Fig. 2

Collisional pumping of the spin of the ion. Sr⁺ ion spin projection on the \(\left| \downarrow \right\rangle _{{\mathrm{Sr}}^ + }\) state, P(↓), as function of number of Langevin collisions (time). In blue (red) the ion is prepared in the \(\left| \uparrow \right\rangle _{{\mathrm{Sr}}^ + }\) \(\left( {\left| \downarrow \right\rangle _{{\mathrm{Sr}}^ + }} \right)\) spin-state. The atoms are prepared in state \(\left| {1, - 1} \right\rangle _{{\mathrm{Rb}}}\) (a) or \(\left| {1,0} \right\rangle _{{\mathrm{Rb}}}\) (b). Insets show energetically allowed and forbidden spin-exchange processes. Error bars represent 1 SD