School of Physics - Theses

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    Moments-Based Corrections to Variational Quantum Computation
    Jones, Michael Alexander ( 2020)
    Quantum Computing offers the potential to efficiently solve problems for which there are no known, efficient classical solutions such as factoring of semi-prime numbers and simulation of quantum- mechanical systems. This work considers a novel moments-based adaptation of the Variational Quantum Eigensolver (VQE), one of the leading candidates for demonstrating quantum supremacy. The method for improving the estimated ground state energy of a quantum system, obtained using the Variational Quantum Eigensolver, is presented and tested for Heisenberg model systems using IBM’s superconducting quantum devices. The method is based on the application of a Lanczos expansion technique based on the computation of Hamiltonian moments and is found to offer better accuracy than conventional VQE for most cases considered, allowing for a simpler trial state and offsetting the effects of noise.
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    Electrical Characterisation of Ion Implantation Induced Defects in Silicon Based Devices for Quantum Applications
    Duan, Aochen ( 2020)
    Quantum devices that leverage the manufacturing techniques of silicon-based classical computers make them strong candidates for future quantum computers. However, the demands on device quality are much more stringent given that quantum states can decohere via interactions with their environment. In this thesis, a detailed investigation of ion implantation induced defects generated during device fabrication in a regime relevant to quantum device fabrication is presented. We identify different types of defects in Si using various advanced electrical characterisation techniques. The first experimental technique, electrical conductance, was used for the investigation of the interface state density of both n- and p-type MOS capacitors after ion implantation of various species followed by a rapid thermal anneal. As precise atomic placement is critical for building Si based quantum computers, implantation through the oxide in fully fabricated devices is necessary for some applications. However, implanting through the oxide might affect the quality of the Si/SiO_2 interface which is in close proximity to the region in which manipulation of the qubits take place. Implanting ions in MOS capacitors through the oxide is a model for the damage that might be observed in other fabricated devices. It will be shown that the interface state density only changes significantly after a fuence of 10^13 ions/cm^2 except for Bi in p-type silicon, where significant increase in interface state density was observed after a fuence of 10^11 Bi/cm^2. The second experimental technique, deep level transient spectroscopy, was used to study the defects in the substrate of Si after ion implantation. As Er has the potential of interfacing electrical and optical properties of Si based quantum computers, it is important to know what defects will be present after the implantation because of its large atomic mass. H and Er implantation damages were compared to demonstrate the more complex defect evolution for Er implantation. Although defects were still present after a 400 C anneal, the concentration was reduced by at least one order of magnitude. The last experimental technique, charge pumping, was used on MOSFETs to study the interface state density directly in device structures that can be directly used in, for example, magnetic resonance and quantum sensing applications. Charge pumping has the potential of allowing measurement and manipulation of both electronic and magnetic properties of the interface defects and defects in the MOSFET channel. For such applications it may be necessary to operate the device close to absolute zero temperature. The work presented here represents a first step towards device and technique development with the ultimate aim of pushing measurements to mK temperatures where quantum device operations typically operate.
