Quench dynamics of 2D Bose gases across the BKT critical point

We report on the observation of non-equilibrium dynamics in 2D quantum systems across a critical point. We quench the system by coherently splitting a single 2D Bose gas into two, resulting in the dynamical crossing of the Berezinskii-Kosterlitz-Thouless phase transition. We monitor the relaxation dynamics towards the vortex-proliferated disordered phase using a matter-wave interferometry technique and find the time evolution of the phase correlation function and vortex density. We identify that the temporal decay of the correlation is related to the energy scale associated with vortex excitations. We further compare measured vortex unbinding dynamics with the real-time renormalisation group theory.

We acknowledge close collaboration with Professor Ludwig Mathey, Dr Vijay Singh (University of Hamburg, Germany) and Dr Junichi Okamoto (University of Freiburg, Germany) on the theoretical interpretation of this experimental work including extensive numerical simulation of specific cases.