The security of practical post-selection in Gaussian-modulated continuous-variable quantum key distribution

Gaussian-modulated coherent-state (GMCS) continuous-variable quantum key distribution (CVQKD) offers a practical path to quantum-secured communication owing to its compatibility with existing optical fibre networks and use of mature security proofs. Achieving high secret key rates in real-time systems, however, requires post-processing schemes that are both informationtheoretically efficient and computationally scalable. In previous experimental work1 , we have demonstrated record real-time key rates using a one-round sliced reconciliation scheme with guardband post-selection. Here, we present the corresponding theoretical framework and provide an asymptotic security analysis that considers arbitrary collective attacks, a much broader class of attacks than the usually assumed Gaussian collective attacks. The security analysis applies the entropic continuity of quantum channels justi fied by a quantum channel estimation procedure. In conditions of high noise, our scheme uses 500 times less classical communication than multidimensional reconciliation.