Trapping and Cooling of Bosonic Strontium for a Long-Baseline Atomic Interferometer Observatory and Network (AION)
The Atom Interferometry Observatory and Network (AION), a consortium of UK institutes, is developing a long-baseline atom interferometer to search for fundamental physics beyond the standard model, such as decihertz gravitational waves, scalar and vector-ultralight dark matter, fifth-force, and macroscopic tests of quantum mechanics. Dark matter and gravitational waves hold the key to unlocking the intricacies of the universe. For example, dark matter explains why galaxies retain their structural integrity despite high rotational velocities, while gravitational waves offer fresh insights into early universe conditions close to the big bang. However, specific subsets such as decihertz gravitational waves and ultra-light dark matter remain hard to detect with current instruments. Atom interferometers can be sensitive in the decihertz range, bridging the frequency gap for gravitational waves and filtering potential dark matter models. In an atom interferometer, atomic wavefunctions are split and recombined, generating interference patterns based on the differences in phase accumulated along both arms. The AION apparatus consists of a series of vertically separated atom interferometers. Gravitational waves stretch and compress space-time along the baseline, while ultra-light dark matter induces oscillations in the atomic transition frequency − both leading to time-varying signals in the readout. Differential measurements can then be performed to extract phase differences and deduce potential findings. This thesis presents the development of a first-generation cold strontium atom source tailored to AION. I report on the experimental results of the technologies to efficiently cool and trap bosonic strontium in the Cambridge AION-1 tabletop demonstrator. The technologies described in this thesis ensure straightforward integration into subsequent iterations of the long-baseline AION system. I describe the apparatus in detail, highlighting the relevant infrastructure and experimental setup implemented to cool and trap bosonic strontium atoms. The apparatus employs a three-chamber configuration, where a high-temperature oven and a two-dimensional 461 nm magneto-optical trap (MOT) delivers a continuous source of strontium atoms into a three-dimensional 461 nm MOT for initial cooling and trapping. A Pound-Drever-Hall stabilised Ti:Sapphire laser, narrowed to sub-kilohertz linewidth at 689 nm, facilitates further cooling in a three-dimensional 689 nm MOT addressing the narrow inter-combination line. Broadband to narrowband sequences enable the experimental realisation of a cold strontium atom cloud with temperatures of a few micro-kelvins, suitable for optical dipole trapping and transport.
AION, Atom Interferometry, Dark Matter, Fundamental Physics, Gravitational Waves, Strontium, Ultracold Atom
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