Multicolor Atom Laser.

A new theoretical study suggests that intense atom lasers would not be mono-chromatic. In ordinary optical lasers the coordinated build-up of a coherent light pulse ensures that all light waves possess a single energy; in other words, all the laser light would have a single color. By analogy, the action of an atom laser, consisting of the release of gaseous atoms (in the form of waves) from the magnetic-field constraints used to create a Bose Einstein condensate (BEC), should be monochromatic. After all, the atoms in a BEC have been chilled to such an extreme extent that all the atoms possess the same energy.

Stephen Choi and his colleagues at the University of Massachusetts Boston maintain that in dilute BECs this is indeed the case. But in dense BECs, frequent collisions among atoms will promote classes of atoms to higher energies as well. In effect, the inter-atomic interactions "generate" atom waves at alternative, harmonic energies. The UMB researchers next show how this harmonic generation can be demonstrated. They do this by simulating what happens when a BEC is sent through an interferometer, a device in which a coherent train of waves is divided into two components, steered along different paths, and then recombined to create a characteristic interference pattern.

In this simulated interferometer the BEC atoms don't move through space. Instead the dividing, steering, and recombining are carried out by subtly modulating the magnetic fields used to confine the BEC in the first place. The presence of extra "harmonic" atom waves will make the resultant interferometer pattern more complicated. But this, Choi (stephen.choi@umb.edu) says, is not all bad. It can, for example, lead to greater sensitivity when the atom interferometer is put to use in certain devices, such as gyroscopes. (Choi et al., Physical Review A, April 2008)