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    Flexible electrodes for neural recording, stimulation and neurochemical sensing
    Hejazi, Maryam Alsadat ( 2020)
    This thesis focuses on the development of implantable neural interfaces to perform multifunctional neural recording, neural stimulation and biochemical sensing. Neural interfacing devices using penetrating electrodes have emerged as an important tool in both neuroscience research and medical applications. These implantable electrodes enable communication between man-made devices and the nervous system by detecting and/or evoking neuronal activities. Recent years have seen a rapid development of electrodes fabricated using flexible, ultrathin microwires/microfibers. Compared to the arrays fabricated with rigid materials and larger cross sections, these microwires/microfibers have been shown to reduce foreign body response after implantation, with improved signal-to-noise ratio for neural recording and enhanced resolution for neural stimulation. Carbon fibers (CFs) are considered for implant into particular tissue types since they have small size, cause less tissue damage, and are flexible. CF recording electrodes have shown promise as recording electrodes and have the properties necessary to form sensing electrodes. Micron-scale electrodes such as CFs are expected to evoke localized neural responses due to localized electric fields. CFs are traditionally used with fast-scan cyclic voltammetry to study rapid neurotransmitter changes in vivo and in vitro, as they allow real-time detection of catecholamines with high sensitivity and selectivity. However, they possess narrow usable voltage range, which limits their application for neural stimulation. Additionally, surface fouling occurs with certain neurochemicals potentially obstructing further neurotransmitter adsorption onto the electrode surface. Therefore, they need to be coated with other materials to boost their electrochemical properties for neural stimulation. In this thesis, diamond and diamond-like materials, in particular nitrogen doped ultrananocrystalline diamond (NUNCD) hybrid and boron doped carbon nanowall (B-CNW) are considered as coatings for CFs to enhance properties towards neural interface applications. A focus is finding acceptable properties for recording, stimulation and neurochemical sensing. Novel fabrication techniques were developed to deposit the films onto the surface of CFs. Firstly, the surface of CFs was amine-functionalised and covalent bonds were formed with oxygen terminated nanodiamonds. Films were grown on the treated/seeded fibers using plasma-assisted chemical vapor deposition. To fabricate single fiber electrodes, individual fibers were insulated with capillary glass with 100 micrometer of fiber exposed. The physical and chemical properties of NUNCD hybrid and B-CNW were characterized and studied. The results from electrochemical characterization, in conjunction with both in vitro and in vivo assessments, suggest that these electrodes offer a highly functional alternative to conventional electrode materials for both recording and stimulation, yielding safe charge injection capacities up to 25.08 +-12.37 mC/cm2. To test the capability of electrodes for neural stimulation in vitro, explanted wholemount rat retina was used. The electrodes could elicit localized stimulation responses in the explanted retina. These electrodes with micron -scale cross sections have the potential to improve the spatial resolution for stimulation while minimizing axon bundle activation. In vivo and in vitro single-unit recording showed that the electrodes could detect signals with high signal-to-noise ratios up to 8.7. NUNCD hybrid coated CFs were able to electrochemically detect dopamine with high sensitivity and selectivity. Such electrodes are needed for the next generation of miniaturized, closed-loop implants that can self-tune therapies by monitoring both electrophysiological and biochemical biomarkers.
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    Resonant Leptogenesis and Quark-Lepton Unification with Low-Scale Seesaws
    Dutka, Tomasz ( 2020)
    The seesaw mechanism, where a hierarchy exists between the moduli of different entries of a mass mixing matrix, is a simple and theoretically attractive explanation for the observed large hierarchy between the neutral- and charged-fermion masses of the Standard Model. The simplest neutrino mass seesaw predicts that, upon diagonalisation, the physical mass states will either all be Majorana or all form pseudo-Dirac pairs. Non-minimal variants of this seesaw often generate a hybrid scenario with the physical mass states being a combination of both Majorana and pseudo-Dirac pairs. Such models often predict unique phenomenology and also allow for much lower mass scales of new physics. This thesis explores the implications such non-minimal variants can have beyond the simple generation of neutrino mass, particularly the possible role they may have in explaining the observed matter-antimatter asymmetry as well as implications for particular models of quark-lepton unification. Chapter 1 reviews the current experimental evidence for neutrino mass and discusses some possible tree-level origins. The matter-antimatter asymmetry is introduced and the conditions necessary for the dynamical generation of this observed asymmetry are reviewed. The idea of thermal leptogenesis is outlined as a simple mechanism for generating an asymmetry dynamically at an epoch between the the period of reheating and the electroweak phase transition of the early universe. Finally, the idea that quarks and leptons are related by hidden symmetries are discussed with a particular emphasis on the quark-lepton unifying Pati-Salam gauge group. In Chapter 2 we consider the leptogenesis implications for the Standard Model extended by two gauge-singlet fermions for each generation of charged lepton. We focus on the possibility of resonant scenarios without the need for inter-generational mass degeneracies and therefore do not require a possible flavour symmetry origin. The possible connection between neutrino parameters measureable in low-energy experiments and the generation of a matter-antimatter asymmetry is explored. In Chapter 3 we extend the analysis of the previous chapter and highlight how a flavour symmetry can allow for leptogenesis in a much wider region of parameter space for the extended seesaw used in \Cref{Chapter2}. The benefits of this extended seesaw, compared to the minimal seesaw scenario, when the proposed flavour symmetry is included are discussed and implications for low-energy flavour-violation experiments are explored. In Chapter 4 different possible Pati-Salam models are discussed with an emphasis on the connection between the scale of Pati-Salam breaking and the scale of heavy neutrino masses. Models allowing for the breaking scale to occur close to the electroweak scale are introduced. The dominant experimental probe of Pati-Salam is discussed and the current limits on the scale of breaking are calculated. Simple extensions of this model are proposed which both break an undesired mass degeneracy in the theory and allow for a significant reduction in the experimental limits on Pati-Salam breaking. A thorough analysis of the possible allowed parameter space in which both of these effects occur is explored and any possible connection to the symmetries of the theory is made. Chapter 5 briefly concludes.
