Alder, Fiona Alexandra; (2025) Novel quantum sensors for directional dark matter detection. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Directional detection of dark matter remains a crucial challenge in experimental physics, requiring novel approaches to explore the wide range of potential candidates, and to overcome limitations in traditional detection techniques. This thesis presents the development and analysis of a levitated optomechanical system designed to detect weak, rare interactions consistent with dark matter particle scattering. Utilising optically trapped nanospheres in ultra-high vacuum, this work investigates the feasibility of measuring momentum transfers from candidate dark matter interactions with high precision. The experiment aims to detect composite self-interacting dark matter by measuring induced recoils in a levitated particle. To achieve this, the experimental setup was designed and optimised so as to minimise background noise and ensure precise calibration. A novel calibration approach was developed using laser interference fringes as a standard ruler to characterise the particle’s motion, ensuring accurate recoil measurements. A robust data analysis framework was implemented, employing optimal filtering techniques (Wiener Kolmogorov filtering) to extract potential dark matter signals from background noise. A key tool of this work was the modelling of gas molecule collisions with the levitated sphere to quantify background forces and noise sources. By simulating diffuse reflection and temperature-dependent interactions, a framework was established for resolving momentum transfers in Cartesian coordinates and distinguishing potential dark matter-induced signals from thermal and stochastic effects. Simulated dark matter-like events were experimentally introduced to validate detection and reconstruction methods. Initial results from the first science run were analysed, assessing the detector’s sensitivity and identifying event types that inform future optimisations. The research presented establishes levitated optomechanical systems as promising platforms for rare-event searches, contributing to the advancement of directional dark matter detection and laying the groundwork for future constraints on composite dark matter models.

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