Calorimetry of an ultracold Bose gas and cavity quantum electrodynamics with an optical nanofibre

Abstract

In this Thesis we present experiments involving laser cooled alkali atoms. We perform calorimetry experiments with a harmonically trapped Bose gas of 87Rb atoms. Starting from a Bose-Einstein condensate confined in an optical trap, we transfer a precise and known amount of energy to the system using one of two independent methods. Following a rethermalisation period within the trapping potential, we measure the resulting temperature of the atoms through absorption imaging. Comparisons of experimental data to various theoretical models show that the thermodynamic behaviour of the system is well described by a Hartree-Fock model for an interacting gas. In a separate experiment we have utilised a nanofibre, a section of optical fibre that has been tapered to a subwavelength diameter waist, as a tool for interfacing 133Cs atoms with the guided optical mode of the fibre through an evanescent field. The tight transverse confinement of the guided mode allows for efficient light–matter interactions at the few photon level. We enhance these interactions by forming an all-fibre ring geometry cavity containing a nanofibre section, and perform cavity quantum electrodynamics experiments with an ensemble of laser cooled caesium atoms. Due to a collective enhancement of the coupling rate by the ensemble of atoms, we observe well-resolved vacuum Rabi splitting of the cavity transmission in the weak driving limit. Additionally, we investigate the power dependence of the atom–cavity transmission on resonance, and observe saturation of the atoms at higher driving strengths. We also present a simple theoretical model to describe the behaviour of this system. Finally, modern cold atom experiments demand a high degree of control and reproducibility, which can be best provided through computer control. We present our implementation of a computer interface for the experiment, as well as various custom built hardware interfaces which are integrated into our control scheme. Our system allows for scripting of an experimental sequence, adjustment of experimental settings, and the ability to collect and analyse experimental data from a central computer.