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    Models of radiative neutrino mass and lepton flavour non-universality
    Gargalionis, Johnathon James ( 2020)
    This thesis presents a series of original studies exploring the space of neutrino-mass models, and the connection that a class of these models might have with the recently purported violations of lepton flavour universality measured in $B$-meson decays. We begin by describing and implementing an algorithm that systematises the process of building models of Majorana neutrino mass starting from effective operators that violate lepton number by two units. We use the algorithm to generate computational representations of all of the tree-level completions of the operators up to and including mass-dimension eleven, almost all of which correspond to models of radiative neutrino mass. Our study includes lepton-number-violating operators involving derivatives, updated estimates for the bounds on the new-physics scale associated with each operator, an analysis of various features of the models, and a look at some examples. Accompanying this work we also make available a searchable database containing the catalogue of neutrino-mass models, as well as the code used to find the completions. The anomalies in $B$-meson decays have known explanations through exotic scalar leptoquark fields. We add to this work by presenting a detailed phenomenological analysis of a particular scalar leptoquark model: that containing $S_{1} \sim (\mathbf{3}, \mathbf{1}, -\tfrac{1}{3})$. We find that the leptoquark can accommodate the persistent tension in the ratios $R_{D^{(*)}}$ as long as its mass is lower than approximately $\SI{10}{\TeV}$, and show that a sizeable Yukawa coupling to the right-chiral tau lepton is necessary for an acceptable explanation. Agreement with the measured $R_{D^{(*)}}$ values is mildly compromised for parameter choices addressing the tensions in the $b \to s$ transition. The leptoquark can also reconcile the predicted and measured value of the anomalous magnetic moment of the muon, and appears naturally in models of radiative neutrino mass. As a representative example, we incorporate the field into a two-loop neutrino mass model from our database. In this specific case, the structure of the neutrino-mass matrix provides enough freedom to explain the small masses of the neutrinos in the region of parameter space dictated by agreement with the anomalies in $R_{D^{(*)}}$, but not in the $b \to s$ transition. In order to address the shortcomings of the $S_{1}$ scenario, we construct a non-minimal model containing the scalar leptoquarks $S_{1}$ and $S_{3} \sim (\mathbf{3}, \mathbf{3}, -\tfrac{1}{3})$ along with a vector-like quark, necessary for lepton-number violation. We find that this new model permits a simultaneous explanation of all of the flavour anomalies in a region of parameter space that also reproduces the measured pattern of neutrino masses and mixing. A characteristic prediction of our model is a rate of muon--electron conversion in nuclei fixed by the $b \to s$ anomalies and the neutrino mass. The next generation of muon--electron conversion experiments will thus potentially discover or falsify our scenario. We also present a general overview from our model database of those minimal radiative neutrino-mass models that contain leptoquarks that are known to explain the anomalies in $R_{D^{(*)}}$ and the $b \to s$ transition. We hope that our model database can facilitate systematic analyses similar to this, perhaps on both the phenomenological and experimental fronts. We conclude by presenting a study of the diphoton decay of a scalar $\mathrm{SU}(N)$ bound state, motivated by the 2016 \SI{750}{\GeV} diphoton excess.
