Quantum matter, quantum optics and photonics
Much of the research of our group focuses on exploring and exploiting the interaction of light with matter. We are involved in exciting research around spintronics, quantum electrodynamics and hybrid circuits which we explore using our various laboratories.
The use of light to communicate and process information is widely recognised as the technology that will drive innovations in the 21st century across a wide range of areas, from information technology, energy and sensing, to healthcare. So far, control of light flow has been achieved by carefully and periodically structured materials, which can bend light, slow it down and stop if for a short time, to allow for the processing steps to take place. Due to recent advances in theoretical, computational and nano-fabrication capabilities we are no longer restricted to well-defined periodic structures. Instead we can construct complex systems made of apparently random patterns, which when suitably designed, can lead to performances superior to those offered by conventional photonic systems.
Our team based in the Advanced Technology Institute is leading the development of hyperuniform and local self-uniform disordered nanophotonic materials, novel classes of photonic structures in which structural correlations and disorder are accurately controlled with the aim to control light flow, enhance light emission, and construct novel types of nanophotonic devices.
As well as theoretical work, we have a vibrant experimental programme, much of which is focused on research with ion beams, which provide the only quantum technology fabrication methodology that seamlessly integrates with existing microelectronic processes and allows for large-scale production involves the incorporation of single impurity qubits via implantation. This technique promises qubit arrays large enough for error correction and the potential for mass production of identical devices. Fully developed deterministic single ion implantation is crucial to exploit the full potential of impurity-based QT for scale-up.
Implantation of single qubit atoms in silicon presents a viable solution. However, current research primarily focuses on the stochastic incorporation of impurities, with only limited control over placement using masks or focused beams. Defect complexes in diamond have shown early success in quantum computing by demonstrating qubits at room temperature. Presently, ISI is not utilised for nitrogen-vacancy (NV) centres in diamond, as nitrogen is a naturally occurring impurity in diamond, and implantation tends to produce vacancies that combine with pre-existing nitrogen atoms.
Deterministic ISI can generate defect complexes in silicon carbide, where photonic devices for quantum networks have already been demonstrated using focused ion beams, albeit without precise control over the number of implanted ions. This technology could also be expanded to include rare earth impurities for quantum communications with further ion source development. While it is feasible to locate a random defect complex and then construct device architecture around it, a deterministic approach to producing colour centres would significantly enhance commercial manufacturing yields.
Quantum optical in hyperuniform disordered materials
By exploiting the intrinsic statistical isotropy of the electromagnetic properties of the hyperuniform disordered materials, we are exploring new phenomena in optically active hyperuniform disordered systems. This isotropic scattering occurring over a finite range of frequencies facilitates a variety of photon transport regimes, ranging from ballistic-like to diffusive transport and even Anderson localisation.
Our recent work has exploited hyperuniform disordered designs of slab architectures, use of embedded quantum dots for feeding the hyperuniform resonances, and near-field hyperspectral imaging with sub-wavelength resolution to explore the transition from localisation to diffusive transport and to demonstrate the presence of both Anderson-localised modes and confined cavity modes with high-quality factors, with small footprint, intrinsically reproducible and resilient to fabrication-induced disorder, paving the way for a novel photonic platform for quantum applications.
Energy harvesting and thermal radiation management
The ability of micro and nanostructured photonic materials to facilitate significant alteration of thermal radiation processes is receiving considerable attention due to both the scientific relevance and potential for technological applications.
Our research in this area is focused on the development of hyperuniform disordered nanophotonic metasurfaces, a novel type of structuring in which correlations and disorder are accurately controlled for achieving solar-thermal radiation conversion and management.
We have initiated a synergistic theoretical, computational and experimental approach to elucidate the fundamental correlation between the geometric and topological characteristics of the hyperuniform structures and their angle- and frequency-selective properties and to exploit the ability of nanostructured photonic materials to facilitate significant alteration of thermal radiation processes. This effort is supported by our recent demonstration of record-breaking efficiency in hyperuniformly textured thin-film silicon solar cells.
Structural colour and biomimetics
Studies of fish scales, insect coatings, mammal skin and bird feathers have revealed that membranes of living cells and intracellular organelles exhibit the capacity to self-organise into a variety of complex, nano to mesoscale structures similar to those in block-copolymers and other soft condensed matter systems. An accurate description of the colour-producing biological structures is essential for understanding their optical functionalities and can be directly exploited to the development and production of biomimetic devices that leverage comparable physical mechanisms.
Our research on photonic networks by their local self-uniformity has enabled a direct classification of advanced optical functionalities in materials as diverse as iridescent opals and the brilliantly white chaotic structure in Cyphochilus beetle scales, encompassing quasicrystals and glasses en route.
