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.

State readout is a key requirement for a quantum computer. For semiconductor-based qubit devices it is usually accomplished using a separate mesoscopic electrometer. Here we demonstrate a simple detection scheme in which a radio-frequency resonant circuit coupled to a semiconductor double quantum dot is used to probe its charge and spin states. These results demonstrate a new non-invasive technique for measuring charge and spin states in quantum dot systems without requiring a separate mesoscopic detector. PACS numbers:State readout is a key requirement for a quantum information processor. For semiconductor-based qubit devices this is usually accomplished using a separate mesoscopic electrometer such as a quantum point contact (QPC) [1]. Non-invasive detection using a QPC has been critical to recent advances in coherent control of few-electron double quantum dots [2], allowing their charge configurations to be mapped in regimes where transport through the double dot itself is not measurable [3]. Furthermore, through spin-to-charge conversion techniques, spin state measurements of single and double dots have been demonstrated using QPCs [4,5].Resonant microwave circuits have played an important role in performing sensitive measurements of mesoscopic devices. In the case of superconducting charge qubits, earlier schemes used a proximal single electron transistor (SET) charge detector to perform state readout [6,7]. This SET was coupled to an impedance matching rf resonant circuit to form an rf-SET which had dramatically improved sensitivity and bandwidth [8]. Similarly, an rf-QPC has also been realised for broadband charge detection of semiconductor quantum dot devices [9,10].More recently, state readout of a superconducting charge qubit has been accomplished by directly coupling it to a microwave resonant circuit [11][12][13]. Working in the dispersive regime where the resonator and qubit bandgap energies are detuned, the qubit has a state-dependent 'quantum capacitance' which causes a shift in the resonator frequency [14]. This frequency shift can then be detected using standard homodyne detection techniques.In this Letter, we demonstrate dispersive detection using a resonant circuit coupled directly to an AlGaAs/GaAs few-electron double quantum dot device. This allows us to probe the charge state of a single electron confined to a double quantum dot. We also perform a spin-state measurement for a pair of electrons using the resonant circuit. These results demonstrate a new and non-invasive technique for measuring charge and spin states in semiconductor quantum dot systems without the need for a separate mesoscopic detector.In using the resonator to probe the state of a double quantum dot we consider the double dot as a charge qubit where a single electron occupies either the ground state of one dot or the other [16]. The Hamiltonian for this two level system is given by H = 1 2 σ z + tσ x , where is the detuning between the two dot chemical potential energies and t is the interdot tunnel coupling energy which m...

Measurements are presented of a device designed to cool a 6 microm;{2} region of 2D electron gas using quantum dots. Electrostatic effects are found to be significant in the device, and a model that accounts for them is developed. At ambient electron temperatures above 120 mK the results are consistent with the model and the base temperature of the cooled region is estimated. At an ambient electron temperature of 280 mK, the 6 microm;{2} region is found to be cooled below 190 mK. Below 120 mK the results deviate from predictions, which is attributed to reduced electron-electron scattering rates.

Egg albumen as the dielectric, and dissolvable Mg and W as the top and bottom electrodes are used to fabricate water-soluble memristors. 4 × 4 cross-bar configuration memristor devices show a bipolar resistive switching behavior with a high to low resistance ratio in the range of 1 × 10(2) to 1 × 10(4), higher than most other biomaterial-based memristors, and a retention time over 10(4) s without any sign of deterioration, demonstrating its high stability and reliability. Metal filaments accompanied by hopping conduction are believed to be responsible for the switching behavior of the memory devices. The Mg and W electrodes, and albumen film all can be dissolved in water within 72 h, showing their transient characteristics. This work demonstrates a new way to fabricate biocompatible and dissolvable electronic devices by using cheap, abundant, and 100% natural materials for the forthcoming bioelectronics era as well as for environmental sensors when the Internet of things takes off.

We present scanning-probe images and magnetic-field plots which reveal fractal conductance fluctuations in a quantum billiard. The quantum billiard is drawn and tuned using erasable electrostatic lithography, where the scanning probe draws patterns of surface charge in the same environment used for measurements. A periodicity in magnetic field, which is observed in both the images and plots, suggests the presence of classical orbits. Subsequent high-pass filtered highresolution images resemble the predicted probability density of scarred wave functions, which describe the classical orbits. , are observed in disordered systems due to multiple-path interference as electrons scatter from random impurities [1]. A quantum billiard is a large quantum dot where electron trajectories are ballistic, meaning scattering occurs predominantly at the billiard boundary. If the electron phase coherence length is longer than the billiard dimensions, then conductance fluctuations can also be observed in quantum billiards where electrons scatter off the billiard boundary instead of impurities [2][3][4][5]. A soft-walled quantum billiard is a classically mixed system, with regions of regular and chaotic behavior, characterized by the presence of fractal magnetoconductance fluctuations [4,6,7]. The system is chaotic in the sense that a small change, in the magnetic field for example, strongly modifies conductance on an arbitrarily fine scale. Quantum billiards often exhibit Aharonov-Bohm like [1] periodic conductance fluctuations, which are understood to be the signature of stable closed-loop orbits with well defined areas whose quantum states are preferentially excited due to collimation from the leads [2]. The amplitude of the associated wave functions, which are known as scarred wave functions, are concentrated along the underlying classical trajectories and are found through simulation to also exist periodically in magnetic field [8][9][10]. In this letter we provide a further link between experiment and simulation by presenting high resolution scanning probe images of fractal conductance fluctuations which reveal structure remarkably similar to that seen in theoretical images of scarred wave functions [8]. Figure 1 illustrates the billiard construction. A 2D electron system (2DES) with electron mobility 6 10 5 × cm 2 V -1 s -1 and density 11 10 1 . 3 × cm -2 forms at a GaAs/AlGaAs heterojunction 97 nm beneath the surface. The billiard is defined from the 2DES using erasable electrostatic lithography (EEL) where a conductive scanning probe draws spots of negative charge on the GaAs surface to locally deplete 2DES electrons [11]. Uniquely, EEL uses the same low-temperature high-vacuum environment as used for measurement, so device geometry can be modified during the experiment. A row of EEL spots, separated by 100 nm, creates a linear barrier in the 2DES which defines the quantum billiard walls. The lithographic dimension of the billiard is 2 by 3.5 m, but EEL line width and lateral depletion decrease the 2DES billiard dimension ...