Howe, HHT; (2016) Amplitude, temperature, and frequency dependence of quantum pumps in semiconductor heterostructures. Doctoral thesis , UCL (University College London).

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Abstract

In the rapidly growing field of integrated quantum devices, two particular areas of interest are the development of an on-chip cryogenic current comparator (CCC) for completing the metrological triangle and the development of integrated de- vices for fast qubit operations. This thesis aims to significantly further our understanding of a quantum pump, a device integral to the CCC and potentially critical for realising fast qubit operations. A quantum pump is a device that transfers a discrete number of electrons between two electrically isolated regions when a potential barrier is cyclically oscillated. Initially, quantum pumps were single electron turnstile devices, which were limited in operational frequency by the Coulomb potential of the turnstile. Modern quantum pumps, utilising a dynamic quantum dot in a 2-dimensional electron gas (2DEG), are not limited by frequency. The fast operation of these modern pumps makes them very promising devices for accurately measuring the electron charge and performing fast qubit operations. In this study, we address the technical challenges of measuring a Al- GaAs/GaAs quantum pump and detail the processing and measurement setup. One of the challenges is rectified current swamping pump current. We develop a model for the rectified current and investigate ways to suppress it. We then show how the accuracy of a quantum pump changes as a function of amplitude, temperature, and frequency, and develop a model towards explaining the changes.

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