The local-self uniformity metric we have introduced not only sheds light on the regularity of fixed valency networks, but also establishes a direct connection between the structuring present in a myriad of photonic materials found in the natural world, and the advanced optical functionalities including structural colour. It can prove itself very useful in designing photonic structures with various functionalities, including spectral and directional control over the absorption of light and engineering structural colour.
Direct write of superconducting quantum interference devices with focused ion beams
The longest running activity within the group linking ion beams to quantum technologies is the fabrication of superconducting quantum interference devices (SQUIDs) via a direct write process using focused ion beams.
SQUIDs are some of the most sensitive detectors ever fabricated and have a wide range of applications encompassing quantum, electronic, magnetic, thermometry photon-detection and more. For more than 16 years we have been fabricating SQUID devices using these methods and have had a partnership with the National Physical Laboratory in this activity throughout this time.
Advancements in THz non-linear optics using doped silicon
Our research has revealed that doped silicon exhibits an unprecedented non-linear optical coefficient, capable of photon manipulation at levels unseen in any other material.
This characteristic allows for the conversion of photons, akin to the process in green laser pointers where invisible near-infrared photons are transformed into visible light. Although requiring cryogenic temperatures, we are exploring the potential of this effect in specialised spectroscopy systems and other high-tech applications where cryogenic cooling is already utilised.
Magnetic field manipulation of quantum systems
Utilising magnetic fields as a non-invasive tool, we are able to intricately modify the energy states within electronic materials. This technique allows for the precise control of electron motion, facilitating the identification of key properties. For instance, we can fine-tune the energy levels of silicon donors to resonate with specific phonon modes, shedding light on the mechanisms of donor relaxation.
Understanding these interactions may lead to strategies to enhance quantum state lifetimes, thereby improving the efficiency of quantum computing elements.
Unveiling quantum interactions: donor bound exciton spectroscopy
Our research has successfully utilised donor bound exciton spectroscopy to discern the intricate hyperfine interactions between electrons and nuclei in implanted impurities.
This achievement not only demonstrates precise quantum control capabilities crucial for quantum computing but also moves forward our current investigations into how device fabrication-induced strains can influence these sensitive quantum systems.
Lateral solid-phase epitaxial regrowth for precision impurity positioning
This research applies lateral solid-phase epitaxial regrowth to improve the placement of impurities in semiconductors. Our methodical approach aims to refine single ion implantation accuracy, potentially advancing quantum computing applications by ensuring precise impurity positioning.
Single ion implant detection using ion beam induced charge
Our research has achieved near-perfect efficiency in detecting single ion implantation events within silicon-on-insulator (SOI) devices.
This breakthrough is critical for investigating the spatial precision of single ion implants using focused ion beam systems, laying the groundwork for scalable production of solid-state quantum computers.
Advanced strain engineering in semiconductor membranes
Our research introduces a refined process using ion beam irradiation to precisely engineer strain in single-crystal silicon membranes by controlling the degree of amorphisation around the active crystal.
This method offers significant potential for advancing photonics and quantum technologies, enabling enhanced performance in germanium-based optoelectronics and precise manipulation of material quantum properties via strain introduction/ cancelling without creating spin impurities in the device region.
High-resolution impurity detection with synchrotron X-ray fluorescence spectroscopy
In recent research, we have utilised synchrotron X-ray fluorescence spectroscopy to detect impurities down to just a few atoms.
Our findings reveal that current synchrotron capabilities can pinpoint hundreds of these impurities, and with anticipated improvements to higher intensity synchrotrons, the detection of a single atom may soon be within reach.
Isotopic purification through ion beam deposition
Our team is at the forefront of developing a specialised ultra-low energy ion-beam system designed to deposit mass-selected ions gently onto substrates. This technique promises a new method for creating isotopically-pure layers, essential for qubit stability in quantum computing.
Focusing on materials like 28Si and direct-bandgap 74Ge120Sn, the tool is poised to not only construct layers with exact isotopic compositions but also to fine-tune internal strains, offering a leap forward in material control and quantum device performance.
Isotopic purification through layer exchange
Our team is pioneering a unique isotopic enrichment technique with the potential to use conventional industrial CMOS implanters, to produce "quantum grade" 28Si layers essential for quantum computing.
This innovative implant-based layer exchange process adapts established methods from the solar cell industry, substituting a step with the implantation of 28Si into aluminium layers, thereby creating high-purity silicon necessary for next-generation quantum devices.
Single photon emitters engineered through ion implantation
We are exploring the possibilities of using ion implantation to create single photon sources (SPS)which are crucial for secure communications and advanced quantum computing systems.
These can be formed by the implantation of impurities such as rare earth erbium, or the creation of defect centres.