Strategies for achieving high key rates in satellite-based QKD

Sebastian Ecker,Matthias Fink,Thomas Scheidl,Johannes Handsteiner,Fabian Steinlechner,Rupert Ursin,Anton Zeilinger,Dominik Rauch,Bo Liu

doi:10.1038/s41534-020-00335-5

Abstract

Quantum key distribution (QKD) is a pioneering quantum technology on the brink of widespread deployment. Nevertheless, the distribution of secret keys beyond a few 100 km at practical rates remains a major challenge. One approach to circumvent lossy terrestrial transmission of entangled photon pairs is the deployment of optical satellite links. Optimizing these non-static quantum links to yield the highest possible key rate is essential for their successful operation. We therefore developed a high-brightness polarization-entangled photon pair source and a receiver module with a fast steering mirror capable of satellite tracking. We employed this state-of-the-art hardware to distribute photons over a terrestrial free-space link with a distance of 143 km, and extracted secure key rates up to 300 bits per second. Contrary to fiber-based links, the channel loss in satellite downlinks is time-varying and the link time is limited to a few minutes. We therefore propose a model-based optimization of link parameters based on current channel and receiver conditions. This model and our field test will prove helpful in the design and operation of future satellite missions and advance the distribution of secret keys at high rates on a global scale.

Highlights

Secure communications and data protection are the quintessential resources in an information-based society, with a wide range of applications such as financial transactions, ensuring personal privacy, and maintaining the integrity of critical infrastructure in the Internet of things
In order to be forearmed for future satellite down-link experiments, we have developed a quantum ground receiver for polarization-based Quantum key distribution (QKD) protocols, which is compatible with most existing optical ground stations (OGSs) with satellite tracking capabilities
All error rates are evaluated as arguments of the binary entropy function H2(x), with an error correction efficiency for the low-density parity-check (LDPC) code of f(x) = 1.2

Summary

Introduction

Secure communications and data protection are the quintessential resources in an information-based society, with a wide range of applications such as financial transactions, ensuring personal privacy, and maintaining the integrity of critical infrastructure in the Internet of things. The installation of quantum hardware on space platforms would provide a platform for fundamental physics experiments[8,9] and radically new technologies such as quantum clock synchronization[10,11,12] and quantum metrology[13] While this is a technologically immensely challenging task, a number of experimental[14,15,16,17,18,19,20,21] and theoretical[6,22] studies have established the feasibility of this vision with stateof-the-art technology available on ground and certified for operation in space. In what has been called the quantum space race[23], a number of international research groups in Canada, China, Europe, Japan, and Singapore are pursuing first missions involving space links[24,25], with first dedicated satellite transmitter payloads successfully launched into space[26,27,28,29,30]

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