Single-electron pumping in silicon quantum dots

The present definition of the ampere in the International System of Units is based on Ampere's law. This classical definition requires a large and impractical set-up that is vulnerable to uncertainties of other units such as mass. There has been great global interest in redefining the ampere such that it would be based on a fixed value for the elementary charge. This quantum standard can potentially be realized by single-electron current sources that output a fixed integer number of electrons at a precise frequency. To date, single-charge pumps based on semiconductor quantum dots have exhibited the lowest uncertainties at relatively high currents. In this thesis, we study a silicon quantum dot that is driven with radio frequency waveforms to implement quantized single-electron pumping. We find that our pump has potential in current metrology in terms of the accuracy and yield. In this mainly experimental thesis, we discuss also the pump architecture, fabrication techniques, and experimental methods. We study the electrical confinement of the pump dot and confirm that it can be used to increase the charging energy and the energy of the first excited state. We utilize this confinement to increase the pumping accuracy. Furthermore, we demonstrate an electron counting scheme in our device architecture and show that it is consistent with the direct output current of the pump. We also introduce full three-waveform radio frequency control and utilize it to demonstrate bidirectional pumping with convenient reversal of the output current. Previously, this has been challenging in semiconductor pumps due to the asymmetries in the devices and operation protocols. In addition, we study non-equilibrium fluctuation relations in a hybrid superconductor-normal-metal single-electron box. We confirm that the Jarzynski equality and the Crooks fluctuation theorem both are followed by the studied system. These are the first experimental studies of the fluctuation relations in single-electron devices. The device architecture and methods presented in this thesis provide an important contribution towards the quantum ampere. We conclude that silicon quantum dots have great potential in realizing the emerging quantum ampere.