  We introduce a diversity extraction for multicarrier continuous-variable (CV)
quantum key distribution (QKD). The diversity extraction utilizes the resources
that are injected into the transmission by the additional degrees of freedom of
the multicarrier modulation. The multicarrier scheme granulates the information
into Gaussian subcarrier CVs and divides the physical link into several
Gaussian sub-channels for the transmission. We prove that the exploitable extra
degree of freedom in a multicarrier CVQKD scenario significantly extends the
possibilities of single-carrier CVQKD. The diversity extraction allows for the
parties to reach decreased error probabilities by utilizing those extra
resources of a multicarrier transmission that are not available in a
single-carrier CVQKD setting. The additional resources of multicarrier CVQKD
allow the achievement of significant performance improvements that are
particularly crucial in an experimental scenario.
