Superconducting MoSi nanowires

We have fabricated disordered superconducting nanowires of molybdenium silicide. A molybdenium nanowire is first deposited on top of silicon, and the alloy is formed by rapid thermal annealing. The method allows tuning of the crystal growth to optimise, e.g., the resistivity of the alloy for potential applications in quantum phase slip devices and superconducting nanowire single-photon detectors. The wires have effective diameters from 42 to 79 nm, enabling the observation of crossover from conventional superconductivity to regimes affected by thermal and quantum fluctuations. In the smallest diameter wire and at temperatures well below the superconducting critical temperature, we observe residual resistance and negative magnetoresistance, which can be considered as fingerprints of quantum phase slips

Pumping properties of the hybrid single-electron transistor in dissipative environment

Pumping characteristics were studied of the hybrid normal-metal/superconductor single-electron transistor embedded in a high-ohmic environment. Two 3 micrometer-long microstrip resistors of CrOx with a sum resistance R=80kOhm were placed adjacent to this hybrid device. Substantial improvement of pumping and reduction of the subgap leakage were observed in the low-MHz range. At higher frequencies 0.1-1GHz, a slowdown of tunneling due to the enhanced damping and electron heating negatively affected the pumping, as compared to the reference bare devices.Comment: 3 pages 4 figure

Long hold times in a two-junction electron trap

The hold time $\tau$ of a single-electron trap is shown to increase significantly due to suppression of environmentally assisted tunneling events. Using two rf-tight radiation shields instead of a single one, we demonstrate increase of $\tau$ by a factor exceeding $10^3$, up to about 10 hours, for a trap with only two superconductor (S) -- normal-metal (N) tunnel junctions and an on-chip resistor $R$ (R-SNS structure). In the normal state, the improved shielding made it possible to observe $\tau\sim$ 100 s, which is in reasonable agreement with the quantum-leakage-limited level expected for the two-electron cotunneling process.Comment: 4 pages, 3 figure

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

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

Understanding Teacher Evaluation in Finland: A Professional Development Framework

This study explores the characteristics of the teacher evaluation model in Finland. Highlighting the unique qualities of the Finnish case, we also compare these teacher evaluation practices with the increasingly applied value-added model (VAM) for teacher evaluation across the globe. Our analysis revealed that the Finnish Model prioritises teacher empowerment and professional development by carrying out bottom-up evaluation practices. With a clear focus on teacher empowerment and professional development, this framework substantially differs from accountability measures such as VAM, which emphasize rigid data collection procedures and the use of standardized test scores to hold teachers accountable based on their students’ academic performance. This study also revealed that professional development endeavours of teachers are highlighted as the key elements in Finnish teacher evaluation. Ongoing needs analyses for professional development also form the basis for assessing teachers in Finland

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

Excitation of Single Quasiparticles in a Small Superconducting Al Island Connected to Normal-Metal Leads by Tunnel Junctions

We investigate the dynamics of individual quasiparticle excitations on a small superconducting aluminum island connected to normal metallic leads by tunnel junctions. We find the island to be free of excitations within the measurement resolution. This allows us to show that the residual heating, which typically limits experiments on superconductors, has an ultralow value of less than 0.1 aW. By injecting electrons with a periodic gate voltage, we probe electron-phonon interaction and relaxation down to a single quasiparticle excitation pair, with a measured recombination rate of 16 kHz. Our experiment yields a strong test of BCS theory in aluminum as the results are consistent with it without free parameters.Peer reviewe