Frequency-Resolved Simulations of Highly Entangled Biphoton States: Beyond the Single-Pair Approximation. II. Application to Entanglement-based Quantum Key Distribution

TL;DR

This paper develops advanced frequency- and time-resolved simulations for entangled biphoton states in quantum key distribution, accurately modeling multi-pair events and imperfections to improve understanding of system performance.

Contribution

It introduces a systematic simulation approach using covariance matrix expansions to evaluate multi-pair effects in entanglement-based QKD.

Findings

Simulations agree with experimental key rates and error rates.

Multi-pair events significantly impact QKD performance.

The method efficiently incorporates spectral and setup imperfections.

Abstract

We present time- and frequency-resolved simulations of quantum key distribution~(QKD) systems employing highly entangled biphoton quantum states. Our simulations are based on expansions of the covariance matrix and photon detection probabilities of biphoton states in terms of increasing orders of the joint spectral amplitude that were introduced in the first part of this series. Employing these expansions allows us to efficiently evaluate the impact of multi-pair events on the performance of the QKD systems while systematically taking into account effects from the photon spectra and many relevant imperfections of the setup. The results are shown to be in agreement with corresponding measurements of the key rates and quantum bit error rates.