Security of quantum key distribution with intensity correlations

TL;DR

This paper develops a method to incorporate intensity correlations in the security analysis of decoy-state quantum key distribution, addressing a key vulnerability in high-speed systems and providing practical parameters for quantification.

Contribution

It introduces a general technique to include arbitrary intensity correlations into QKD security analysis, requiring only experimental quantification of two parameters.

Findings

The technique effectively accounts for intensity correlations in security proofs.

It simplifies the experimental assessment by focusing on two main parameters.

Provides a new derivation linking asymptotic and non-asymptotic secret key rates.

Abstract

The decoy-state method in quantum key distribution (QKD) is a popular technique to approximately achieve the performance of ideal single-photon sources by means of simpler and practical laser sources. In high-speed decoy-state QKD systems, however, intensity correlations between succeeding pulses leak information about the users' intensity settings, thus invalidating a key assumption of this approach. Here, we solve this pressing problem by developing a general technique to incorporate arbitrary intensity correlations to the security analysis of decoy-state QKD. This technique only requires to experimentally quantify two main parameters: the correlation range and the maximum relative deviation between the selected and the actually emitted intensities. As a side contribution, we provide a non-standard derivation of the asymptotic secret key rate formula from the non-asymptotic one, in so revealing a necessary condition for the significance of the former.