V. I. Talyanskii

High-frequency single-electron transport in a quasi-one-dimensional GaAs channel induced by surface acoustic waves

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.

High-frequency acousto-electric single-photon source

We propose a single optical photon source for quantum cryptography based on the acousto-electric effect. Surface acoustic waves (SAWs) propagating through a quasi-one-dimensional channel have been shown to produce packets of electrons which reside in the SAW minima and travel at the velocity of sound. In our scheme these electron packets are injected into a p-type region, resulting in photon emission. Since the number of electrons in each packet can be controlled down to a single electron, a stream of single (or N) photon states, with a creation time strongly correlated with the driving acoustic field, should be generated.

On the acoustoelectric current in a one-dimensional channel

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.

Experimental study of the acoustoelectric effects in GaAs-AlGaAs heterostructures

We present the results of a detailed experimental study of the electric current and voltage induced in the 2DEG of a GaAs-AlGaAs heterostructure by a surface acoustic wave (SAW). New results are obtained for these acoustoelectric effects at zero and low (<0.1 T) magnetic fields. At zero magnetic field the acoustoelectric current (voltage) was found to show a non-monotonic temperature dependence with a maximum at 40-50 K. Measurements on high-mobility 2DEGs where the electron mean free path is comparable with the SAW wavelength reveal geometric resonances of the cyclotron orbit with the SAW wavelength. With increasing magnetic field the acoustoelectric effects increase significantly and display rich oscillatory structure. We compare our data for the high-magnetic-field regime with that published in the literature.

An acoustoelectric single photon detector

We propose a novel single photon detector for quantum information processing and for general applications in areas where the detection of ultra weak photon fluxes is required. The detector is also capable of discriminating between different numbers of photons in a light pulse. It uses acoustic charge transport in order to transfer photogenerated electrons and holes to areas where their charge can be detected by single electron transistors. Preliminary experimental results on the fidelity of the acoustic charge transport are presented, which allows us to make estimates of the detectors performance.

Charge pumping and current quantization in surface acoustic-wave-driven carbon nanotube devices

We investigate charge pumping in semiconducting carbon nanotubes by a travelling potential wave on the surface of a piezoelectric quartz substrate. We estimate the magnitude and profile of the potential wave as its passes the nanotubes and show how this results in the pumping of charge in packets. By tuning the potential of a side gate, transport of either electron or hole packets can be realized, reversing the direction of the current. We furthermore discuss a specific device in which the current shows a distinct plateau as a function of gate voltage, wave amplitude and frequency. Interestingly, the current plateau appears at a value of ef, where e is the electron charge and f the frequency of the potential wave. We discuss possible mechanisms that would lead to current quantization in our devices.

Acoustoelectric current in submicron-separated quantum wires

We measure acoustoelectric current in two submicron-separated quasi-one-dimensional wires formed in an AlGaAs∕GaAs heterostructure. We show that independent control of acoustoelectric current in both wires can be achieved with a suitably chosen geometry of Schottky gates. The implications of the results on two proposed uses of single-electron acoustoelectric current flow are discussed: a single-photon source and an acoustoelectrically driven quantum computer.

Fidelity of the charge transport by surface acoustic waves in a GaAs quantum well

Charge transport in one- and two-dimensional GaAs-based electronic systems by surface acoustic waves (SAWs) is expected to find application in quantum information processing and metrology. In the charge transport by a SAW (referred to as the acoustic charge transport (ACT)), electrons are transported in packets residing in the SAW potential minima along channels formed in a GaAs quantum well or heterojunction, which play a role similar to that of wires in standard electronic circuits. The potential of ACT circuits for quantum information processing stems from their ability to precisely control the position and the spin of single electrons. Traps in the ACT channel may capture an electron from one SAW minimum and release it later into another, thereby reducing the fidelity of the ACT transport and compromising device performance. In this paper, we describe a novel experimental technique for the characterization of the ACT fidelity using an acoustoelectric Y-branch switch. The results are used to assess the performance of an acoustoelectric discriminating photon detector for quantum information processing.

High-frequency single-electron transport and the quantized acoustoelectric effect

Abstract A quantized current may be induced through a one-dimensional channel by a strong surface acoustic wave. Such devices offer a possible route towards a current standard, with the high induced current being suitable for metrological applications. We report on new observations of quantized charge transport in etched constrictions. Plateaux flat to a precision of around ±50 parts per million are compared to results obtained in Schottky gated samples. The influence of a perpendicular magnetic field on the quantization is discussed for the first time.

Low-frequency edge excitations in an electrostatically confined GaAs-AlGaAs two-dimensional electron gas

We report an experimental study of the propagation of low-frequency (1-30 MHz) edge excitations in a two-dimensional electron gas confined electrostatically by means of gate induced depletion. This technique allows control of edge channel structure without change of the bulk properties of the electron gas. We have observed a strong dependence of the velocity of the edge excitations on gate voltage and demonstrate that such spectroscopy is a sensitive probe of the two-dimensional edge electronic structure.