Coulomb collisions of hot and cold single electrons in series-coupled silicon single-electron pumps

Precise understanding of the Coulomb interaction between single electrons is vital to achieve accurate single-electron control toward quantum current standards and quantum information processing. Since the strength of the Coulomb interaction increases with decreasing distance, a collision experiment of single electrons would be an ideal way to investigate it. It would be useful to study such a Coulomb collision in silicon single-electron pumps, which can accurately transfer single electrons one by one, while silicon systems have not been used for making Coulomb collisions at the single-electron level. Here, we made two series-coupled tunable-barrier single-electron pumps in silicon and used one to inject a hot single electron into the other pump in each pumping cycle. The hot single electron collides with a cold single electron confined in the other single-electron pump. We observed a current flow due to ejection not only of the hot single electron but also of the confined cold single electron. The latter leads to an excess current at a current plateau at a certain voltage range. We also found that increasing the number of cold electrons from one to two increased the cold-electron current by at least twofold. These results can be explained by a charging effect due to the Coulomb interaction. This observation is valuable to understand single-electron dynamics in the silicon single-electron devices toward accurate current generation and quantum manipulation of flying single electrons

Bottom-up fabrication of Si nanodot transistors using the nc-Si dots solution

A new approach to fabricate nanometer-scale silicon devices is recently attracting much attention, which combines the conventional top-down silicon processing techniques and the bottom-up assembly of silicon nanodots, whose structures are controlled on the atomic scale. This technique enables to investigate the electronic states and transport properties of strongly-coupled multiple nanodots which will be crucial particularly for quantum information device applications. Various unique properties have been studied in such systems. For example, electrostatic interactions have been investigated for double Si dots [1] and for the two-dimensional Si multidots [2]. Coherent wavefunction coupling and associated quasi-molecular states have also been observed for a tunnel-coupled double Si nanodots [3]. In addition, metal-insulator transition has been investigated for an artificial lattice of self-organized nano-paraticles [4]. In this paper we propose and examine a novel technique of fabricating nanoscale transistors with a Si nanodot cluster as a channel based on the self-assembly of the nanocrystalline Si dots from the solution on the patterned SOI substrates

Giga-Hertz quantized charge pumping in bottom gate defined InAs nanowire quantum dots

Semiconducting nanowires (NWs) are a versatile, highly tunable material platform at the heart of many new developments in nanoscale and quantum physics. Here, we demonstrate charge pumping, i.e., the controlled transport of individual electrons through an InAs NW quantum dot (QD) device at frequencies up to $1.3\,$GHz. The QD is induced electrostatically in the NW by a series of local bottom gates in a state of the art device geometry. A periodic modulation of a single gate is enough to obtain a dc current proportional to the frequency of the modulation. The dc bias, the modulation amplitude and the gate voltages on the local gates can be used to control the number of charges conveyed per cycle. Charge pumping in InAs NWs is relevant not only in metrology as a current standard, but also opens up the opportunity to investigate a variety of exotic states of matter, e.g. Majorana modes, by single electron spectroscopy and correlation experiments.Comment: 21 page

Dispersively detected Pauli Spin-Blockade in a Silicon Nanowire Field-Effect Transistor

We report the dispersive readout of the spin state of a double quantum dot formed at the corner states of a silicon nanowire field-effect transistor. Two face-to-face top-gate electrodes allow us to independently tune the charge occupation of the quantum dot system down to the few-electron limit. We measure the charge stability of the double quantum dot in DC transport as well as dispersively via in-situ gate-based radio frequency reflectometry, where one top-gate electrode is connected to a resonator. The latter removes the need for external charge sensors in quantum computing architectures and provides a compact way to readout the dispersive shift caused by changes in the quantum capacitance during interdot charge transitions. Here, we observe Pauli spin-blockade in the high-frequency response of the circuit at finite magnetic fields between singlet and triplet states. The blockade is lifted at higher magnetic fields when intra-dot triplet states become the ground state configuration. A lineshape analysis of the dispersive phase shift reveals furthermore an intradot valley-orbit splitting $\Delta_{vo}$ of 145 $\mu$eV. Our results open up the possibility to operate compact CMOS technology as a singlet-triplet qubit and make split-gate silicon nanowire architectures an ideal candidate for the study of spin dynamics