Long-distance quantum key distribution with imperfect devices

TL;DR

This paper compares two probabilistic quantum repeater schemes for long-distance quantum key distribution, analyzing their performance under realistic device imperfections and identifying conditions for optimal secret key rates.

Contribution

It provides a detailed comparison of two quantum repeater protocols considering practical imperfections and determines the conditions for their optimal performance.

Findings

Identifies the maximum double-photon probability for secure key distillation.

Determines the crossover distance where repeater schemes outperform direct transmission.

Compares achievable secret key rates of the two protocols at optimal settings.

Abstract

Quantum key distribution over probabilistic quantum repeaters is addressed. We compare, under practical assumptions, two such schemes in terms of their secure key generation rates per quantum memory. The two schemes under investigation are the one proposed by Duan et al. in [Nat. 414, 413 (2001)] and that of Sangouard et al. in [Phys. Rev. A 76, 050301 (2007)]. We consider various sources of imperfection in both protocols, such as nonzero double-photon probabilities at the sources, dark counts in detectors, and inefficiencies in the channel, photodetectors and memories. We also consider memory decay and dephasing processes in our analysis. For the latter system, we determine the maximum value of the double-photon probability beyond which secretkey distillation is not possible. We also find the crossover distance beyond which the repeater schemes outperform the non-repeater ones. We finally compare the two protocols in terms of their achievable secret key generation rates at their optimal settings