Temperature-induced miscibility of impurities in trapped Bose gases

We study the thermal properties of impurities embedded in a repulsive Bose gas under a harmonic trapping potential. In order to obtain exact structural properties in this inhomogeneous many-body system, we resort to the path-integral Monte Carlo method. We find that, at low temperatures, a single impurity is expelled to the edges of the bath cloud if the impurity-boson coupling constant is larger than the boson-boson one. However, when the temperature is increased, but still in the Bose-condensed phase, the impurity occupies the core of the trap and, thus, the system becomes miscible. This thermal-induced miscibility transition is also observed for a finite concentration of impurities in this inhomogeneous system. We find that the transition temperature for miscibility depends on the impurity-boson interaction and we indicate a novel nondestructive method to measure the temperature of a system based on the studied phenomenon.