Dependence of Δ η on the initial parameters of dual-species atomic clouds. (a) Δη versus initial velocity difference between ⁸⁵Rb and ⁸⁷Rb atomic clouds. (b) Δη versus initial position difference between ⁸⁵Rb and ⁸⁷Rb atomic clouds. The dot line is the data for ⁸⁵Rb and ⁸⁷Rb atomic clouds with size of 0.1 mm and temperature of 10 nK, the dash line is for 1 mm, 0.1 μK atomic clouds, the dash-dot line is for 3 mm, 3 μK atomic clouds, the solid line is for 3 mm, 3 μK ⁸⁵Rb atomic cloud and 5 mm, 3 μK ⁸⁷Rb atomic cloud.