The controlled emission and absorption of single photons is an important enabling technology in the fields of quantum communication, cryptography and computing. We have realised a novel single photon source, based on a miniature ‘endcap' ion trap with integrated optical fibres. To minimise distortion of the trapping field the fibres are tightly integrated and recessed within the two hollow cylindrical rf electrodes of the trap. This allows us to bring the fibres to within approximately 300 μm of the trapped ion. With the fibres in place we are able to collect the ion's fluorescence using no further optics. In this thesis the ion trap is fully characterised, and the quantum nature of the light demonstrated in the results of a variant on the Hanbury Brown-Twiss photon-correlation experiment. The scheme will ultimately be extended to implement a coherent ion-photon interface through strong coupling cavity-QED. Towards this end, an ultra-high-finesse cavity has been designed and fabricated by laser-machining and coating surfaces with a range of radii of curvature on the end facets of the fibres. To improve the stability and precision manipulation of the cavity in-vacuum, an entirely new trap has been designed and built. Finally, the current status of the fibre cavity and the outlook for the experiment are presented.

The combination of an ion trap with a high finesse optical cavity is an ideal system for the investigation of strong coupling cavity quantum electrodynamics, and allows the observation of a number of interesting quantum phenomena. To achieve the small mode volumes required without impairing the ion trapping small traps with a short ion electrode distance are needed. Two microscopic linear rf ion traps have been developed and built to accommodate experimental cavities of lengths of several 100 microns. The first trap design, the 'sandwich' trap, was successfully used to trap 40Ca+ - ions for several hours. It was characterised extensively including a measurement of the heating rates of the ions in the trap. Spectroscopy measurements of the cooling transition, as well as the two repumping transitions were carried out. The second trap design, the 'alumina' trap, also successfully trapped 40Ca+ - ions, and a full characterisation of this trap was made. The experimental cavity was installed at a preliminary cavity length distance of 3.7 mm. The cavity characteristics were examined. Finally the trapped ions were overlapped with the cavity mode by adjusting the trap minimum position along the trap axis via dc voltages and the vertical position of the cavity. To progress further a locking scheme for the cavity length as well as a single - photon detection setup are necessary. To achieve strong coupling a reduction of the cavity length will have to be made.

Gravitational lensing of photons in the Cosmic Microwave Background (CMB) can be described by an integrated potential along the line of sight, the CMB lensing potential. Covariances in maps of the CMB are generated by the lensing effect, and are used to reconstruct the lensing potential itself, which is a useful probe of the matter distribution. The CMB lensing potential has been measured to high significance with CMB temperature data. However, signal to noise for lensing reconstruction from CMB polarization data is expected to be much better due to the presence of the lensing B-mode. Upcoming data from ground based CMB polarization instruments will provide high resolution maps over small patches of the sky. This will provide much better lensing reconstruction, but also presents data analysis challenges. This thesis begins with an introduction to the field of CMB lensing and CMB lensing reconstruction. The second chapter details the biases present in reconstructing the lensing potential from CMB polarization maps considering first the full sky, and then small patches of sky. It also shows that using the pure-B mode formalism for the CMB polarization leads to improved lensing reconstruction over the naive case on the cut sky. Given the upcoming improvement in the CMB lensing reconstruction, it is expected that cross-correlations of the CMB lensing with other structure tracers, such as galaxies, will yield improved information for cosmology. It is also expected that the CMB lensing will become useful to help constrain uncertainties in the galaxy power spectrum, and provide information on the linear galaxy bias and redshift distribution. The third chapter of the thesis forecasts the power of cross correlation science for a number of galactic and non-galactic parameters. Finally, the CMB lensing effects the level of non-Gaussianity observed in the CMB. The fourth chapter of the thesis is a study of the lensing effect on the primordial squeezed bispectrum. We conclude in the fifth chapter.