Bright solitons

Bright Solitons in a Bose–Einstein condensate. A soliton is a localized wave that, because of nonlinear effects, can travel for long distances without spreading out or losing its original shape. Solitons can occur in all kinds of waves, including sound and light. In fact, solitons are regularly used in telecommunications in optical fibers. Essentially a macroscopic matter wave, a BEC can also form solitons. Usually, however, a BEC quickly spreads after it is released from the trap in which it was created. Now, groups at Rice University in Houston and at the Ecole Normale Supérieure in Paris have been able to form BEC solitons with lithium-7 atoms. Both groups used a tunable magnetic field to adjust the interatomic interactions from repulsive—necessary to form a stable condensate—to weakly attractive. The attractive interactions provided a self-focusing nonlinearity that exactly compensated for wavepacket dispersion. After releasing the atoms into a 1D potential, both groups observed solitons that propagated without changing shape for more than a millimeter—a truly macroscopic distance. The Rice experimenters formed a train of up to 10 individual solitons, which appeared to repel each other as they oscillated in a weakly harmonic potential. The Paris group set up an open waveguide and accelerated a single soliton. Matter-wave solitons may prove useful for eventual technological applications of BECs, such as for gyroscopes for ultraprecise navigation, very accurate atomic clocks, or other devices that use atom interferometry. (K. E. Strecker et al., Nature 417, 150, 2002 http://dx.doi.org/10.1038/nature747 ; L. Khaykovich et al., Science 296, 1290, 2002 http://dx.doi.org/10.1126/science.1071021 .)