Impact of Limited Classical Channel Bandwidth on the Secret Key Rate of a CV-QKD System

Continuous-variable quantum key distribution (CV-QKD) can extract secret keys in an efficient and practical manner using off-the-shelf telecommunication equipment. This sets CV-QKD as a key technology for implementation in optical fiber networks already deployed in the field. Notwithstanding, the extraction of secret keys in CV-QKD requires the exchange of information, not only on a quantum channel, but also on an authenticated and public classical channel. The classical channel is required to exchange part of the coherent states to aid with the parameter estimation step to conclude on the secrecy of the extracted key, and to exchange side information essential to the reconciliation step. Here, we study the bandwidth demand of the information exchanged in the classical channel and how it can impact the extraction key rate of a CV-QKD system. The post-processing step consuming the highest bandwidth of the classical channel is the reconciliation step, due to the exchange of the side information. We consider different dimensions for the multidimensional reconciliation demanding different bandwidths on the classical channel and compute the allowed extraction key rate depending on the performance of the method, in terms of frame error rate.