13.如图,在平行六面体ABCD−A1B1C1D1ABCD-A_{1}B_{1}C_{1}D_{1}ABCD−A1B1C1D1中,底面ABCDABCDABCD是菱形,侧面A1ADD1A_{1}ADD_{1}A1ADD1是正方形,且∠A1AB=120∘\angle A_{1}AB=120\circ∠A1AB=120∘,∠DAB=60∘\angle DAB=60\circ∠DAB=60∘,AB=2AB=2AB=2,若PPP是C1DC_{1}DC1D与CD1CD_{1}CD1的交点,则AP=(AP=(AP=( )))