Heavy solitons in a fermionic superfluid

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T. Yefsah, A. T. Sommer, M. J. H. Ku, L. W. Cheuk, W. Ji, W. S. Bakr and M. W. Zwierlein
Nature 499, 426-430 (2013)

Solitary waves that maintain their shape as they propagate, known as solitons, occur in many physical
systems, from water waves, to light pulses to quantum mechanical matter waves in superfluids and
superconductors. Solitons are highly nonlinear and localized, properties which make them very sensitive
probes of the medium in which they propagate.

In their work Yefsah and colleagues create long-lived solitons in a strongly interacting superfluid of
fermionic atoms. Intriguingly, as they tuned the interactions from the regime of Bose–Einstein condensation
towards the limit of long-range Cooper pairs, they found that the solitons’ effective mass increased
markedly, to more than 200 times their bare mass, some 50 times larger than the theoretically predicted
value. Their work thus provides a benchmark for theories of non-equilibrium strongly interacting fermions.