arXiv subjects

Alastair Basden

Publications and source records attributed to Alastair Basden.

At least 19 recordsLinked to original sources

arXiv2026

Halo mass functions in mixed cold and fuzzy dark matter models

We investigate the impact of mixed cold and fuzzy dark matter (MDM) cosmologies on the halo mass function (HMF) using numerical simulations performed with the AxiREPO framework. We consider models in which an ultralight axion-like component with mass $m =10^{-24.5} \mathrm{eV}$ constitutes a fraction $f \leq 0.3$ of the total dark matter. To enable consistent halo identification in mixed-species scenarios, we develop a grid-based halo-finding pipeline that combines the particle-based cold dark matter (CDM) and wave-like fuzzy dark matter (FDM) components into a unified density field. We find that FDM traces the large-scale CDM distribution while suppressing small-scale structure through wave interference effects, leading to a reduction in the abundance of low-mass haloes and modifying the HMF in a manner dependent on redshift and FDM fraction. Increasing the FDM fraction produces a systematic downward shift in the HMF and modifies its high-mass slope. Motivated by these trends, we introduce a phenomenological model that maps CDM HMFs to their MDM counterparts using a suppression function with parameters dependent on redshift and FDM fraction. This model reproduces the simulated HMFs within approximately 0.1 to 0.2 dex across the parameter space explored ($1 \leq z \leq 4$, $f \leq 0.3$). Our results provide a computationally efficient method for predicting structure formation in MDM cosmologies without requiring dedicated simulations for each parameter choice, and establish a framework for exploring the impact of MDM on cosmological structure formation.

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arXiv2026

Encoding strategies for quantum enhanced fluid simulations: opportunities and challenges

Quantum computing has emerged as a powerful potential accelerator for computational fluid dynamics (CFD), but whether this promise can be realized in practice depends on how fluid information is encoded on quantum hardware. This review provides an architecture-agnostic assessment of encoding strategies for quantum-enhanced fluid simulation, focusing on the trade-offs they impose on state preparation, measurement, boundary treatment, nonlinear dynamics, and temporal evolution. We examine the principal encoding paradigms used in the literature and relate them to representative quantum algorithms for fluid simulation. Through these examples, we show that encoding choices fundamentally shape both the algorithm itself and also the practical feasibility of quantum CFD. For example, highly compact encodings can offer attractive asymptotic advantages but might introduce severe bottlenecks in readout, state preparation, and nonlinear processing, whereas less compact representations may simplify interactions and improve compatibility with analog and near-term hardware. No single encoding is universally optimal, rather the most suitable choice depends strongly on the structure of the fluid problem, the computational objective and the constraints of the target quantum platform. We therefore argue that encoding should be treated as a primary design variable in quantum CFD and revisited iteratively throughout the design pipeline, as different algorithmic components interact and influence one another.

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arXiv2024

Integrating Quantum Algorithms Into Classical Frameworks: A Predictor-corrector Approach Using HHL

The application of quantum algorithms to classical problems is generally accompanied by significant bottlenecks when transferring data between quantum and classical states, often negating any intrinsic quantum advantage. Here we address this challenge for a well-known algorithm for linear systems of equations, originally proposed by Harrow, Hassidim and Lloyd (HHL), by adapting it into a predictor-corrector instead of a direct solver. Rather than seeking the solution at the next time step, the goal now becomes determining the change between time steps. This strategy enables the intelligent omission of computationally costly steps commonly found in many classical algorithms, while simultaneously mitigating the notorious readout problems associated with extracting solutions from a quantum state. Random or regularly performed skips instead lead to simulation failure. We demonstrate that our methodology secures a useful polynomial advantage over a conventional application of the HHL algorithm. The practicality and versatility of the approach are illustrated through applications in various fields such as smoothed particle hydrodynamics, plasma simulations, and reactive flow configurations. Moreover, the proposed algorithm is well suited to run asynchronously on future heterogeneous hardware infrastructures and can effectively leverage the synergistic strengths of classical as well as quantum compute resources.

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arXiv2024

Load Balancing For High Performance Computing Using Quantum Annealing

With the advent of exascale computing, effective load balancing in massively parallel software applications is critically important for leveraging the full potential of high performance computing systems. Load balancing is the distribution of computational work between available processors. Here, we investigate the application of quantum annealing to load balance two paradigmatic algorithms in high performance computing. Namely, adaptive mesh refinement and smoothed particle hydrodynamics are chosen as representative grid and off-grid target applications. While the methodology for obtaining real simulation data to partition is application specific, the proposed balancing protocol itself remains completely general. In a grid based context, quantum annealing is found to outperform classical methods such as the round robin protocol but lacks a decisive advantage over more advanced methods such as steepest descent or simulated annealing despite remaining competitive. The primary obstacle to scalability is found to be limited coupling on current quantum annealing hardware. However, for the more complex particle formulation, approached as a multi-objective optimization, quantum annealing solutions are demonstrably Pareto dominant to state of the art classical methods across both objectives. This signals a noteworthy advancement in solution quality which can have a large impact on effective CPU usage.

