Guided Atom Laser

A cloud of atoms distilled into the form of a Bose Einstein condensate (BEC) acts likes a single coherent thing. Furthermore, the BEC acts like a wave. It can and has been extracted from the trap structure in which the condensate was made and allowed to propagate just like a laser beam, except that the waves in this case consist not of electromagnetic radiation but atoms. In previous atom lasers the atoms, subject to the force of gravity, accelerated; this has the effect of decreasing the wavelength of the atom waves.

Now, for the first time, physicists of Alain Aspect's atom optics group (www.atomoptic.fr) from the Institut d'Optique Graduate School, Palaiseau (south of Paris), have been able to extract atoms from a BEC trap on a quasicontinuous basis while simultaneously sending them down a horizontal optical guide with an unprecedented level of control over direction, intensity, and wavelength, the latter being kept constant during the propagation.

William Guerin (william.guerin@institutoptique.fr), a researcher on the team led by Vincent Josse and Philippe Bouyer, says that the advantage of this quasicontinuous guided atom laser beam over the previously realized pulsed guided beams (when the BEC is extracted all at once) is its much narrower velocity spread. In the Palaiseau atom laser, the atoms are extracted by converting some of them from a magnetic state to a nonmagnetic state. After this, the confining magnetic fields of the trap no longer influence the atoms and the atom waves emerge with a typical velocity of 10 mm/sec and a velocity spread of a few microns/sec, a factor of 1000 sharper than for pulsed laser operation (see figure at http://www.aip.org/png/2006/273.htm).

The atom laser in the Paris device is driven forward by a beam of light in a very directional and efficient process; no atoms are lost during extraction or transport across a 1 mm guide. This new atom laser opens promising prospects for applications in atom interferometry or more fundamental studies of matter wave propagation. (Guerin et al., Physical Review Letters, 17 November 2006