Atom concentration of a matter wave beam from by the Munich atom laser. The false color 3-D picture has been produced from an image of the shadow cast by the rubidium atoms. It shows a region of 1.2 x 1.2 mm. The continuous beam (blue ridge) escapes from a Bose-Einstein condensate (tall peak in the packground). A continuous output coupler is put into action with a weak radiofrequency field that allows atoms to escape from the magnetic trap by flipping their spin. The atoms are accelerated downward by gravity, forming a matter wave beam of unsprecedented brightness. Full size image available through contact |
Such unprecedented control over atomic motion becomes possible by the laws of quantum mechanics at very low temperatures, close to absolute zero, where the atoms reveal their wave nature.
Atom lasers open new prospects in many areas of science and technology. For instance, it should become possible to accurately deposit atoms on surfaces and thus to produce tiny nanostructures, as needed in future computer circuits. Atom lasers may also lead to extremely precise atomic clocks for future navigation and communication systems.
In their experiments, Tilman Esslinger, Immanuel Bloch and Theodor W. Hänsch have taken pictures of the shadow cast by their atom laser beam. The pencil-like beam contains about half a million rubidium atoms and is accelerated downwards by gravity.
Just as a beam of light, an atom laser beam can be focused and reflected by using lenses or mirrors consisting of laser light (or of magnets). It appears feasible to focus an atom laser beam to a spot size of one nanometer, which is a thousand times smaller than the smallest focus of a laser beam.
The atom laser is based on Bose- Einstein condensation. If a gas is cooled to a few millionth of a degree above absolute zero, the atoms lose their identity and behave as a single entity, some kind of "super atom". Such a Bose-Einstein condensate was first produced by American scientists in 1995.
In the Munich experiment, a dilute gas of rubidium atoms is captured in a sophisticated low-power magnetic trap and cooled down to reach Bose-Einstein condensation. With the help of a radiofrequency field the scientists flip the atomic spin so that atoms are allowed escape from the magnetic trap. In vacuum, the atoms are accelerated by gravity and form a parallel beam of coherent matter waves.
It the radiofrequency field is turned on before condensation sets in, the atom laser can only reach threshold, if there is laser "gain". Unlike a Bose-Einstein condensate, such a laser relies on matter wave amplification by stimulated elastic scattering of rubidium atoms just as an optical laser relies on light amplification by stimulated emission of radiation.
Two years ago, a group at MIT demonstrated the first pulsed atom laser. The Munich group is the first to produce a continuous matter wave beam which can be maintained for a tenth of a second. The wave packet of each atom extends over the entire length of this beam, so that a quantum object of truly macroscopic dimensions is created. The high brightness and coherence of such a matter wave beam opens exciting perspectives for the young fields of atom optics and atom interferometry.
Journal
Physical Review Letters