Efficient three-to-one entanglement purification protocol

We present a new entanglement purification protocol on three copies of a state via two bilateral controlled-NOT operations. We show that one-round successful probability of our protocol is twice as large as that of the protocol by Feng et al. [Phys. Lett. A 271 (2000) 44], [8], and that our method can be applied to the existing best protocol so as to improve the efficiency.