(2) EPP based on linear optical elements Alice Bob a3 a1 Pair 1 b1 b3 PBS PBS +/a4 82 Pair 2 b2 b4 Classical communication ab(中+ pab=F|+)ab(++(1-F)y+)ab(+ (HaH)b+valv)b) b (Have+Va h)b J w Panet al., Nature 410, 1067(2001)(2) EPP based on linear optical elements J. W. Pan et al., Nature 410, 1067 (2001)