplings might be the application of a magnetic field owing to its influence on the wave function and the corresponding rearrangement of electrons between quantum states (see for instance [12]). Therefore the operation of such a single-parameter charge pump has been realized in the presented work when a perpendicular-to-plane magnetic field was applied.Two devices have been investigated which were both realized in an AlGaAs/GaAs heterostructure with a carrier concentration of 2.1 × 10 15 m −2 and a mobility of 97 m 2 /Vs in the dark. A 700 nm wide wire connected to two-dimensional electron gases was created by wetetching the doped AlGaAs layer. This channel is crossed by two 100 nm wide Ti-Au finger gates of 250 nm separation. A schematic is shown in the inset of Fig. 1(a). A quantum dot (QD) with discrete quasibound states between the gates can be created by applying sufficiently large negative voltages V 1 and V 2 to gate 1 and gate 2, * Electronic address: Bernd.Kaestner@ptb.de respectively. An additional radiofrequency (rf) signal is coupled to gate 1. The resulting voltages are thereforeat gate 1 and gate 2, respectively. If the oscillation amplitude is high enough, then the bound state drops below the Fermi level during the first half-cycle of the periodic signal and can be loaded with electrons from source. During th...

This paper investigates a scheme for quantized charge pumping based on single-parameter modulation. The device was realized in an AlGaAs-GaAs gated nanowire. We find a remarkable robustness of the quantized regime against variations in the driving signal, which increases with applied rf power. This feature together with its simple configuration makes this device a potential module for a scalable source of quantized current.Comment: Submitted to Appl. Phys. Let