Optical Ferris Wheel

A new form of optical lattice, a ring-shaped lattice which spins about, has been planned by physicists at the University of Glasgow and the University of Strathclyde. In an optical lattice a web of laser beams can hold a collection of atoms in place in free space. If the frequencies of the two holographically generated laser beams are different, the resultant lattice can be spun about.

In fact the laser pattern is created in this case through the use of a hologram. The trapped atoms can reside in either discrete lozenge-shaped parcels (in some cases positioned in the dark regions that result from the interference of laser beams) or spread out over a continuous ring shape (see movie at http://www.physics.gla.ac.uk/Optics/projects/AM/).

One goal of pinioning atoms in a light-free dark zone is to reduce unwanted warming of the atoms, which need to be ultracold in order to carry out fundamental tests of interatomic forces. Furthermore, as theorists are very interested in studying atoms lodged in infinitely long one-dimensional strings, and since such strings are difficult to create experimentally, the next best thing is bend the string around on itself in the shape of a ring; hence the motivation for producing a ring optical lattice.

The Scottish haven’t yet installed atoms into their ring but according to Sonja Franke-Arnold (s.franke-arnold@physics.gla.ac.uk), she and her colleagues at Strathclyde plan soon to inject a Bose-Einstein condensate (BEC) of rubidium atoms. (Franke-Arnold et al., Optics Express, 9 July 2007; the journal is public access and the text can be obtained at http://www.opticsexpress.org/abstract.cfm?id=138976)