14.棱长为1的正方体ABCD−A1B1C1D1ABCD-A_{1}B_{1}C_{1}D_{1}ABCD−A1B1C1D1中,点PPP在棱CDCDCD上运动,点QQQ在侧面ADD1A1ADD_{1}A_{1}ADD1A1上运动,满足B1Q⊥B_{1}Q\botB1Q⊥平面AD1PAD_{1}PAD1P,则线段PQPQPQ的最小值为((( )))