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arXiv2019

Focal Plane Tip-Tilt Sensing for Improved Single-Mode Fiber Coupling using a 3D-printed Microlens-Ring

Modern extreme adaptive optics (AO) systems achieving diffraction-limited performance open up new possibilities for instrumentation. Especially important for the fields of spectroscopy and interferometry is that it enables the prospect to couple light into single-mode fibers (SMFs). However, due to their small size, efficient coupling is very sensitive to the quality of the fiber alignment, beam drifts and higher-frequency tip-tilt aberrations caused by telescope mechanics and vibrations. These residual aberrations are not always sensed and corrected by the AO system, leading to unacceptable losses. This is particularly severe for the Extremely Large Telescopes, where their huge structure will mean vibrations increase and optimal AO solutions are even more difficult to implement. We have created a focal plane sensor to correct for residual aberrations by surrounding the SMF with six Multi-mode fibers (MMFs). On each of the MMFs sits a printed freeform lens, making up a six-element micro-lens ring to refract the light into these surrounding MMFs and thus minimizing light loss in the gap between the fiber cores. This means when the beam is near diffraction limited and centered almost all light couples to the SMF. When the beam is misaligned, it couples to the surrounding cores, which are read out by a detector and processed by the DARC software driving a tip-tilt mirror. Currently we are aiming to detect and correct only tip-tilt aberrations. However, choosing to surround the central fiber with six sensing locations potentially allows us to investigate higher order correction modes. Here we present the design and performance our prototype system. This has been designed for use with the iLocater fiber injection system at the LBT and can easily be scaled to larger telescopes. We present test results from the KOOL laboratory and initial integration with the iLocater instrument.

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arXiv2019

Efficient implementation of pseudo open loop control for adaptive optics on Extremely Large Telescopes

Closed-loop adaptive optics systems which use minimum mean square error wavefront reconstruction require the computation of pseudo open loop wavefront slopes. These techniques incorporate a knowledge of atmospheric statistics which must therefore be represented within the wavefront slope measurements. These pseudo open loop slopes are computed from the sum of the measured residual slopes and the reconstructed slopes that would be given if the deformable mirror was flat, generally involving the multiplication of an interaction matrix with actuator demands from the previous time-step. When using dense algebra, this multiplication is computationally expensive for Extremely Large Telescopes, requiring a large memory bandwidth. Here we show that this requirement can be significantly reduced, maintaining mathematical correctness and significantly reducing system complexity. This therefore reduces the cost of these systems and increases robustness and reliability.

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arXiv2018

ELT-scale Adaptive Optics real-time control with the Intel Xeon Phi Many Integrated Core Architecture

We propose a solution to the increased computational demands of Extremely Large Telescope (ELT) scale adaptive optics (AO) real-time control with the Intel Xeon Phi Knights Landing (KNL) Many Integrated Core (MIC) Architecture. The computational demands of an AO real-time controller (RTC) scale with the fourth power of telescope diameter and so the next generation ELTs require orders of magnitude more processing power for the RTC pipeline than existing systems. The Xeon Phi contains a large number (> 64) of low power x86 CPU cores and high bandwidth memory integrated into a single socketed server CPU package. The increased parallelism and memory bandwidth are crucial to providing the performance for reconstructing wavefronts with the required precision for ELT scale AO. Here, we demonstrate that the Xeon Phi KNL is capable of performing ELT scale single conjugate AO real-time control computation at over 1.0 kHz with less than 20 μs RMS jitter. We have also shown that with a wavefront sensor camera attached the KNL can process the real-time control loop at up to 966 Hz, the maximum frame-rate of the camera, with jitter remaining below 20 μs RMS. Future studies will involve exploring the use of a cluster of Xeon Phis for the real-time control of the MCAO and MOAO regimes of AO. We find that the Xeon Phi is highly suitable for ELT AO real time control.

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arXiv2018

Artificial guide stars for adaptive optics using unmanned aerial vehicles

Astronomical adaptive optics systems are used to increase effective telescope resolution. However, they cannot be used to observe the whole sky since one or more natural guide stars of sufficient brightness must be found within the telescope field of view for the AO system to work. Even when laser guide stars are used, natural guide stars are still required to provide a constant position reference. Here, we introduce a technique to overcome this problem by using rotary unmanned aerial vehicles (UAVs) as a platform from which to produce artificial guide stars. We describe the concept, which relies on the UAV being able to measure its precise relative position. We investigate the adaptive optics performance improvements that can be achieved, which in the cases presented here can improve the Strehl ratio by a factor of at least 2 for a 8~m class telescope. We also discuss improvements to this technique, which is relevant to both astronomical and solar adaptive optics systems.

