Trapping and manipulating ultracold atoms and degenerate quantum gases in magnetic micropotentials is reviewed. Starting with a comprehensive description of the basic concepts and fabrication techniques of microtraps together with early pioneering experiments, emphasis is placed on current experiments on degenerate quantum gases. This includes the loading of quantum gases in microtraps, coherent manipulation, and transport of condensates together with recently reported experiments on matter-wave interferometry on a chip. Theoretical approaches for describing atoms in waveguides and beam splitters are briefly summarized, and, finally, the interaction between atoms and the surface of microtraps is covered in some detail.

Magnetic microtraps for ultracold atoms

Bose-Einstein condensation of cesium atoms is achieved by evaporative cooling using optical trapping techniques. The ability to tune the interactions between the ultracold atoms by an external magnetic field is crucial to obtain the condensate and offers intriguing features for potential applications. We explore various regimes of condensate self-interaction (attractive, repulsive, and null interaction strength) and demonstrate properties of imploding, exploding, and non-interacting quantum matter.

https://science.sciencemag.org/content/sci/299/5604/232.full.pdf

Bose-Einstein Condensation of Cesium

We report on the creation of a two-dimensional Bose-Einstein condensate of cesium atoms in a gravito-optical surface trap. The condensate is produced a few microm above a dielectric surface on an evanescent-wave atom mirror. After evaporative cooling by all-optical means, expansion measurements for the tightly confined vertical motion show energies well below the vibrational energy quantum. The presence of a condensate is observed in two independent ways by a magnetically induced collapse at negative scattering length and by measurements of the horizontal expansion.

/pdf/two-dimensional-bose-einstein-condensate-in-an-optical-2orpzhipn3.pdf

Two-Dimensional Bose-Einstein Condensate in an Optical Surface Trap

Dispersion forces in macroscopic quantum electrodynamics

This chapter discusses the applications of generation of dark hollow beams. A light beam with a ring-shaped intensity distribution is a “dark hollow beam (DHB)”. Such light beams possess both spin and orbital angular momentum and are described in terms of superposition of Laguerre-Gaussian beam (LGB) modes. DHBs are characterized by some practical parameters, such as the dark spot size (DSS), the beam width ( W DHB ), the beam radius ( r 0 ), the ringbeam width ( W r ), and the width-radius ratio (WRR). The chapter characterizes the DHBs and their physical parameters. The chapter describes various experimental schemes for DHB generation. The chapter reviews the methods and basic principles for generating DHBs and discusses the classifications of DHBs and their areas of applicability. The chapter reviews the applications of DHBs in modem optics, atom optics, and coherent matter-wave optics. The chapter also explains the current stage of DHB research and presents a perspective outlook for future studies and applications of DHBs.

Chapter 3 Generation of dark hollow beams and their applications

A dense gas of cesium atoms at the crossover to two dimensions is prepared in a highly anisotropic surface trap that is realized with two evanescent light waves. Temperatures as low as 100 nK are reached with 20,000 atoms at a phase-space density close to 0.1. The lowest quantum state in the tightly confined direction is populated by more than 60%. The system provides atoms at a mean distance from the surface as low as 1 microm, and offers intriguing prospects for future experiments on degenerate quantum gases in two dimensions.

Evanescent-wave trapping and evaporative cooling of an atomic gas at the crossover to two dimensions.

Institut fu¨r Experimentalphysik, Universit¨at Innsbruck, Technikerstr. 25, A-6020 Innsbruck, Austria(Dated: August 16, 2002)A dense gas of cesium atoms at the crossover to two-dimensionality is prepared in a highlyanisotropic surface trap that is realized with two evanescent light waves. Temperatures as low as100nK are reached with 20.000 atoms at a phase-space density close to 0.1. The lowest quantumstate in the tightly conﬁned direction is populated by more than 60%. The system oﬀers intriguingprospects for future experiments on degenerate quantum gases in two dimensions.

Evanescent-wave trapping and evaporative cooling of an atomic gas near two-dimensionality

We report on cooling of an atomic caesium gas closely above an evanescent-wave atom mirror. At high densities, optical cooling based on inelastic reflections is found to be limited by a density-dependent excess temperature and trap loss due to ultracold collisions involving repulsive molecular states. Nevertheless, very good starting conditions for subsequent evaporative cooling are obtained. Our first evaporation experiments show a temperature reduction from 10 μK down to 300 nK along with a gain in phase-space density of almost two orders of magnitude.

Optical and evaporative cooling of caesium atoms in the gravito-optical surface trap

An optical microtrap is realized on a dielectric surface by crossing a tightly focused laser beam with a horizontal evanescent-wave atom mirror. The nondissipative trap is loaded with $\ensuremath{\sim}{10}^{5}$ cesium atoms through elastic collisions from a cold reservoir provided by a large-volume optical surface trap. With an observed 300-fold local increase of the atomic number density approaching ${10}^{14}{\mathrm{cm}}^{\ensuremath{-}3},$ unprecedented conditions of cold atoms close to a surface are realized.

Cold-atom gas at very high densities in an optical surface microtrap

We report on cooling of an atomic cesium gas closely above an evanescent-wave atom mirror. At high densitities, optical cooling based on inelastic reflections is found to be limited by a density-dependent excess temperature and trap loss due to ultracold collisions involving repulsive molecular states. Nevertheless, very good starting conditions for subsequent evaporative cooling are obtained. Our first evaporation experiments show a temperature reduction from 10muK down to 300nK along with a gain in phase-space density of almost two orders of magnitude.

M. Hammes

Papers

Evanescent-wave trapping and evaporative cooling of an atomic gas at the crossover to two dimensions.

Evanescent-wave trapping and evaporative cooling of an atomic gas near two-dimensionality

Optical and evaporative cooling of caesium atoms in the gravito-optical surface trap

Cold-atom gas at very high densities in an optical surface microtrap

Optical and evaporative cooling of cesium atoms in the gravito-optical surface trap