Effect of source statistics on utilizing photon entanglement in quantum key distribution

TL;DR

This paper presents a workflow for evaluating the quality of entanglement sources in quantum key distribution, highlighting the trade-offs and limitations due to multiphoton effects in SPDC sources.

Contribution

It introduces a new characterization workflow for entanglement sources and quantifies the secure key rate limits for SPDC sources compared to ideal single-pair sources.

Findings

Secure key rate limited to 0.029 bits per detection window for SPDC sources

Existence of an optimal gain for continuous-wave down-conversion sources

Comparison showing bounds of SPDC sources against ideal single-pair sources

Abstract

A workflow for evaluation of entanglement source quality is proposed. Based on quantum state density matrices obtained from theoretical models and experimental data, we make an estimate of a potential performance of a quantum entanglement source in quantum key distribution protocols. This workflow is showcased for continuously pumped spontaneous parametric down-conversion (SPDC) source, where it highlights the trade-off between entangled pair generation rate and entanglement quality caused by multiphoton nature of the generated quantum states. We employ this characterization technique to show that secure key rate of down-converted photon pairs is limited to 0.029 bits per detection window due to intrinsic multiphoton contributions. We also report that there exists one optimum gain for continuous-wave down-conversion sources. We find a bound for secure key rate extracted from SPDC sources and make a comparison with perfectly single-pair quantum states, such as those produced by quantum dots.