Modelling and Exploiting the Hyperfine Structure of Alkali Atoms for Generation of Nonclassical Light and Rydberg-Atom-Based Field Sensing

Alkali atoms are a workhorse in quantum optics, owing to the relative simplicity of their elec- tronic structure, which affords remarkable and reliable control over their behaviour. In particular, the ability to probe and manipulate alkali atoms with electromagnetic fields provides an important resource for studying and harnessing their fundamental properties. This thesis explores interac- tions between alkali atoms and light, to uncover ways of exploiting their properties for a variety of purposes. The main results of the thesis are divided into three main parts, as we detail below. Firstly, we develop theoretical models of effective interactions between alkali atoms in cavity quantum electrodynamics (cavity QED) systems, building on previous work in this area. The models are based on Raman transitions between the Zeeman sublevels of hyperfine ground states in an alkali atom. We show that by coupling light to both D-lines of the atom simultaneously, a versatile effective Hamiltonian can be realised with terms that can be manipulated independently. Additionally, we show that, with careful arrangement of the fields, the effective interactions can persistinsteadystate, continuouslyoutputtinglightthatcarriessignaturesoftheinteraction. These models reveal novel mechanisms for generating nonclassical states of light, with the potential for producing Wigner-negative and quadrature-squeezed light from single-atom sources. We simulate full hyperfine structure models of the interactions, using parameters inspired by modern cavity QED architectures, to demonstrate the robustness of their implementation in a real atom. Secondly, we explore nonclassical photon statistics through specific configurations of single- atom nanofibre cavity QED systems. By coupling an alkali atom to nanofibre cavity modes, we demonstrate antibunching and strong two-mode correlations, showcasing the versatility of these systems for generating nonclassical photon statistics. We consider two schemes for their photon correlations, each based on coupling two cavity modes to a single atom. First, the generation of nonclassical light at telecom-band wavelengths is studied, using cascaded transitions within a caesium atom. The atomic states are chosen such that one of the cavity modes is resonant at a telecom-band frequency. Second, we explore the coupling an adjacent pair of resonances of a long cavity to a strongly-driven atom. The characteristic emission spectrum is matched to the free spectral range of the cavity. In both cases, we consider simplified models to understand the critical behaviour of the systems, and then use full hyperfine structure models to examine the viability of implementing them in modern nanofibre cavity QED systems. Finally, we present a model for the interaction of light with a thermal cloud of Rydberg atoms. The random thermal motion of a room-temperature gas necessitates ensemble averaging in order to predict the absorption spectrum for a probe beam. The effective model that we develop accurately predicts the absorption profile of electromagnetically-induced transparency in the atomic cloud, offering insights for experiments in atom-based sensing of microwave-frequency electromagnetic fields. Overall, this thesis enhances the fundamental understanding of alkali atom-light interactions and adds to the ever-growing quantum-optical toolbox.

Name thesis:degree_name

PhD

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Physics

Grantor dc:publisher

ResearchSpace@Auckland

Year dc:date.issued

2025

Author dc:creator

• Elliott, Alexander

Advisors dc:contributor.advisor

• Parkins, Scott
• Blakie, Blair

Statement dc:rights

• Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated.

Licence dc:rights.uri

• https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm

Handle dc:identifier.uri

https://hdl.handle.net/2292/75705

OAI identifier oai:identifier

oai:researchspace.auckland.ac.nz:2292/75705