Finite-range multiplexing enhances quantum key distribution via quantum repeaters

TL;DR

This paper extends quantum repeater multiplexing to short-range connections, deriving formulas and showing that finite-range multiplexing significantly improves quantum key distribution rates similarly to full-range multiplexing.

Contribution

It introduces a short-range multiplexing protocol for quantum repeaters, providing analytical formulas and optimizing memory requirements to enhance quantum key distribution.

Findings

Finite-range multiplexing achieves similar benefits to full-range multiplexing.

Analytical formulas for repeater rate are derived for short-range connections.

Optimal matching protocols minimize quantum memory requirements.

Abstract

Quantum repeaters represent one possible way to achieve long-distance quantum key distribution. Collins et al. in [Phys. Rev. Lett. 98, 060502 (2007)] proposed multiplexing as method to increase the repeater rate and to decrease the requirement in memory coherence time. Motivated by the experimental fact that long-range connections are practically demanding, in this paper we extend the original quantum repeater multiplexing protocol to the case of short-range connection. We derive analytical formulas for the repeater rate and we show that for short connection lengths it is possible to have most of the benefits of a full-range multiplexing protocol. Then we incorporate decoherence of quantum memories and we study the optimal matching for the Bell-state measurement protocol permitting to minimize memory requirements. Finally, we calculate the secret key rate and we show that the improvement via finite-range multiplexing is of the same order of magnitude as via full-range multiplexing.