Quantum repeaters in space

TL;DR

This paper proposes a satellite-based quantum repeater scheme that combines space and ground stations to enable global quantum entanglement distribution with higher efficiency and reliability than existing methods.

Contribution

It introduces a novel satellite-based quantum repeater architecture that outperforms traditional ground-based repeaters in key rate, reliability, and flexibility.

Findings

Higher secret key rates achieved compared to other architectures

Enhanced reliability and flexibility demonstrated in simulations

Feasibility analysis supports potential mid-term implementation

Abstract

Long-distance entanglement is a very precious resource, but its distribution is very difficult due to the exponential losses of light in optical fibres. A possible solution consists in the use of quantum repeaters, based on entanglement swapping or quantum error correction. Alternatively, satellite-based free-space optical links can be exploited, achieving better loss-distance scaling. We propose to combine these two ingredients, quantum repeaters and satellite-based links, into a scheme that allows to achieve entanglement distribution over global distances with a small number of intermediate untrusted nodes. The entanglement sources, placed on satellites, send quantum states encoded in photons towards orbiting quantum repeater stations, where entanglement swapping is performed. The performance of this repeater chain is assessed in terms of the secret key rate achievable by the BB-84 cryptographic protocol. We perform a comparison with other repeater chain architectures and show that our scheme is superior in almost every situation, achieving higher key rates, reliability and flexibility. Finally, we analyse the feasibility of the implementation in the mid-term future and discuss exemplary orbital configurations. The integration of satellite-based links with ground repeater networks can be envisaged to represent the backbone of the future Quantum Internet.