Quantum repeaters and quantum key distribution: analysis of secret key rates

TL;DR

This paper compares different quantum repeater protocols to evaluate their effectiveness in enabling long-distance quantum key distribution, focusing on secret key rates and the impact of experimental imperfections.

Contribution

It provides a detailed analysis of multiple quantum repeater schemes, identifying key experimental parameters and their thresholds for secure key generation.

Findings

Identifies minimal parameter values for nonzero secret key rates.

Analyzes the impact of device imperfections on key rates.

Determines optimal rounds of entanglement purification.

Abstract

We analyze various prominent quantum repeater protocols in the context of long-distance quantum key distribution. These protocols are the original quantum repeater proposal by Briegel, D\"ur, Cirac and Zoller, the so-called hybrid quantum repeater using optical coherent states dispersively interacting with atomic spin qubits, and the Duan-Lukin-Cirac-Zoller-type repeater using atomic ensembles together with linear optics and, in its most recent extension, heralded qubit amplifiers. For our analysis, we investigate the most important experimental parameters of every repeater component and find their minimally required values for obtaining a nonzero secret key. Additionally, we examine in detail the impact of device imperfections on the final secret key rate and on the optimal number of rounds of distillation when the entangled states are purified right after their initial distribution.