The student will explore the quantum nature of devices fabricated with nanoscale dimensions. This research will impact on future integrated circuit technology as devices continue to shrink and will also lead to advances in more exotic device architectures such as quantum computers. The underlying physics to be studied and exploited is that of spin-1/2 particles (fermions) interacting with a user-defined periodic potential. In our case the periodic potential is defined by the location of deterministically placed dopant atoms in the host germanium lattice, and the spins are the valence electrons of these dopants. These experiments will address many-body quantum physicstopics that have been puzzling scientists for decades, such as those of the metalinsulator transition (Mott-Hubbard physics), and will lead to the development of quantum simulators, which are a fast route to performing quantum computation. The project is practical in nature and the UCL component involves the development of fabrication processes to make few and single dopant atom devices. The student will use the tip of a scanning tunnelling microscope (STM) to pattern a single atomic layer of hydrogen, providing a masking layer to incorporate the dopants into the germanium surface. In addition to learning the highly sophisticated technique of STM, the student will develop a detailed understanding of the unique chemistry of the arsine/germanium interface and develop the process of creating smooth, wellordered germanium overlayers using molecular beam epitaxy. Finally they will make contacts to these devices using cleanroom processing technology, including the techniques of electron beam lithography (EBL), reactive ion etching (RIE) and metal evaporation.
The student will also spend time at the Paul Scherrer Institute (PSI) near Zurich, where the devices will be studied using magnetotransport electrical measurements and THz spectroscopy experiments at cryogenic temperatures. The measurements are in the spectral and time domain, and will demonstrate the coherent control of donors in germanium in the far infrared. As a host for dopant atom devices, germanium is expected to have many benefits over silicon for quantum technologies, including spin based quantum computers, and the aim of these measurements is to reveal these benefits. Benefits include stronger-spin orbit coupling, vastly improved spin-photon interfacing, and insensitivity to the valley interference that decoheres quantum bits. Additionally, the student will be involved in experiments to determine other device characteristics using other synchrotron based techniques such as angle-resolved photoemission spectroscopy (ARPES), X-ray photoelectron diffraction (XPD) and photoemission electron spectroscopy (PEEM).