#### Abstract

We revisit a classic study [D. S. Hall *et al.*, Phys. Rev. Lett. **81**, 1539 (1998)] of interpenetrating Bose-Einstein condensates in the hyperfine states $|F=1,{m}_{f}=-1\u27e9\equiv |1\u27e9$ and $|F=2,{m}_{f}=+1\u27e9\equiv |2\u27e9$ of ${}^{87}\mathrm{Rb}$ and observe striking new nonequilibrium component separation dynamics in the form of oscillating ringlike structures. The process of component separation is not significantly damped, a finding that also contrasts sharply with earlier experimental work, allowing a clean first look at a collective excitation of a binary superfluid. We further demonstrate extraordinary quantitative agreement between theoretical and experimental results using a multicomponent mean-field model with key additional features: the inclusion of atomic losses and the careful characterization of trap potentials (at the level of a fraction of a percent).

- Received 9 July 2007

DOI:https://doi.org/10.1103/PhysRevLett.99.190402

©2007 American Physical Society