Security of quantum key distribution with multiphoton components

TL;DR

This paper analyzes the security of quantum key distribution protocols that utilize multiphoton components, extending the secure key extraction to up to four photons and improving error rate thresholds.

Contribution

It derives exact relations between secure key rate and error rates for six-state SARG04 protocol with multiphoton sources, enhancing security thresholds.

Findings

Higher secure bit error rate threshold for multiphoton components.

Exact relations between key rate and error rates for up to four photons.

Comparison showing improved performance over other protocols.

Abstract

Most qubit-based quantum key distribution (QKD) protocols extract the secure key merely from single-photon component of the attenuated lasers. However, with the Scarani-Acin-Ribordy-Gisin 2004 (SARG04) QKD protocol, the unconditionally secure key can be extracted from the two-photon component by modifying the classical post-processing procedure in the BB84 protocol. Employing the merits of SARG04 QKD protocol and six-state preparation, one can extract secure key from the components of single photon up to four photons. In this paper, we provide the exact relations between the secure key rate and the bit error rate in a six-state SARG04 protocol with single-photon, two-photon, three-photon, and four-photon sources. By restricting the mutual information between the phase error and bit error, we obtain a higher secure bit error rate threshold of the multiphoton components than previous works. Besides, we compare the performances of the six-state SARG04 with other prepare-and-measure QKD protocols using decoy states.