Spontaneous defect formation in inhomogeneous trapped Bose gases

Kibble-Zurek mechanism (KZM) provides a universal framework for describing the spontaneous defect formation in a system undergoing a continuous phase transition. Its extension to inhomogeneous systems is an interesting problem because the defect formation dynamics might be affected by the competition between the phase front propagation and the characteristic speed of sound of the system, and recently, it was predicted that the Kibble-Zurek (KZ) scaling exponent would be significantly modified by the trapping geometry of the system. In this poster, we describe our experimental study of the spontaneous vortex formation using trapped Bose gases of 87Rb and present the measurement results of the KZ exponent for various trapping potentials. Using a clipped Gaussian optical dipole trap, we controlled the aspect ratio and flatness of the trapping potential and observed the KZ exponent is changed accordingly but surprisingly, in an opposite direction to the theoretical prediction. We will discuss the implications of our observation on the inhomogeneous KZM and suggest directions for further investigations.