  An important physical process unique to neutral-ion systems is the
charge-transfer (CT) reaction. Here, we present measurements of and models for
CT processes between co-trapped ultracold Ca atoms and Yb ions under
well-controlled conditions. The theoretical analysis reveals the existence of
three reaction mechanisms when lasers from a magneto-optical trap (MOT) and an
additional catalyst laser are present. Besides the direct CT involving existent
excited Ca population in the MOT, the second pathway is controlled by
MOT-induced CT, whereas the third one mostly involves the additional
red-detuned laser.
