Spontaneous creation of solitons by shock cooling sodium Bose-Einstein condensates
Summary
We study the formation of defects in a Bose-Einstein condensate as is described by the Kibble-Zurek mechanism. The mechanism describes the formation of defects when a second order phase transition is crossed at a finite rate. This is done by shock cooling or quenching the last part of the evaporative cooling process where the transition into the condensed state is made. This allows for the study of the amount of solitons formed as a function of the quench time with the ultimate goal of determining the critical exponents of the phase transition. The amount of solitons is predicted by the Kibble-Zurek mechanism to scale as the quench time to the power alpha, which we attempted to measure. The dynamics of solitons are also studied in order to determine the time scale on which they decay. This turns out to be in the order of 0.29 seconds, and thus an important factor, since we consider quench times in the order of seconds. When correcting for the decay on this timescale, it turns out that alpha is extremely sensitive to variations in the decay time and therefore we were not able to give conclusive evidence on a value for the exponent. Instead we estimate the value of alpha to be between 0.5 and 2, based on our measurements.