Engineering Future Quantum Technologies in Low-Dimensional Systems

Classically electrons in a three-dimensional solid can change their momentum in all possible directions. However, electrons in semiconductors can be manipulated so that they are constrained to move in lower dimensions. One of the perfect examples of such a system is a semiconductor heterostructure of GaAs/AlGaAs forming a plane of electrons, only a few nanometer thick, at its junction where electrons possessing quantised energy and freedom to change momentum in the plane. Such remarkable ensemble of non-interacting electrons is known as the two-dimensional electron gas (2DEG). The electrons in a 2DEG system are highly mobile and at low temperatures their motion is mainly scattering free due to the reduction in the interaction with lattice vibrations (phonons) and there is little impurity scattering. When the 2D electrons are electrostatically squeezed to form a narrow, 1D channel whose effective size is less than the electron mean free path for scattering then quantum phenomena associated with the electrons becomes resolved. In this situation, the energy of 1D electrons becomes quantised and discrete levels are formed. At a low carrier concentration of electrons, if the potential which is confining the 1D electrons is relaxed then electrons can arrange themselves into a periodic zig- zag manner forming a Wigner Crystal, named after Wigner who first predicted such a phenomenon in metal in 1936. Recently the distortion of a line of electrons into a zig-zag and then into two separate rows of electrons was observed and associated rich spin and charge phases. A very subtle change in confinement can result in two rows emerging from a zig-zag state which indicates that there is a narrow range where wavefunctions separate and form entangled states. Entanglement is a remarkable phenomenon in which a change in state of one electron will introduce a change in state of another. This amazing property forms the basis for quantum information processing with practical consequences related to quantum technologies, which will be investigated in this proposal.

Another most important aspect of my Fellowship proposal is investigating the zig-zag regime or relaxed 1D system in search of fractional quantum states in the absence of a magnetic field. In the presence of a large magnetic field the energy of a 2DEG is quantized to form Landau levels which gave rise to two celebrated discoveries of the Integer and fractional quantum Hall effects in 1980 and 1982 respectively. Such unexpected revelations then pose a question whether fractional quantised states in the absence of any magnetic field in any lattice or topological insulators could ever be observed? However, there were no reports of observations of any fractional states without a magnetic field until the recent discovery of fractional charges of e/2 and e/4 arising from the relaxed zig-zag state in a Germanium-based 1D system. The proposal is inspired by this and the recent experimental finding of non-magnetic self-organised fractional quantum states in tradition GaAs based 1D quantum wires, which was completely unanticipated.

The research aim is to introduce new insights, and new aspects of quantum physics, by exploiting the interaction effects in low-dimensional semiconductors by manipulating electron wavefunctions in a controllable manner to allow technological exploitation of basic quantum physics. The major challenges to be investigated: spin and charge manipulation, demonstrating electron entanglement and detection, mapping self-organised fractional states and their spin states, controlled manipulation and detection of hybrid fractional states and establishing if they are entangled. This research proposal opens up a new area in the quantum physics of condensed matter with the generation of Non-Abelian fractions which can be used in a Topological Quantum Computation scheme.

I envisage the research work outlined in this proposal will arouse immense interest in all sectors including non-specialists due to its very fundamental nature. The research work proposed in this Fellowship programme will have direct impact on various disciplines such as 1) academic communities, general public interested in fundamental aspects of quantum physics with applications in quantum technologies and material scientists, 2) industries interested in the hardware and software of quantum information technology and c) industrial organisations involved in the manufacturing of high magnetic field cryogenic equipment and precision measurement units. An important pathway to impact is the acceptability of new techniques and methods by a wider scientific community. The first step in this regard will be publishing results in impactful physics and interdisciplinary journals on an open-access basis and presenting work at domestic and international conferences for extending collaboration and networking. The results showing how the integration of interactions creates new rules of electron transport leading to fractional quantum states in nanostructures will be investigated with inputs from theoretical and experimental partners which will advance further theoretical and experimental work globally. These results will be of interest to many material scientists and engineers for growing quantum materials of the highest quality which will have significant scientific and commercial impact.

The successful developments in the project will have profound implications for quantum cryptography, large databases, quantum logic, quantum sensors and quantum metrology. In this research activity, the entanglement of electrons in highly interacting systems will be sought, this may have important implications for quantum logic operations either solely or integrated with quantum communications for a totally quantum organisation. The National Physical Laboratory, a world leader in quantum metrology are interested in the fundamental physics of high accuracy measurements of the electron charge including fractional states which will emerge from this work. This will have a strong impact on the discovery and robustness of the finding. Toshiba Cambridge Research Laboratory are an enthusiastic partner in this research programme, and their expertise in quantum communications will be utilised in creating new prototypes for quantum technologies.

There is a considerable amount of information published on the beneficial economic and social effects, such as quality of life, of the development of quantum information such as rapid search of large databases of benefit in drug discovery, security, healthcare, etc. The development of a better scheme of quantum information based on the work here will generate considerable momentum in this regard and stimulate development of quantum information schemes. I have collaborations with existing companies and in the event of patentable results will discuss licensing with UCL Business as well as the possible formation of start-ups. Success in these endeavours will benefit the economy of the UK, more rapid availability of data and enhanced security will be of importance in policymaking. Institutions and companies which are not present collaborators will be sought to broaden our appeal and create a further parallel pathway.

Awareness of research on Quantum Technologies will be promoted using a dedicated website and social media channels. I will organise summer visits of school students for a day with lectures and demonstration on the fundamentals of quantum physics and technology. In collaboration with the IOP, public lecturers and Webinars on the subject will be organised, and for academic outreach, based on previous year's success of organising an international conference based on "Advances in Quantum Transport..." I will continue organising its future series in collaboration with the IOP and other industry partners.