Entanglement-based quantum key distribution with non-Gaussian continuous variables

TL;DR

This paper explores how adding single photons to entangled states enhances quantum key distribution by increasing secret key rates and distance, while also developing new analysis methods for non-Gaussian states.

Contribution

It introduces a technique for photon addition to entangled states and demonstrates its benefits for QKD, including improved key rates and robustness against decoherence.

Findings

Photon addition distills entanglement and increases key rates.

Non-Gaussian correlations require new analysis methods.

Photon addition protects against decoherence.

Abstract

Addition of single photons to two-mode-squeezed-vacuum states has the effect of distilling quantum entanglement, and, when deployed in quantum key distribution, should lead also to an increase in the secret key rate. However, the extraction of secret keys from non-Gaussian entangled states is a complex issue and is at present not fully understood. In this paper we describe a technique for adding photons to entangled states, and demonstrate how it leads to an increase in secret key rates and the maximal distance for which keys can be distributed assuming asymptotic conditions. The quantum correlations thus produced were found to be of a highly non-Gaussian character, such that the Gaussian extremity principle returns a negative keyrate and effectively kills the protocol; we have therefore developed methods of analysis that do not require prior assumptions about the state. Although it could have been that the addition of single photons would make the system more fragile, this turned out not to be the case. Rather, the addition of a single photon was found to protect the protocol against both passive and active decoherence.