Shocking Bose-Einstein Condensates with Slow Light
Lene Hau, Harvard University
Light pulses have been slowed in a Bose-Einstein condensate to only 17 m/s, more than seven orders of magnitude lower than the light speed in vacuum. Associated with the dramatic reduction factor for the light speed is a spatial compression of the pulses by the same large factor.
A light pulse, which is 1-2 miles long in vacuum, is compressed to a size of ~50 microns, and at that point it is completely contained within the atom cloud. This further allows the light pulse to be completely stopped and stored in the atomic medium, and subsequently regenerated with no loss.
With the most recent extension of the method, the /light roadblock/, light pulses have been compressed from 2 miles to only 1-2 microns.
This system has been used to generate the superfluid analogue of shock waves, Quantum Shock Waves, in Bose-Einstein condensates. These dramatic excitations result in the formation of solitons that in turn decay into quantized vortices - created far out of equilibrium, in pairs of opposite circulation - revealing directly the process of superfluid breakdown in Bose-Einstein condensates. With a double light-roadblock setup, we can generate controlled collisions between shock waves resulting in completely unexpected, nonlinear excitations. We have observed hybrid structures consisting of vortex rings embedded in dark solitonic shells. The vortex rings act as 'phantom propellers' leading to very rich excitation dynamics.
