In a complex system made up of many smaller units, each element will interact with all of its neighbours, and the system tries to arrange itself so that the most favourable bond is formed with each neighbour. However, sometimes the neighbours have requirements that are mutually incompatible and a compromise must be found. If this is the case we describe the system as being frustrated. Frustration occurs widely in nature and is thought to be critical to our understanding of such questions as how do our brains work? and how do proteins fold? The frustrated biological systems described are so complex and so important that the science of frustration has become a major research area and there is great demand for simpler model systems where the interaction strength can be tuned, the model system size can be varied, defects can be introduced in a controlled manner and individual elements can be manipulated, removed or their individual state recorded. In such an ideal system one could unite theory and experiment and begin to understand the underlying physics within this complexity. Magnetic frustration has proved to be the most successful area for finding model systems. Traditionally these were magnetic crystals prepared by solid-state chemistry. However it has recently been shown that it is possible to use nanotechnology to make arrays of magnetic bars sufficiently small and sufficiently close together that the magnetic interactions between them becomes very significant, and that novel geometries can be designed where the magnetic interactions cannot all be satisfied. This development opens up broad new avenues of research in model frustrated systems. In solid-state chemistry one is limited by nature in the geometrical arrangements that are possible, whereas with nanotechnology any pattern that will tessellate can be fabricated into an array, on any length-scale down to the minimum feature size of the lithography. Here I propose to study such ideal systems that are based on frustrated magnetic nanostructures. Our experience from frustrated magnetic chemical structures tells us that triangles and hexagons are the building blocks that favour magnetic frustration. The initial work was done on arrays of magnetic bars that were isolated from one another, but I plan to focus on electrically continuous lattices, such as the hexagonal honeycomb structure so that electrical current can pass through it. The electrical properties of magnetic materials are sensitive to the magnetic structure and so this gives a direct probe of the frustrated structure and one can study its dynamic response to changes in temperature and magnetic field. Magnetic force microscopy (MFM) and scanning Hall probe imaging will be used to image the magnetic structure during these experiments. These in-situ measurements will allow the change in electrical response to be correlated directly with the change in magnetic structure, and will provide important information of the nature of the coupling between the magnetic and electrical properties of ferromagnetic metals, and the role of topology, which is currently very important for new spin-based electronics or spintronics technology. In addition to improving knowledge of diverse other fields, the magnetic arrays that I will make are exciting in their own right. Their unusual and sensitive response to magnetic fields might be useful in sensors. Furthermore the strong coupling between all the elements, and the fact that the magnetic state of individual elements can be both written (changed by applying a magnetic field) and read, means they could potentially be used for novel types of computation, often described as neural networks because they work more like the brain than like a conventional computer.

Historically quantum fluids, the helium liquids near absolute zero, have provided simple model systems which have played a crucial role in the development of key concepts in condensed matter physics. The understanding of superfluidity and broken gauge symmetry; the development of the standard model of correlated fermions; the first unconventional superfluid/superconductor; the central role of topological excitations in two dimensional physics: all these discoveries and insights arose from the study of helium. The study of quantum fluids has also fuelled developments in techniques for producing and measuring low temperatures, high magnetic fields, and a host of novel measurement techniques and instrumentation. We propose to study a variety of low dimensional helium model systems to address fundamental issues in the understanding of strongly correlated quantum matter. We will study helium-3 (fermion) films and helium-4 (boson) films. These films grow as atomic layers on the atomically flat surface of graphite, and the lattice potential experienced by a helium layer can give rise to a triangular superlattice structure. The density of these layers can be varied essentially continuously to tune between different quantum mechanical ground states. These may include ground states theoretically proposed but yet to be unambiguously realized. We will study the quantum phase transitions between different ground states in some detail. We will study the Mott transition between a 2D helium-3 Fermi liquid and a 2D quantum spin liquid and the properties of the hole-doped spin liquid on a triangular lattice. We will attempt to stabilise a Mott insulator on a square lattice and perform a comparable experiment. In the corresponding helium-4 film we will study the superfluid-insulator transition, and investigate possible 2D supersolid behaviour. We will develop a highly ordered graphite substrate with a view to optimising conditions under which to search for the holy grail of unconventional superfluidity in a helium-3 fluid monolayer. We will investigate quantum criticality in the helium-3 bilayer heavy fermion system recently discovered by us. And we will study helium-3 in nano-channels as a one dimensional fermion system, and a possible realization of a Luttinger liquid. These experiments on fermionic and bosonic cold atoms are performed on uniform low dimensional systems in thermodynamic equilibrium at precisely measured temperatures in the range 200 microKelvin to 4K. The lowest temperatures will be produced by nuclear adiabatic demagnetization cryostats in our laboratory. A range of high precision experimental probes will be employed to study these systems. Sensitive NMR techniques developed in our laboratory, based on the detection of the precessing magnetic signal by SQUIDs (Superconducting Quantum Interference Devices), will be used to measure magnetic susceptibility, magnetization and spin dynamics. We will extend measurements of the heat capacity to the lowest temperatures in order to access system entropy and probe the elementary excitations. The superfluid density, and any dissipative component of the response, will be measured by high quality torsional mechanical resonators. We will collaborate on developing graphene based nano-mechanical resonators with wide-bandwidth SQUID amplifier detection. The project is expected to lead to fundamental insights into some of the most central issues in the physics of strongly correlated matter, and impact on the understanding of more complex materials of potential technological relevance. The project will drive innovation of new instrumentation and measurement techniques at an important scientific frontier; the low temperature frontier. As in any frontier science we may encounter the unexpected.

