A Versatile Atom Transport Apparatus for Photonics

Abstract

This thesis describes and characterizes a setup to conduct experiments combining the fields of cold atoms and nanophotonics. Furthermore, a series of numerical simulations is employed to deepen of atom transport under experimentally realistic conditions. The study of cold atoms is usually fundamental in nature and a very clean approach to investigate the laws of physics. High purity samples of atoms are cooled down to millikelvins or microkelvins. The potential landscape for the atoms can be carefully controlled using lasers and/or magnetic fields. Since the atoms' responses to electric, magnetic or electromagnetic fields are known with very high fidelity, any deviations to the state the atoms are prepared in can be precisely measured. Nanophotonics is the study of light close to or beyond the diffraction limit. In this region the field-like nature of light starts to play a role. By confining light in sub-wavelength-sized structures, high peak intensities can be achieved, giving rise to exciting non-linear optics phenomena. The strong field gradient that can be created allows, for instance, precise spectroscopy measurements, phase-sensitive sub-wavelength microscopy, as well as producing highly receptive sensing devices. Combining cold atoms and nanophotonics creates strong synergy effects. It gives access to strong coupling of light and matter. The scalability of nanophotonics now extends to atomic physics. Atoms can be trapped, coupled and manipulated at very small length scales, and in large numbers. Moreover, the potential landscape for atoms is highly customizable. The rubidium isotope 87 is used in this setup. A cloud of rubidium atoms is gathered and cooled in a two dimensional magneto-optical trap (MOT). Since the atoms are only cooled in two dimensions, they are free to escape in the third dimension and load a following three dimensional MOT. The atoms are now cooled further, compressed and loaded into an optical dipole trap. This dipole trap transports the atoms close to a sample inside the vacuum chamber. A moving optical lattice, or optical conveyor belt, brings the atoms then close to the sample surface. Now experiments can be conducted, studying the interaction of cold atoms and strongly confined light. The atom transport down to the sample surface shows some unexpected behaviour: the atoms seem to spread through the optical lattice during transport. A combination of microscopic and macroscopic numerical simulations, including genetic algorithms, are used to deepen our understanding of the underlying physics. This also allows us to get access to experimental variables that cannot be directly obtained.