Abstract

Entanglement distillation is an efficient method to retrieve high-quality entanglement from a large number of noise-damped entanglement states. Many investigations on continuous variable entanglement distillation have focused on low-loss or medium-loss channels. Herein, we primarily study entanglement distillation in extremely lossy (total channel transmittance $\eta\ll 1$) or even near-zero transmittance ($\eta\approx 0$) channels. In particular, we analyze the manner in which entanglement and success probability decrease as $\eta\to 0$. The performances of conventional biside photon subtraction and one-time photon subtraction on two optical modes separated by $L$ km are investigated. The motivation for our study includes the recent advancements in twin-field quantum key distribution, wherein single-photon detection is sufficient to provide a useful private key. In the same vein, we propose an entanglement distillation scheme with an efficiency of $O(\sqrt\eta)$ using one-time photon subtraction and weak coherent state injection. Thus, our proposed scheme provides a method for distilling extremely damped entanglement states for continuous variable quantum information processing.

© 2020 Optical Society of America