  New near-capacity continuous-variable quantum key distribution (CV-QKD)
reconciliation schemes are proposed, where both the authenticated classical
channel (ClC) and the quantum channel (QuC) for QKD are protected by separate
forward error correction (FEC) coding schemes. More explicitly, a new
codeword-based - rather than syndrome-based - QKD reconciliation scheme is
proposed, where Alice sends an FEC-protected codeword to Bob through a ClC,
while Bob sends a separate FEC protected codeword to Alice through a QuC. Upon
decoding the codeword received from the other side, the final key is obtained
by applying a simple modulo-2 operation to the local codeword and the decoded
remote codeword. As a result, first of all, the proposed codeword-based QKD
reconciliation system ensures protection of both the QuC and of the ClC.
Secondly, the proposed system has a similar complexity at both sides, where
both Alice and Bob have an FEC encoder and an FEC decoder. Thirdly, the
proposed system makes QKD reconciliation compatible with a wide range of FEC
schemes, including polar codes, CCs and irregular convolutional codes (IRCCs),
where a near-capacity performance can be achieved for both the QuC and for the
ClC.Our simulation results demonstrate that thanks to the proposed regime, the
performance improvements of the QuC and of the ClC benefit each other, hence
leading to an improved secret key rate (SKR) that inches closer to both the
Pirandola-Laurenza-Ottaviani-Banchi (PLOB) bound and to the maximum achieveable
rate bound.
