The employ of a noiseless linear amplifier (NLA) has been proven as a useful tool for mitigating imperfections in quantum channels. Its analysis is usually conducted within specific frameworks, for which the set of input states for a given protocol is fixed. Here we obtain a more general description by showing that a noisy and lossy Gaussian channel followed by a NLA has a general description in terms of effective channels. This has the advantage of offering a simpler mathematical description, best suitable for mixed states, both Gaussian and non-Gaussian. We investigate the main properties of this effective system, and illustrate its potential by applying it to loss compensation and reduction of phase uncertainty.
@article{arxiv.1407.6798,
title = {Noiseless Linear Amplification and Quantum Channels},
author = {Rémi Blandino and Marco Barbieri and Philippe Grangier and Rosa Tualle-Brouri},
journal= {arXiv preprint arXiv:1407.6798},
year = {2015}
}