Berry' s phase of entangled spin pair E. Sjoqvist, Pra 62, 022109(2000 without inter-subsystem coupling) Separable pair, total BP=sum over individual BP For entangled pair, with one particle driven by the external magnetic field Initial state|H()≥=c0s个+sia geometric phase O. =T(cos a cos 8-1) B 6=arc cos[cos a cos g]10 Berry’s phase of entangled spin pair E. Sjoqvist, PRA 62, 022109(2000)(without inter-subsystem coupling) • Separable pair, total BP=sum over individual BP. • For entangled pair, with one particle driven by the external magnetic field | (0) cos | sin | 2 2   •Initial state   =  +  (cos cos 1)     g = − •Geometric phase    B  S  '    = arc cos[cos cos ]