The dimension reduction method enables security proofs of quantum key distribution (QKD) protocols that are originally formulated in infinite dimensions via reduction to a tractable finite-dimensional optimization. The reduction of dimensions is associated with a correction term in the secret key rate calculation. The previously derived correction term is loose when the protocol measurements are nearly block-diagonal with respect to the projection onto the reduced finite-dimensional subspace. Here, we provide a tighter correction term. It interpolates between the two extreme cases where all measurement operators are block-diagonal, and where at least one has maximally large off-diagonal blocks. This new correction term can reduce the computational overhead of applying the dimension reduction method by reducing the required dimension of the chosen subspace.
@article{arxiv.2210.14296,
title = {An Improved Correction Term for Dimension Reduction in Quantum Key Distribution},
author = {Twesh Upadhyaya and Thomas van Himbeeck and Norbert Lütkenhaus},
journal= {arXiv preprint arXiv:2210.14296},
year = {2022}
}