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    Pulsar glitches and superfluid dynamics in neutron stars
    Howitt, George Alec William ( 2020)
    Glitches are sudden jumps in the spin frequency of pulsars that occur at random times and over several orders of magnitude in size. One popular theory holds that glitches are caused by differential rotation between the neutron star crust and a superfluid component in the interior. This implies that glitches can be used to study the dense nuclear matter inside neutron stars, testing a regime of physics inaccessible to present-day laboratory experiments or other electromagnetic observations. In the vortex avalanche model of pulsar glitches, the angular momentum of the superfluid is determined by the configuration of an array of quantized vortices which pin to impurities in the interior. As the star spins down, individual vortices unpin and move outwards, triggering unpinning in other nearby vortices leading to an avalanche. The angular momentum lost by the vortices as they move outward is transferred to the crust, which causes it to spin up. This thesis tests the superfluid model of pulsar glitches using hydrodynamic simulations of glitch recovery, statistical analysis of astronomical glitch data and N-body point vortex simulations of avalanches in an idealised neutron star model. Following a glitch, pulsars often have a lengthy recovery period of weeks to months, which is a key piece of evidence for the presence of a superfluid phase inside neutron stars. We perform simulations of glitch recovery using a pseudo-spectral Navier-Stokes-like solver. We model a neutron star as a two component superfluid consisting of a viscous proton-electron plasma and an inviscid superfluid neutron condensate in a spherical Couette geometry. The two fluid components are coupled through mutual friction. We prepare the system in a state of differential rotation between the core and the outer crust and examine the response of the outer boundary to glitches induced by instantaneously changing the angular velocity of the boundaries and by recoupling the fluid interior. We find that with strong mutual friction the characteristic glitch recovery time scale decreases by as much as a factor of three. For glitches originating in the fluid, strong mutual friction decreases the maximum spin up by a factor of up to five. These effects may be partially responsible for the diversity of glitch recoveries observed in the pulsar population, which vary from rapid, complete recoveries to slow partial recoveries or step changes in the spin frequency with no observed change in the spin down rate. The strength of mutual friction depends on where in the star a superfluid phase exists, so these results may allow future observations to constrain the star's internal structure. The vortex avalanche model of glitches is similar to other non-equilibrium systems in nature such as sandpiles, earthquakes and solar flares. Such systems are often studied in the paradigm of self-organized criticality (SOC), a hallmark of which is scale invariant size probability density functions (PDFs) and exponential waiting time PDFs. We perform a statistical study of the size and waiting time PDFs for the five most prolific glitching pulsars using the non-parametric kernel density estimator. This work complements previous parametric studies of glitches, which typically fit the PDFs to known distributions such as power laws, Gaussian or log-normal distributions. Two objects, PSR J1740-3015 and the Crab pulsar PSR J0534+2200, appear to have exponential waiting time PDFs and scale-invariant size PDFs over several decades. Two other objects, PSR J0537-6910 and the Vela pulsar PSR J0835-4510 have quasiperiodic size and waiting time PDFs, typical of fast-driven SOC systems. One object, PSR J1341-6220, appears to exhibit hybrid behaviour. We test the ability of the kernel density estimator to resolve multimodality in synthetic data drawn from a composite Gaussian distribution (which is qualitatively similar to the waiting time PDF in J1341-6220), and find that the small number of glitches observed in this object (N = 23) makes confirmation of multimodality in the PDFs difficult. In order to study the non-equilibrium dynamics of the vortex avalanche theory of glitches, it is useful to have an idealised model which can make falsifiable predictions about the properties of glitches, such as PDFs of sizes and waiting times, correlations between these observables, and the dependence of the PDFs on the internal parameters of the