Cascaded noiseless linear amplification for single-photon state

Abstract: Photon loss is one of the main obstacles in current long-distance quantum communications. The approach of noiseless linear amplification (NLA) is one of the powerful way to distill the single-photon state (SPS) from a mixed state, which comprises both the SPS and vacuum state. However, existing NLA protocol can only perform the amplification for one time. That is the fidelity of the SPS cannot be increased anymore. In this paper, We put forward an efficient cascaded NLA protocol for both the SPS and single-photon entanglement (SPE), respectively, with the help of some auxiliary single photons. By repeating this protocol for sever times, the fidelity of the SPS and SPE can reach near 100\%, which may make this protocol is extremely useful to close the detection loophole in quantum key distribution. Moreover, this protocol is based on the linear optics, which makes it feasible in current technology.