Optical interface based on a nanofiber atom-trap

In this thesis, I present the realization of a fiber-optical interface using optically trapped cesium atoms, which is an efficient tool for coupling light and atoms. The basic principle of the presented scheme relies on the trapping of neutral cesium atoms in a two-color evanescent field surrounding a nanofiber. The strong confinement of the fiber guided light, which also protrudes outside the nanofiber, provides strong confinement of the atoms as well as efficient coupling to near-resonant light propagating through the fiber. In chapter 1, the necessary physical and mathematical background describing the propagation of light in an optical fiber is presented. The exact solution of Maxwell’s equations allows us to model fiber-guided light fields which give rise to the trapping potentials and the atom-light coupling in the close vicinity of a nanofiber. Chapter 2 gives the theoretical background of light-atom interaction. A quantum mechanical model of the light-induced shifts of the relevant atomic levels is reviewed, which allows us to quantify the perturbation of the atomic states due to the presence of the trapping light-fields. The experimental realization of the fiber-based atom trap is the focus of chapter 3. Here, I analyze the properties of the fiber-based trap in terms of the confinement of the atoms and the impact of several heating mechanisms. Furthermore, I demonstrate the transportation of the trapped atoms, as a first step towards a deterministic delivery of individual atoms. In chapter 4, I present the successful interfacing of the trapped atomic ensemble and fiber-guided light. Three different approaches are discussed, i.e., those involving the measurement of either near-resonant scattering in absorption or the emission into the guided mode of the nanofiber. In the analysis of the spectroscopic properties of the trapped ensemble we find good agreement with the prediction of theoretical model discussed in chapter 2. In addition, I introduce a non-destructive scheme for the interrogation of the atoms states, which is sensitive to phase shifts of far-detuned fiber-guided light interacting with the trapped atoms. The inherent birefringence in our system, induced by the atoms, changes the state of polarization of the probe light and can be thus detected via a Stokes vector measurement.