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

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.