The aim of this proposal is to develop equipment that can take advantage of the discovery of MASER action at room temperature. The MASER (Microwave Amplified Stimulated Emission of Radiation) was in fact discovered before the LASER (Light Amplified Stimulated Emission of Radiation) but required cryogenic cooling and magnetic fields. The associated infrastructure needed to operate the MASER meant that it was used in very few specialist applications such as deep space exploration. Maser research then produced lasers and around the same time, semiconductor amplifiers were developed, which brought further development to a halt. However, they were developed into very useful devices for timekeeping, radio astronomy and deep space communication (Ruby masers) because of their unparalleled low electronic noise as well as a very narrow linewidth of oscillation. The discovery of masing at room temperature is a step change that allows us to consider new instrumentation that would transform low-noise amplifiers, sensors, and clocks. If we can amplify tiny signals and increase signal to noise then we can use them as very low noise amplifiers - these are found in all manner of electronic equipment. The gamechanger is the noise floor of our maser when measured at room temperature. Our ambition therefore is to extend the astounding sensitivity and low noise of existing masers to room-temperature applications, there are two relevant comparators - existing non-ambient technologies and existing room-temperature technologies. For applications as low-noise amplifiers, a key figure of merit is the so-called "noise temperature" which should be as low as possible and for conventional electronic devices is approximately their thermodynamic temperature. The pentacene maser has an estimated noise temperature of 140 milliKelvin and the diamond maser has an estimated noise temperature of less than 2 Kelvin with theory suggesting the noise temperature could be lowered to around 300 milliKelvin, all at room temperature. Our noise floor is 1-2 orders of magnitude lower than the best semiconductor (high electron mobility transistors) available today. So for example we would get better images in a MRI machine or clearer communications. Already we can foresee additional applications for the re-engineered maser that include more sensitive medical scanners; chemical sensors for remotely detecting explosives; advanced quantum computer components; and better radio astronomy devices for potentially detecting life on other planets. Our next step is to provide a miniaturised benchtop demonstrator instrument capable of addressing these applications. This is important both to allow a transition from just studying room-temperature masers into actually using room-temperature masers, and as a step towards widespread use of these devices in other research labs and in industry. It is our experience and indeed that of colleagues engaging with industrial partners, that it is essential that we provide a proof of principle instrument.

Quantum mechanics is both mysterious and powerful. At a very fundamental level our world works in a bizarre way that defies our common sense. Tapping in to this bizarre world provides a rich avenue to improve our understanding of the foundations of physics and harnessing this behaviour for the development of powerful new quantum technologies. This project will establish a UK-first facility--the Quantum Science and Device Facility (QSDF)--for researchers to tap into key aspects of the quantum world. More specifically, to cool scientific samples to near absolute zero in temperature and study the quantum properties of materials, superconductors, light-matter interactions, and importantly hybrid devices that utilize the advantages that each of these types of systems provide. We will work with national and international collaborators and partners to realise this vision and we will make the facility available to both empower and harness the potential of the wider UK community. Key examples of the science that can emerge from this facility include: laying the foundations for powerful new types of quantum computers comprising superconducting circuits, and making steps towards a "quantum internet" by developing a microwave-to-optical converter that can link distant superconducting quantum computers via optical fibre.