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arXiv2018

The Durham Adaptive Optics Simulation Platform (DASP): Current status

The Durham Adaptive Optics Simulation Platform (DASP) is a Monte-Carlo modelling tool used for the simulation of astronomical and solar adaptive optics systems. In recent years, this tool has been used to predict the expected performance of the forthcoming extremely large telescope adaptive optics systems, and has seen the addition of several modules with new features, including Fresnel optics propagation and extended object wavefront sensing. Here, we provide an overview of the features of DASP and the situations in which it can be used. Additionally, the user tools for configuration and control are described.

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arXiv2016

Monte-Carlo modelling of multi-object adaptive optics performance on the European Extremely Large Telescope

The performance of a wide-field adaptive optics system depends on input design parameters. Here we investigate the performance of a multi-object adaptive optics system design for the European Extremely Large Telescope, using an end-to-end Monte-Carlo adaptive optics simulation tool, DASP, with relevance for proposed instruments such as MOSAIC. We consider parameters such as the number of laser guide stars, sodium layer depth, wavefront sensor pixel scale, actuator pitch and natural guide star availability. We provide potential areas where costs savings can be made, and investigate trade-offs between performance and cost, and provide solutions that would enable such an instrument to be built with currently available technology. Our key recommendations include a trade-off for laser guide star wavefront sensor pixel scale of about 0.7 arcseconds per pixel, and a field of view of at least 7 arcseconds, that EMCCD technology should be used for natural guide star wavefront sensors even if reduced frame rate is necessary, and that sky coverage can be improved by a slight reduction in natural guide star sub-aperture count without significantly affecting tomographic performance. We find that adaptive optics correction can be maintained across a wide field of view, up to 7 arcminutes in diameter. We also recommend the use of at least 4 laser guide stars, and include ground-layer and multi-object adaptive optics performance estimates.

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arXiv2015

Monte-Carlo modelling of multi-conjugate adaptive optics performance on the European Extremely Large Telescope

The performance of a wide-field adaptive optics system depends on input design parameters. Here we investigate the performance of a multi-conjugate adaptive optics system design for the European Extremely Large Telescope, using an end-to-end Monte-Carlo adaptive optics simulation tool, DASP. We consider parameters such as the number of laser guide stars, sodium layer depth, wavefront sensor pixel scale, number of deformable mirrors, mirror conjugation and actuator pitch. We provide potential areas where costs savings can be made, and investigate trade-offs between performance and cost. We conclude that a 6 laser guide star system using 3 DMs seems to be a sweet spot for performance and cost compromise.

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arXiv2015

Analysis of EMCCD and sCMOS readout noise models for Shack-Hartmann wavefront sensor accuracy

In recent years, detectors with sub-electron readout noise have been used very effectively in astronomical adaptive optics systems. Here, we compare readout noise models for the two key faint flux level detector technologies that are commonly used: EMCCD and scientific CMOS (sCMOS) detectors. We find that in almost all situations, EMCCD technology is advantageous, and that the commonly used simplified model for EMCCD readout is appropriate. We also find that the commonly used simple models for sCMOS readout noise are optimistic, and recommend that a proper treatment of the sCMOS rms readout noise probability distribution should be considered during instrument performance modelling and development.

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arXiv2015

Investigation of Power8 processors for astronomical adaptive optics real-time control

The forthcoming Extremely Large Telescopes all require adaptive optics systems for their successful operation. The real-time control for these systems becomes computationally challenging, in part limited by the memory bandwidths required for wavefront reconstruction. We investigate new POWER8 processor technologies applied to the problem of real-time control for adaptive optics. These processors have a large memory bandwidth, and we show that they are suitable for operation of first-light ELT instrumentation, and propose some potential real-time control system designs. A CPU-based real-time control system significantly reduces complexity, improves maintainability, and leads to increased longevity for the real-time control system.

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arXiv2015

Sensitivity improvements for Shack-Hartmann wavefront sensors using total variation minimisation

We investigate the improvements in Shack-Hartmann wavefront sensor image processing that can be realised using total variation minimisation techniques to remove noise from these images. We perform Monte-Carlo simulation to demonstrate that at certain signal-to-noise levels, sensitivity improvements of up to one astronomical magnitude can be realised. We also present on-sky measurements taken with the CANARY adaptive optics system that demonstrate an improvement in performance when this technique is employed, and show that this algorithm can be implemented in a real-time control system. We conclude that total variation minimisation can lead to improvements in sensitivity of up to one astronomical magnitude when used with adaptive optics systems.

