Oscillating soliton/vortex ring

The matter-wave interference between two initially-separated Bose-Einstein condensates was a landmark observation, demonstrating phase-coherence.  The collisional energy of the two condensates was sufficient that interactions between atoms could be neglected.  But what happens when the two condensates are separated by a very small distance, on the order of one healing length?  Interactions can no longer be neglected at such low collisional energies.  We created such a situation using our high-resolution imaging.  We observed that the matter wave interference pattern becomes a single pair of gray solitons.

The story does not end here.  It is generally known that a gray soliton is unstable in a 3D condensate.  It should decay into a vortex ring.  We found a different behavior, however.  In the elongated condensate, each of the two solitons evolves into a vortex ring, and then back into a soliton.  This process repeats periodically.  Such a periodic oscillation between two qualitatively different forms seems to be a rare phenomenon.

Related publication

• Shomroni, I., Lahoud, E., Levi, S. & Steinhauer, J.  Evidence for an oscillating soliton/vortex ring by density engineering of a Bose-Einstein condensate.  Nature Physics 5, 193 (2009).