Noiseless linear amplification and loss-tolerant quantum relay using coherent-state superpositions

Abstract

Noiseless linear amplification (NLA) is useful for a wide variety of quantum protocols. Here we propose a fully scalable amplifier which, for asymptotically large sizes, can perform perfect fidelity NLA on any quantum state. Given finite resources, however, it is designed to perform perfect fidelity NLA on coherent states and their arbitrary superpositions. Our scheme is a generalization of the multiphoton quantum scissor teleamplifier, which we implement using a coherent-state superposition resource state. Furthermore, we prove our NLA is also a loss-tolerant relay for multiary phase-shift keyed coherent states. Finally, we demonstrate that our NLA is also useful for continuous-variable entanglement distillation, even with realistic experimental imperfections.