Estimation of output-channel noise for continuous-variable quantum key distribution

Estimation of channel parameters is important for extending the range and increasing the key rate of continuous-variable quantum key distribution protocols. We propose an estimator for the channel noise parameter based on the method-of-moments. The method-of-moments finds an estimator from the moments of the output distribution of the protocol. This estimator has the advantage of being able to use all of the states shared between Alice and Bob. Other estimators are limited to a smaller publicly revealed subset of the states. The proposed estimator has a lower variance for the high-loss channel than what has previously been proposed. We show that the method-of-moments estimator increases the key rate by up to an order of magnitude at the maximum transmission of the protocol.