Vortex-sound interactions in Bose-Einstein condensates
In a quantum fluid, such as an atomic Bose-Einstein condensate (BEC) or superfluid Helium, vortices are fundamental nonlinear excitations of the system. These structures possess quantized circulation and a "core" of vanishing density. In the limit of zero temperature and for a uniform quantum fluid, sound waves are the low-lying excitations of the system and provide the only energy sink for vortex decay.
We are studying how and why these vortices emit sound and decay. Sound emission can occur during the reconnection of vortex lines . More simply, the acceleration of a vortex also leads to sound emission. For example, a vortex precessing in a harmonically trapped condensate emits spiral sound waves  (below, left), as does a co-rotating vortex pair (below, right) .
As well as sound emission, we are also studying how vortices absorb sound. This is particularly relevant in trapped condensate, where any emitted sound is forced to reinteract with the vortex. For example, in a double trap geometry we have demonstrated that vortices can exchange energy with each other over long-range via the mutual emission and absorption of sound waves . This causes the vortices with spiral in and out of their wells in anti-phase, as shown below:
- Sound Emission due to Superfluid Vortex Reconnections, M. Leadbeater, T. Winiecki, D. C. Samuels, C. F. Barenghi, and C. S. Adams, Phys. Rev. Lett. 86, 1410 (2001)
Controlled Vortex-Sound Interactions in Atomic Bose-Einstein Condensates, N. G. Parker, N. P. Proukakis, C. F. Barenghi, and C. S. Adams, Phys. Rev. Lett. 92, 160403 (2004)
Decay of quantized vorticity by sound emission, C. F. Barenghi, N. G. Parker, N. P. Proukakis and C. S. Adams, J. Low Temp. Phys. 138, 629 (2005)
Coherent cross talk and parametric driving of matter-wave vortices, N. G. Parker, A. J. Allen, C. F. Barenghi, and N. P. Proukakis, Phys. Rev. A 86, 013631 (2012)