Spin orbit coupling at the level of a single electron

We utilize electron counting techniques to distinguish a spin conserving fast tunneling process and a slower process involving spin flips in AlGaAs/GaAs-based double quantum dots. By studying the dependence of the rates on the interdot tunnel coupling of the two dots, we find that as many as 4% of the tunneling events occur with a spin flip related to spin-orbit coupling in GaAs. Our measurement has a fidelity of 99 % in terms of resolving whether a tunneling event occurred with a spin flip or not

Single-electron current sources: towards a refined definition of ampere

Controlling electrons at the level of elementary charge $e$ has been demonstrated experimentally already in the 1980's. Ever since, producing an electrical current $ef$, or its integer multiple, at a drive frequency $f$ has been in a focus of research for metrological purposes. In this review we first discuss the generic physical phenomena and technical constraints that influence charge transport. We then present the broad variety of proposed realizations. Some of them have already proven experimentally to nearly fulfill the demanding needs, in terms of transfer errors and transfer rate, of quantum metrology of electrical quantities, whereas some others are currently "just" wild ideas, still often potentially competitive if technical constraints can be lifted. We also discuss the important issues of read-out of single-electron events and potential error correction schemes based on them. Finally, we give an account of the status of single-electron current sources in the bigger framework of electric quantum standards and of the future international SI system of units, and briefly discuss the applications and uses of single-electron devices outside the metrological context.Comment: 55 pages, 38 figures; (v2) fixed typos and misformatted references, reworded the section on AC pump

Environmentally activated tunneling events in a hybrid single-electron box

We have measured individual tunneling events and Coulomb step shapes in single-electron boxes with opaque superconductor–normal metal tunnel junctions. We observe anomalous broadening of the Coulomb step with decreasing temperature in a manner that is consistent with activation of first-order tunneling events by an external dissipative electromagnetic environment. We demonstrate that the rates for energetically unfavorable tunneling events saturate to finite values at low temperatures, and that the saturation level can be suppressed by more than an order of magnitude by a capacitive shunt near the device. The findings are important in assessing the performance limits of any single-electronic device. In particular, master-equation-based simulations show that the electromagnetic environment realized in the capacitively shunted devices allows for a metrologically accurate charge pump based on hybrid tunnel junctions.Peer reviewe

Extreme reductions of entropy in an electronic double dot

We experimentally study negative fluctuations of stochastic entropy production in an electronic double dot operating in nonequilibrium steady-state conditions. We record millions of random electron tunneling events at different bias points, thus collecting extensive statistics. We show that for all bias voltages the experimental average values of the minima of stochastic entropy production lie above $-k_B$, where $k_B$ is the Boltzmann constant, in agreement with recent theoretical predictions for nonequilibrium steady states. Furthermore, we also demonstrate that the experimental cumulative distribution of the entropy production minima is bounded, at all times and for all bias voltages, by a universal expression predicted by the theory. We also extend our theory by deriving a general bound for the average value of the maximum heat absorbed by a mesoscopic system from the environment and compare this result with experimental data. Finally, we show by numerical simulations that these results are not necessarily valid under non-stationary conditions.Comment: 16 pages, 12 figure

Photon assisted tunneling as an origin of the Dynes density of states

We show that the effect of a high-temperature environment in current transport through a normal metal-insulator-superconductor tunnel junction can be described by an effective density of states (DOS) in the superconductor. In the limit of a resistive low-ohmic environment, this DOS reduces into the well-known Dynes form. Our theoretical result is supported by experiments in engineered environments. We apply our findings to improve the performance of a single-electron turnstile, a potential candidate for a metrological current source.Comment: 4+3 pages, 4 figures; updated to the published version, includes EPAPS supplementary materia

Artturi Assists Finnish Advisers and Farmers to Succeed in Grass-Based Dairy Production

Artturi is a collective name for a wide range of services. It is a common tool for different bodies who share an interest in strengthening grass-based dairy production in Finland: research, advisory service and industries. The Service is named after A. I. (Artturi Ilmari) Virtanen, the Finnish scientist who was awarded the Nobel prize in 1945, partly based on his work in developing the ensiling process of grass. The Artturi web site is available in Internet at: http://www.agronet.fi/artturi. Access to Artturi Services is free and no registration is required. The language used is Finnish. During summer 2003, 15,000 visits were recorded at the web site

Characterization of aluminum oxide tunnel barriers by combining transport measurements and transmission electron microscopy imaging

We present two approaches for studying the uniformity of a tunnel barrier. The first approach is based on measuring single-electron and two-electron tunneling in a hybrid single-electron transistor. Our measurements indicate that the effective area of a conduction channel is about one order of magnitude larger than predicted by theoretical calculations. With the second method, transmission electron microscopy, we demonstrate that variations in the barrier thickness are a plausible explanation for the larger effective area and an enhancement of higher order tunneling processes.Peer reviewe

Parallel pumping of electrons

We present simultaneous operation of ten single-electron turnstiles leading to one order of magnitude increase in current level up to 100 pA. Our analysis of device uniformity and background charge stability implies that the parallelization can be made without compromising the strict requirements of accuracy and current level set by quantum metrology. In addition, we discuss how offset charge instability limits the integration scale of single-electron turnstiles.Comment: 6 pages, 4 figures, 1 tabl