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arXiv2014

Wide-field adaptive optics performance in cosmological deep fields for multi-object spectroscopy with the European Extremely Large Telescope

A multi-object spectrograph on the forthcoming European Extremely Large Telescope will be required to operate with good sky coverage. Many of the interesting deep cosmological fields were deliberately chosen to be free of bright foreground stars, and therefore are potentially challenging for adaptive optics (AO) systems. Here we investigate multi-object AO performance using sub-fields chosen at random from within the Great Observatories Origins Deep Survey (GOODS)-S field, which is the worst case scenario for five deep fields used extensively in studies of high-redshift galaxies. Our AO system model is based on that of the proposed MOSAIC instrument but our findings are equally applicable to plans for multi-object spectroscopy on any of the planned Extremely Large Telescopes. Potential guide stars within these sub-fields are identified and used for simulations of AO correction. We achieve ensquared energies within 75~mas of between 25-35\% depending on the sub-field, which is sufficient to probe sub-kpc scales in high-redshift galaxies. We also investigate the effect of detector readout noise on AO system performance, and consider cases where natural guide stars are used for both high-order and tip-tilt-only AO correction. We also consider how performance scales with ensquared energy box size. In summary, the expected AO performance is sufficient for a MOSAIC-like instrument, even within deep fields characterised by a lack of bright foreground stars.

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arXiv2014

Analysis of on-sky MOAO performance of CANARY using natural guide stars

The first on-sky results obtained by CANARY, the Multi-Object Adaptive Optics (MOAO) demonstrator, are analysed. The data were recorded at the William Herschel Telescope, at the end of September 2010. We describe the command and calibrations algorithms used during the run and present the observing conditions. The processed data are MOAO-loop engaged or disengaged slope buffers, comprising the synchronised measurements of the four Natural Guide Stars (NGS) wavefront sensors running in parallel, and near Infra-Red (IR) images. We describe the method we use to establish the error budget of CANARY. We are able to evaluate the to- mographic and the open loop errors, having median values around 216 nm and 110 nm respectively. In addition, we identify an unexpected residual quasi-static field aberration term of mean value 110 nm. We present the detailed error budget analysed for three sets of data for three different asterisms. We compare the experimental budgets with the numerically simulated ones and demonstrate a good agreement. We find also a good agreement between the computed error budget from the slope buffers and the measured Strehl ratio on the IR images, ranging between 10% and 20% at 1 530 nm. These results make us confident in our ability to establish the error budget of future MOAO instruments.

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arXiv2014

Visible near-diffraction limited lucky imaging with full-sky laser assisted adaptive optics

Both lucky imaging techniques and adaptive optics require natural guide stars, limiting sky coverage, even when laser guide stars are used. Lucky imaging techniques become less successful on larger telescopes unless adaptive optics is used, as the fraction of images obtained with well behaved turbulence across the whole telescope pupil becomes vanishingly small. Here, we introduce a technique combining lucky imaging techniques with tomographic laser guide star adaptive optics systems on large telescopes. This technique does not require any natural guide star for the adaptive optics, and hence offers full sky-coverage adaptive optics correction. In addition, we introduce a new method for lucky image selection based on residual wavefront phase measurements from the adaptive optics wavefront sensors. We perform Monte-Carlo modelling of this technique, and demonstrate I-band Strehl ratios of up to 35% in 0.7~arcsecond mean seeing conditions with 0.5~m deformable mirror pitch and full adaptive optics sky-coverage. We show that this technique is suitable for use with lucky imaging reference stars as faint as Magnitude 18, and fainter if more advanced image selection and centring techniques are used.

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arXiv2014

Faulty actuator tolerance in deformable mirrors for Extremely Large Telescope multi-object adaptive optics

Planned instruments utilising multi-object adaptive optics systems on the forthcoming extremely large telescopes require large numbers of high order deformable mirrors. These devices are a significant cost driver, particularly if specifications regarding the number of faulty actuators are stringent. Here, we investigate the effect on adaptive optics performance that such faulty actuators have, and draw conclusions about how far faulty actuator specifications (and hence cost) can be relaxed without having a significant effect on adaptive optics performance. We also provide performance estimates using a map of faulty actuators from an existing deformable mirror. We investigate the effect of faulty actuators using an end-to-end Monte Carlo adaptive optics simulation code. We find that for actuators stuck at a fixed height above the deformable mirror surface, between $1--2\%$ of actuators can be faulty before significant performance degradation occurs. For actuators that a coupled to nearest neighbours, up to about $5\%$, can be faulty before \ao performance begins to be affected.

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