Recyclable amplification protocol for the single-photon entangled state

Photon loss is one of the main obstacles in long-distance quantum communication. In this letter, we put forward a highly efficient recyclable amplification protocol for protecting the single-photon entangled state. Different from all of the existing amplification protocols, by repeating the protocol, the discarded items can be reused to increase the success probability and the distilled new mixed state can be further amplified in a next round to increase its fidelity. In particular, this protocol is quite useful under high photon loss conditions. These features make our amplification protocol useful in future long-distance quantum communications.