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Colloquia

ics Colloquium
Friday, October 25, 2002
4:00 PM
Physics Building, Room 204
Note special time.
Randy Hulet [Host: Cass Sackett]
Rice University
"Tunable Interactions in Ultracold Bose and Fermi Gases - Solitons to Superfluids"
ABSTRACT:
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 [1]. A similar experiment was performed in Paris [2]. 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. [1] K.E. Strecker, G.B. Partridge, A.G. Truscott, R.G. Hulet Nature 417, 150 (2002). [2] L. Khaykovich et al., Science 296, 1290 (2002).

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