A compact cold-atom microwave clock prototype

Thesis

The transfer of quantum technologies from research laboratories into practical, compact devices brings with it the promise of enhancing a variety of real-world applications. This thesis details the design, construction, and characterisation of a compact cold-atom microwave clock prototype. The prototype consists of laser, control electronics, and physics package subsystems. As part of the physics package, a new design for a microwave cavity is discussed, which should lend itself well to a compact atomic clock. The prototype is intended as a benchtop experiment, where the procedure of interrogating a cloud of caesium atoms during free fall can be explored. Both open- and closed-loop spectroscopy of the clock transition have been performed. The linewidth of the observed Rabi spectrum, which is limited by a short pulse length chosen for diagnostic purposes, is 159(1) Hz. The corresponding short-term fractional frequency stability was measured to be 1.9 × 10⁻⁹ τ^−1/2 out to 1000 s, which is still limited by experimental systematics rather than a fundamental limit of the atomic clock architecture. Through further optimisation and implementation of a Ramsey interrogation sequence with a longer drop time, this frequency stability can be improved to the level of low parts in 10⁻¹² τ^−1/2. Such a clock would be highly suited to applications such as GNSS holdover and radio astronomy. The prototype developed here is a significant step towards the next generation of compact microwave clocks that rely on cold atoms at temperatures of tens of microkelvin rather than thermal atoms.

Authors: Knapp, M

• DOI: 10.5287/ora-eoz0xb4oo
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: compact atomic clock; laser cooling; cold atoms; atomic clock; microwave clock
• Subjects: Laser cooling; Atomic clocks