supported by the National Natural Science Foundation of China (Grant Nos.10774088,10675086,10875081,and 10871227);the National Basic Research Program of China(Grant No.2004CB318000)
We show that although we cannot distil a singlet frora many pairs of bound entangled states, the concurrence and the tangle of two entangled quantum states are always strictly larger than those of one of them, even bo...