Decoy State Quantum Key Distribution With More Than Three Types Of Photon Intensity Pulses

TL;DR

This paper introduces an improved decoy state method for quantum key distribution that uses more than three photon intensity levels, significantly enhancing the accuracy of detection rate estimates and increasing the key rate.

Contribution

It proposes a novel experimentally feasible approach employing multiple photon intensities to improve estimation accuracy in decoy state QKD, surpassing previous methods with three intensities.

Findings

Estimates of detection and error rates are improved by over 20% on average.

Using more than three photon intensities enhances numerical stability of bounds.

The method is experimentally feasible and applicable to realistic QKD settings.

Abstract

Decoy state method closes source security loophole in quantum key distribution (QKD) using laser source. In this method, accurate estimates of the detection rates of vacuum and single photon events plus the error rate of single photon events are needed to give a good enough lower bound of the secret key rate. Nonetheless, the current estimation method for these detection and error rates, which uses three types of photon intensities, is accurate up to about 1% relative error. Here I report an experimentally feasible way that greatly improves these estimates and hence increases the one-way key rate of the BB84 QKD protocol with unbiased bases selection by at least 20% on average in realistic settings. The major tricks are the use of more than three types of photon intensities plus the fact that estimating bounds of the above detection and error rates is numerically stable although these bounds are related to the inversion of a high condition number matrix.