model. Previous work with Gross-Pitaevskii simulations has been unable to study systems larger than ~100 vortices, far from the ~10^18 vortices in neutron stars. With such small numbers of vortices, it is impossible to resolve the dynamics over multiple orders of magnitude. We develop a mathematical model for simulating the motion of point vortices in two dimensions under the influence of deceleration, dissipation, and pinning. We describe a numerical solver for this model, which uses an N-body method to compute the vortex velocities and an adaptive time step scheme for time evolution. We present the results of numerical experiments validating the method, including stability of a vortex ring and dissipative formation of an Abrikosov array. We then perform simulations of 1000-5000 vortices with a wide range of values for the strengths of dissipation and pinning, pinning site density and deceleration of the container. Vortex avalanches occur routinely in the N-body simulations, when chains of unpinning events are triggered collectively by vortex-vortex repulsion, consistent with previous, smaller scale studies using the Gross-Pitaevskii equation. The PDFs of the avalanche sizes and waiting times are consistent with both exponential and lognormal distributions. We find weak cross-correlations between glitch sizes and waiting times. These correlations are consistent with astronomical data and meta-models of pulsar glitch activity as a state-dependent Poisson process or a Brownian stress-accumulation process, and inconsistent with another popular alternative, a threshold-triggered stress-release model with a single, global stress reservoir. The spatial distribution of the effective stress within the simulation volume is analysed before and after a glitch.We find that stress is distributed homogeneously throughout the system and remains near the critical threshold both before and after glitches. This implies that there is no 'memory' in the system; glitches do not significantly reduce the global or local stress. This is consistent with the lack of strong cross-and-auto correlations between glitch sizes and waiting times in the simulations and pulsar data.
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    Diamond Quantum Sensing in Biological Systems
    McCoey, Julia Madelaine ( 2020)
    Biological discovery is fuelled by technological advances. As a new process is developed, a period of exploration tests the waters to uncover what the novel technology can reveal. This thesis presents the application of quantum sensing with negatively-charged nitrogen vacancy (NV) centres in diamond to real biological systems and questions. NV sensing provides a means to probe systems, including biosystems, in ways unavailable with other techniques. This is most evident in the NV’s magnetic sensitivity, along with a collection of attributes that lend it to biological settings. Many questions about biomagnetism remain unanswered, and the advent NV sensing affords a new avenue to explore these questions. In this thesis, we begin by establishing the techniques and capabilities of NV magnetic imaging in diamond. An introduction to magnetometry precedes a description of diamond, the properties of the NV centre, and quantum measurement protocols. We then dive into an animal model of iron biomineralisation, a sea mollusc with extraordinary teeth. Biomineralisation is an area of current interest that has previously received little attention from the angle of its intrinsic magnetic properties. Next, we see how nitrogen vacancy sensing can be applied to the improvement of magnetic tools used in the biosciences. These tools are seeing an explosion of new activity across multiple disciplines, so ways to evaluate them will prove valuable. Then, we examine the enigmatic mechanism behind animal magnetoreception. A remarkable sense known to be possessed by many disparate animal species, magnetoreception remains a near complete mystery. Finally, we consider the challenges and limitations of diamond-based temperature sensing in biological systems. This interdisciplinary endeavour has brought about exciting results including the first subcellular magnetic profiling of a eukaryotic system, vector magnetic images of developing biominerals, new protocols for the assessment of magnetic materials and avenues for new bioassays, and a window to a recently-discovered organelle with a suggested role in animal magnetoreception. With the current trajectory of quantum sensing with NV centres in diamond, the future for biological discovery looks bright.
