Beating direct transmission bounds for quantum key distribution with a multiple quantum memory station

TL;DR

This paper proposes an extension of a quantum key distribution protocol using multiple quantum memory pairs in parallel, significantly relaxing experimental requirements and enabling surpassing repeaterless bounds even in high-loss channels.

Contribution

It introduces a multi-memory extension to existing protocols, demonstrating how parallel operation reduces memory demands for beating repeaterless bounds.

Findings

Adding a few memory pairs enables crossing the repeaterless bound in high-loss channels.

Parallel operation of multiple memories relaxes the experimental parameters needed.

The protocol's effectiveness increases with the number of memory pairs.

Abstract

Overcoming repeaterless bounds for the secret key rate capacity of quantum key distribution protocols is still a challenge with current technology. D. Luong et al. [Applied Physics B 122, 96 (2016)] proposed a protocol to beat a repeaterless bound using one pair of quantum memories. However, the required experimental parameters for the memories are quite demanding. We extend the protocol with multiple pairs of memories, operated in a parallel manner to relax these conditions. We quantify the amount of relaxation in terms of the most crucial memory parameters, given the number of applied memory pairs. In the case of high-loss channels we found that adding only a few pair of memories can make the crossover possible.