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

Control of the Coulomb interaction between single electrons is vital for realizing quantum information processing using flying electrons and, particularly, for the realization of deterministic two-qubit operations. 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. Moreover, it would be useful to study such a Coulomb collision in silicon system, which has been extensively studied for qubit applications but so far has 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 an important step toward quantum manipulation of flying single electrons in silicon

Picosecond coherent electron motion in a silicon single-electron source

Understanding ultrafast coherent electron dynamics is necessary for application of a single-electron source to metrological standards, quantum information processing, including electron quantum optics, and quantum sensing. While the dynamics of an electron emitted from the source has been extensively studied, there is as yet no study of the dynamics inside the source. This is because the speed of the internal dynamics is typically higher than 100 GHz, beyond state-of-the-art experimental bandwidth. Here, we theoretically and experimentally demonstrate that the internal dynamics in a silicon singleelectron source comprising a dynamic quantum dot can be detected, utilising a resonant level with which the dynamics is read out as gate-dependent current oscillations. Our experimental observation and simulation with realistic parameters show that an electron wave packet spatially oscillates quantum-coherently at $\sim$ 200 GHz inside the source. Our results will lead to a protocol for detecting such fast dynamics in a cavity and offer a means of engineering electron wave packets. This could allow high-accuracy current sources, high-resolution and high-speed electromagnetic-field sensing, and high-fidelity initialisation of flying qubits

Evidence for universality of tunable-barrier electron pumps

We review recent precision measurements on semiconductor tunable-barrier electron pumps operating in a ratchet mode. Seven studies on five different designs of pumps have reported measurements of the pump current with relative total uncertainties around 10-6 or less. Combined with theoretical models of electron capture by the pumps, these experimental data exhibits encouraging evidence that the pumps operate according to a universal mechanism, independent of the details of device design. Evidence for robustness of the pump current against changes in the control parameters is at a more preliminary stage, but also encouraging, with two studies reporting robustness of the pump current against three or more parameters in the range of ∼5 × 10-7 to ∼2 × 10-6. This review highlights the need for an agreed protocol for tuning the electron pump for optimal operation, as well as more rigorous evaluations of the robustness in a wide range of pump designs

Realisation of a quantum current standard at liquid helium temperature with sub-ppm reproducibility

Mate Jenein mukaan kyseessä on post-print. Kysytty erikseen.A silicon electron pump operating at the temperature of liquid helium has demonstrated repeatable operation with sub-ppm accuracy. The pump current, approximately 168 pA, is measured by three laboratories, and the measurements agree with the expected current ef within the uncertainties which range from 0.2 ppm to 1.3 ppm. All the measurements are carried out in zero applied magnetic field, and the pump drive signal is a sine wave. The combination of simple operating conditions with high accuracy demonstrates the possibility that an electron pump can operate as a current standard in a National Measurement Institute. We also discuss other practical aspects of using the electron pump as a current standard, such as testing its robustness to changes in the control parameters, and using a rapid tuning procedure to locate the optimal operation point.Peer reviewe