Magnetic Atom Optics

Abstract

Over the last decade, the explosion of techniques for cooling, trapping, and manipulating atoms [1] has given birth to the field of atom optics [2] in which atoms are reflected, refracted, and diffracted, much as photons are in ordinary optics. Until recently the manipulation of atoms in flight has been largely restricted to small angle deflections of atomic or molecular beams. Focusing is typically achieved by electric quadrupole or magnetic hexapole fields whose gradients provide a force proportional to the distance from the axis [3, 4]. In two special cases atomic beams have also been focused by quantum reflection from a mirror: H from liquid He [5] and He from silicon [6]. With the advent of laser cooling it is now possible to prepare extremely cold atomic clouds which have such low thermal velocity that they fall almost vertically under gravity and can readily be deflected through large angles. In this paper we describe how we have imaged an 18 μK cloud of ⁸⁵Rb atoms bouncing freely on a horizontal, concave magnetic atom mirror (radius of curvature R). A high-quality image is observed even after 14 reflections. Initially compact, the cloud is alternately collimated (odd bounces) and brought back to a focus (even bounces) when dropped from a height R/4. This multiple reconstruction of a thermally expanding cloud hinges on the microscopic reversal of the atomic motion. We discuss the principle of the magnetic reflector, the factors limiting the resolution of the mirror and the method of construction. We also speculate on some of the future applications of this method of atom manipulation