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    Observational methods towards constraining the chemical evolution of galaxies
    Cameron, Alex James ( 2020)
    Understanding the array of physical processes that have shaped galaxy assembly remains one of the most fundamental pursuits in astrophysics. Gas in galaxies is enriched with heavy elements via stellar nucleosynthesis, but chemical abundances (``metallicity'') are also shaped by galaxy-scale processes including gas accretion, feedback-driven outflows, radial gas flows, interactions, and mergers. Metallicity measurements therefore afford one of our most powerful observational probes of galaxy evolution. In this thesis I explore the performance of observational methods for constraining (i) gas-phase metallicity in galaxies, and (ii) host dark matter halo masses of galaxies; the latter of which is critical to the physics of gas flows due to its contribution to the gravitational potential well of galaxies. A particular focus is the improved understanding of systematic uncertainties near instrumental limits, which will be vital to maximise the impact of surveys conducted with future facilities. Galaxy clustering is an efficient approach for drawing statistical connections between galaxies and their host dark matter haloes, however traditional methods are challenging to apply at z > 2 where imaging survey volumes are limited. I instead apply a counts-in-cell approach to photometric z ~ 2 candidates from a random-pointing Hubble Space Telescope survey, showing mean counts of N > ~5 per field are capable of constraining the large scale galaxy bias. The James Webb Space Telescope will achieve comparable number counts out to z ~ 8, and thus a similar JWST survey could place novel constraints on the halo masses of galaxies in the epoch of reionization. Global metallicities in low-mass galaxies afford important constraints on the impact of feedback-driven outflows on galaxy evolution. However at high-z, obtaining the requisite emission line measurements is observationally challenging. I use Keck/MOSFIRE spectroscopy to explore prospects for extending z ~ 1 - 2 metallicity measurements to lower masses. I find the dominant source of uncertainty arises from reduced number of emission lines as opposed to lower signal-to-noise, even at the detection limit. JWST/NIRSpec will revolutionise high-z metallicity studies due to the large suites of emission lines it will be able to assemble. Electron temperatures (T_e) measured with auroral lines are an important baseline in metallicity studies. However the faintness of auroral lines has hitherto limited spatially resolved T_e studies. I report two separate studies based on mapping auroral lines in integral-field spectroscopy (IFS) of low-z galaxies. Measurements of auroral lines in the SAMI Galaxy Survey afford new insights into the effects of ionisation parameter variations on recovered metallicity gradients. Applying these principles to Keck/KCWI IFS data of an edge-on disk galaxy, I measure an extra-planar temperature gradient and present preliminary evidence for extra-planar metallicity variations.
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    Towards Nanophotonic All-optical Image Processing
    Wesemann, Lukas ( 2020)
    The processing of spatial information, including images, is fundamental in modern scientific, industrial and medical applications. Some imaging techniques rely on amplitude information contained in a wavefield and permit conversion of optical information into electronic signals through conventional integrated photodetector technology and subsequent digital processing. The ever increasing complexity and volume of data that often needs to be processed in real-time and with low energy consumption in applications such as satellite imagery, autonomous vehicles or object and face recognition pushes current electronic systems to its limits. Other situations utilize the extraction of polarization or phase information from a wavefield which commonly requires the use of optical image processing technology. The visualization of phase information underpins for example widely employed techniques to enhance image contrast in live biological cells. Conventional optical processing approaches, however, typically involve expensive and bulk-optical components thereby limiting their potential to be involved in next-generation compact optical systems. These constraints on current electronic and optical processing technology require the development of new solution approaches. Ultra-compact, analogue optical solutions that enable real-time processing of spatial information carry potential to circumvent conversion of optical to electronic signals and the associated digital computation while simultaneously avoiding bulk-optical components. The significant progress in micro- and nanofabrication over the last decades has enabled researchers to create artificial materials with unprecedented optical characteristics including photonic crystals, thin-film systems and optical metasurfaces. Recently these systems have gained considerable scientific attention for the implementation of analogue spatial computation devices and have been applied to all-optically perform mathematical operations including differentiation and integration on optical images. In particular approaches that enable accessing and manipulating the Fourier content of a wavefield in the object-plane carry vast potential for the development of flat optical image processing solutions. The main objective of this work is to further our understanding of ultra-compact all-optical image processing in general, and to develop specific implementation approaches utilizing nanophotonic structures. Here the conception, modelling, fabrication and characterization of three fundamentally different approaches to nanophotonic image processing in the object plane are presented for the first time. Firstly, metal-insulator-metal thin-film absorbers are investigated for the first time as reflective image processing devices. Secondly, the excitation of subradiant modes on plasmonic trimer metasurfaces is exploited to perform all-optical spatial frequency filtering in reflection. Finally, plasmonic resonant waveguide gratings are investigated as compact transmitting spatial frequency filters. The implemented solutions are applied as high-pass spatial frequency filters to demonstrate all-optical edge-detection in amplitude images and the visualization of phase gradients in optical wavefields. Furthermore proof-of-concept application of the investigated structures to image processing of biological samples is demonstrated. The results of this thesis contribute to the advancement of our understanding of nanophotonic systems for the processing of spatial information and demonstrate their significant potential to be integrated in next-generation optical systems.
