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Bulletin of the Korean Chemical Society

Optical Lattices for Optimal Atom Lenses

Chang Jae Lee

Published Jan 20, 2017• 0 citations
Publisher

Abstract

Optical lattices have been used for focusing atomic beams to produce arrays of parallel nanowires and nanodots. Atomic dynamics in optical lattice lenses can be treated with either a method analogous to classical ray‐optics or wave mechanics. In this article, we investigate the dynamics by treating atoms quantum mechanically, moving in semiclassical optical lattices. The goal is to provide general conditions for achieving optimal atom focusing. Effects of experimental parameters such as detuning, laser power, and atom–lattice interaction time, and the shape of the optical lattice potentials on atom focusing are studied. Based on these analyses, strategies for achieving optimal atom focusing are provided.

DOI
10.1002/bkcs.11075

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Bulletin of the Korean Chemical Society•May 20, 2003•1 citation
Optical lattices have been used for focusing atomic beams to produce arrays of parallel nanowires and nanodots. Atomic dynamics in optical lattice lenses can be treated with either a method analogous to classical ray‐optics or wave mechanics. In this article, we investigate the dynamics by treating atoms quantum mechanically, moving in semiclassical optical lattices. The goal is to provide general conditions for achieving optimal atom focusing. Effects of experimental parameters such as detuning, laser power, and atom–lattice interaction time, and the shape of the optical lattice potentials on atom focusing are studied. Based on these analyses, strategies for achieving optimal atom focusing are provided.
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The principal element in any sort of optics is a lens. It is essential to create laser field configurations capable of focusing neutral atomic beams. There are two possibilities for focusing an atomic beam by laser light: by using the gradient force or by using the light pressure force. The force effecting the focusing of an atom in a beam should be proportional to the atomic displacement. This criterion must be satisfied for the force to produce the true “image”: if this criteria is not met, the image is blurred, i.e. there are aberrations. An approach to treat the focusing of atomic beam by laser light is to use the path integral technique to calculate the evolution of atomic wave function as it propagates in laser field. A particle-optical approach also can be used for treatment of focusing of atoms by laser light. The quadratic radial dependence of the potential is a necessary condition for focusing of atoms.
This thesis gives an account of work done on semi-classical and quantum Monte Carlo simulations in far-detuned optical lattices. Firstly, the basic principles of laser cooling of atoms are presented including a short introduction to optical lattices in the near and far-detuned regime. A detailed analysis is made of the band-structure of optical lattices, using the Bloch formalism, and of the bound-state population distribution appropriate for a thermal sample of trapped atoms. Secondly, a general overview is given of the quantum Monte Carlo method for simulating the dynamics of atom-light interactions. This is followed by a detailed study of the concept of Raman cooling, which is a useful tool to prepare atoms in the ground motional state of the lattice and an important first step to achieving quantum state control with ultra-cold atoms. A simplified model of Raman cooling is introduced and simulated using the quantum Monte Carlo wave-function approach. Then the implementation of simulations of resolved-sideband Raman cooling based on this model is discussed as is how the results were used to optimize the experimental work done by our group. The results of these simulations show for the first time that the quantum Zeno effect has a crucial impact on the efficiency of Raman cooling experiments. Also the experimental measurements of the temperature of Raman sideband cooled atoms for a range of parameters are compared with theoretical results and shows a good qualitative agreement. Thirdly, the results of semi-classical numerical simulations of parametric excitation in optical lattices are presented. It is shown that the modulation of the potential can result in selective parametric excitation of trapped atoms. The theoretical results show good qualitative agreement with experiment. The thesis is concluded with a description of possible avenues for future studies on quantum state control in optical lattices.
We have simulated the dynamics of interacting atoms in optical lattices. The periodic lattice structure is produced with laser beams detuned a few linewidths to the red from the atomic transition. The atoms localize in lattice sites as a steady state is reached during the cooling, but they can still to some extent move between the sites. Our Monte Carlo Wave Function simulations show that in such situations the interactions can lead to evaporative cooling of the atoms as the hotter ones are ejected from the lattice.
The light pressure force from an optical standing wave (SW) can focus an atomic beam to submicrometer dimensions. To make the best of this technique it is necessary to find a set of optimal experimental parameters. In this paper we consider theoretically the chromium atoms focusing and demonstrate that the focusing performance depends not only on the strength of but also on the time atoms take to traverse the force field. The general conclusions drawn can easily be applied to other atoms. To analyze the problem we numerically integrate a coupled time-dependent Schro¨dingerSchr{\"{o}}dingerSchro¨dinger equation over a wide range of experimental parameters. It is found that an optimal atomic beam speed-laser intensity pair does exist, which could give substantially improved focusing over the one with the experimental parameters given in the literature. It is also shown that the widely used classical particle optics approach can lead to erroneous predictions.