Complex hybrid structures

Have been observed in a Bose–Einstein condensate (BEC). Researchers in Lene Hau’s laboratory at Harvard, using the technique of slowing and then stopping a light pulse in a BEC, sent two such pulses into a specially prepared BEC. They observed solitons, vortex rings, and their interactions, some of which created hybrids that were part vortex ring and part soliton. Never seen before, these bizarre BEC excitations sometimes opened up like an umbrella, then turned inside-out. Two such excitations could collide and form a spherical shell or, in some cases, annihilate each other. The image shows structures that arose after 2.8 ms of evolution in the trap. Hau and colleagues also performed computer simulations that correlate well with the experiments and thus help the researchers to understand the phenomenology. They say that their work will help physicists gain new insights into the superfluid phenomenon and into the breakdown of superconductivity. (N. S. Ginsberg, J. Brand, L. V. Hau, Phys. Rev. Lett. 94, 040403, 2005 http://dx.doi.org/10.1103/PhysRevLett.94.040403 .)