We report on an experimental investigation of the direct current induced by transmitting a surface acoustic wave (SAW) with frequency 2.7 GHz through a quasi-one-dimensional (1D) channel defined in a GaAs - AlGaAs heterostructure by a split gate, when the SAW wavelength was approximately equal to the channel length. At low SAW power levels the current reveals oscillatory behaviour as a function of the gate voltage with maxima between the plateaux of quantized 1D conductance. At high SAW power levels, an acoustoelectric current was observed at gate voltages beyond pinch-off. In this region the current displays a step-like behaviour as a function of the gate voltage (or of the SAW power) with the magnitude corresponding to the transfer of one electron per SAW cycle. We interpret this as due to trapping of electrons in the moving SAW-induced potential minima with the number of electrons in each minimum being controlled by the electron - electron interactions. As the number of electrons is reduced, the classical Coulomb charging energy becomes the Mott - Hubbard gap between two electrons and finally the system becomes a sliding Mott insulator with one electron in each well.

We report a detailed experimental study of the quantized acoustoelectric current induced by a surface acoustic wave in a one-dimensional channel defined in a GaAs-Al x Ga 1Ϫx As heterostructure by a split gate. The current measured as a function of the gate voltage demonstrates quantized plateaus in units of Iϭe f where e is the electron charge and f is the surface acoustic wave frequency, the effect first observed by Shilton et al. The quantization is due to trapping of electrons in the moving potential wells induced by the surface acoustic wave, with the number of electrons in each well controlled by electron-electron repulsion. The experimental results demonstrate that acoustic charge transport in a one-dimensional channel may be a viable means of producing a standard of electrical current.

We describe in detail a set of ideas for implementing qubits, quantum gates and quantum gate networks in a semiconductor heterostructure device. Our proposal is based on an extension of the technology used for surface acoustic wave (SAW) based single-electron transport devices. These devices allow single electrons to be captured from a two-dimensional electron gas in the potential minima of a SAW. We discuss how this technology can be adapted to allow the capture of electrons in pure spin states and how both single and two-qubit gates can be constructed using magnetic and non-magnetic gate technology. We give designs for readout gates to allow the spin state of the electrons to be measured and discuss how combinations of gates can be connected to make multi-qubit networks. Finally we consider decoherence and other sources of error, and how they can be minimized for our design

We report the first observation of the direct current induced by a surface acoustic wave through a quantum point contact defined in a GaAs-AlGaAs two-dimensional electron gas by means of a split gate. We have observed giant oscillations in the acoustoelectric current as a function of gate voltage, with minima corresponding to the plateaux in quantum point contact conductivity. A theoretical consideration is presented which explains the observed peaks in terms of the matching of sound velocity with electron velocity in the upper one-dimensional subband of the quantum point contact.The interaction of a surface acoustic wave (SAW) with a two-dimensional electron gas (2DEG) in a GaAs-Al x Ga 1−x As heterostructure has recently attracted much attention [1][2][3][4][5][6][7][8][9][10]. Usually, two kinds of effect are studied. The first kind is the attenuation and change in velocity of the sound wave due to interaction with electrons. For small amplitudes, these effects are linear in the acoustic wave amplitude. Analysis of these effects allows us, in principle, to study the linear response of carriers to alternating strain deformation and electric fields at the SAW frequency. An important consideration is that these measurements do not require any contacts to be made to the sample. Very interesting studies of these effects in quantum Hall systems were carried out, in particular, in [1,4].The second class of studies deal with the so-called acoustoelectric effects in 2DEGs. These are due to a drag of the 2D electrons by the SAW [5-10], and for small signals are quadratic in the SAW amplitude. As described, an acoustic wave, while travelling across the sample is attenuated due to interaction with the electrons, and transfers some of its momentum to them. As a result a d.c. current in a closed circuit appears (the acoustoelectric current). In an open circuit, a d.c. voltage is generated. Thus in principle these acoustoelectric effects can be used to study both the d.c. and a.c. response of the carriers.Drag of the electrons in a quantum point contact by non-equilibrium phonons has been considered in [11]. This paper discussed a current flowing through a channel due to a 'phonon wind' in the leads, and predicted its quantization, similar to the conductance quantization. We believe that such a mechanism is not important in our case, because of the strong screening of the interaction outside the QPC.In this letter we present the first experimental and theoretical study of the acoustoelectric current in a quasi-one-dimensional ballistic channel defined in a 2DEG by split-gate-induced depletion. We observed a very specific behaviour of the acoustoelectric current, qualitatively different from the behaviour of the conductance.

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