Processing Entangled Links Into Secure Cryptographic Keys

TL;DR

This paper presents a comprehensive analysis of entangled link processing in quantum key distribution, optimizing measurement bases and entanglement distillation to enhance secure key rates.

Contribution

It introduces a unified formalism for the entire processing chain, including a new strategy and optimal entanglement distillation insights.

Findings

Proof of measurement basis conditions for Werner states to achieve secret key capacity

Comparison of a new processing strategy with existing methods

Quantitative relation between entanglement quality and secure key rate

Abstract

The following paper presents a holistic approach to the processing of entangled links within entanglement based quantum key distribution protocols, whose security relies on the Bell inequality. We investigate the interactions, and the collective impact, of the whole processing chain on the final secure key rate. This includes the quantum mechanical preprocessing in the form of entanglement distillation, processing of the entangled states via measurements and the necessary classical postprocessing based on the measurement results. Our investigations are based on the principle idea of the Eckert 1991 protocol and utilize the secret key capacity introduced by Devetak and Winter in 2005. Our results include a proof on what measurement bases need to be chosen to achieve this capacity for the case of Werner states. It also presents a new processing strategy and compares it with the most common one that can be found within the literature. Furthermore, it answers the question on how much entanglement distillation is optimal. By doing so we propose a unified formalism, describing the whole processing chain, that can be used to make quantitative statements on the relation between the quality and quantity of entangled but noisy quantum states used for generating secure keys.