Atoms Trapped by the Light

Stig Stenholm

We consider the mechanical forces exerted on atoms by light as a tool to make the atom more concrete as a particle. It can be pushed, trapped and observed in its own scattered light. Recent theoretical and experimental progress in the field of cooling and trapping of atoms demonstrates their palpable reality. The theory of the mechanical manifestations of light is reviewed, and its application to laser cooling is discussed. Traps for atoms are considered. The feasibility of pure light traps is discussed, and the use of other types of traps in laser applications is reviewed. We present briefly the main experiments proving the possibility of laser cooling and trapping. A brief discussion of applications and future experimental possibilities is given.

John Maddox

Glen D. Gillen, Katharina Gillen, Shekhar Guha

In this chapter we present an interesting application of the propagation of laser light through linear optical media: the ability to spatially confine (trap) cold atoms within localized light intensity patterns. We first present some of the fundamentals for understanding how light can trap an atom. Depending upon the relationship between the properties of the atom and the properties of the laser light, atoms can be trapped in either localized dark spots, or localized bright spots. We will describe several light patterns for trapping atoms: The tightly localized bright and dark regions in the near-field diffraction patterns presented in Chapters 7 and 8 , The near-field patterns projected to a location far away from the diffracting aperture, and Polarization-dependent movable light field traps based on the near-field diffraction patterns.

Andreas Osterwalder

E. Vetsch

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.

Pierre Meystre