Bose-Einstein condensation of ultracold atomic gases, first achieved
only seven years ago, has lead to remarkable demonstrations of matter
wave phenomena. One of the most compelling aspects of ultracold atoms
is the experimental ability to alter the strength and even the sign of
the interactions between atoms using magnetically tuned "Feshbach
resonances". We have exploited this tunability to create matter wave
solitons composed of Bose-Einstein condensates of lithium atoms . A
similar experiment was performed in Paris . Soliton waves arise when
a nonlinearity exactly compensates for wavepacket dispersion. This
compensation enables a soliton to propagate without spreading. Solitons
are observed in a variety of physical systems, including water waves,
plasma waves, and optical pulses, to name but a few. The nonlinearity
in ultracold atoms arises from their interactions. By changing the
interactions from repulsive to attractive, the condensate is observed to
form a multi-soliton "train" of up to 15 individual solitons. The
solitons maintain their size and shape for a propagation time of up to 3
s. Adjacent solitons are observed to interact repulsively.
We are also pursuing the possibility of creating Cooper pairs of
fermionic 6Li atoms, which would be an atom analog of superconductivity,
in the gas phase. The necessary attraction would again be generated
using a Feshbach resonance, which could enable the first exploration of
superconductivity in the strong coupling regime.
 K.E. Strecker, G.B. Partridge, A.G. Truscott, R.G. Hulet Nature 417,
 L. Khaykovich et al., Science 296, 1290 (2002).