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    Donor activation and isotopic enrichment of silicon via ion implantation for quantum computing
    Holmes, Danielle ( 2020)
    Quantum computers are set to revolutionise technology by harnessing the immense promise of quantum mechanics, the law governing nature on the atomic scale, to enable a dramatically increased efficiency for certain algorithms over their classical counterparts. By storing and manipulating information on quantum bits (qubits), which can exist in a superposition of 0 and 1 at the same time and can be entangled with each other, instead of classical bits, which are strictly 0 or 1, certain problems that are intractable with classical computation can be solved. To realise a qubit, a quantum system that exists in two or more states, such as a spin in a magnetic field, is required. Group V donors in silicon (Si) are promising qubit candidates that can store quantum information in both the spin of the donor nucleus and the donor electron that it binds by the Coulomb potential. Si offers an ideal platform due to its isotopic composition of predominantly spin-zero nuclei (over 92% is 28Si with nuclear spin I=0), that can provide a noise-free host lattice, and the wealth of knowledge accumulated in the microelectronics industry. The most versatile method for introducing donors in Si is ion implantation, a foundational technique of the information technology industry that has already demonstrated the production of long-lived phosphorus (P) donor qubits. This method is explored in this thesis. The bismuth (Bi) donor offers some useful properties for quantum devices, such as an increased quantum memory, clock transitions and the potential to couple to superconducting flux qubits. To fabricate a quantum device that employs Bi, it is necessary to implant and activate a Bi donor in Si. Here, the optimum implantation and thermal annealing strategy is determined to maximise the operational yield of near-surface Bi donor qubits by repairing the Si crystal damage and electrically activating the donor, evidenced by the measurement of Bi donor electron spin resonance. A further critical issue in donor qubit fabrication is the depletion of the nuclear spin-1/2 29Si isotope to extend coherence times, which would be beneficial to be performed routinely. Accordingly, a method of isotopically enriching a surface layer of natural Si via sputtering during the high fluence implantation of 28Si- ions was developed. This technique increases the accessibility of producing spin-free 28Si material by requiring only a conventional ion implanter and naturally abundant sources. The successful recrystallisation of this 28Si layer and the demonstration of increased coherence times for implanted P donors make this a promising technique for integrating into the fabrication of implanted donor qubits. Finally, the measurement of the full extent of the 29Si depletion on the coherence time requires a low concentration of donors implanted into this ~100 nm thick surface layer of 28Si. Therefore,a high sensitivity technique capable of probing a small number of spins is essential. This challenge is addressed by the design and implementation of a low-temperature electrically detected magnetic resonance (EDMR) system, capable of measuring spin transitions of donor electrons in Si with a sensitivity at least 5 orders of magnitude greater than for conventional electron spin resonance systems. In future, this will allow for the coherence times of donors implanted into our enriched 28Si layers to be determined from the linewidth of EDMR signals. This thesis lays the foundations for exploiting Bi donor clock transitions in qubit devices and addresses the challenge of providing an isotopically enriched 28Si matrix for donor qubits that is shown to extend qubit coherence times and thus makes progress towards the scalable fabrication of a donor spin quantum computer.