On the deployment and testing of a quantum ground station for satellite Quantum Key Distribution

Abstract

Satellite-based Quantum Key Distribution (QKD) uses the fundamental properties of quantum mechanics to offer unparalleled security against eavesdroppers with the ability to scale quantum networks globally. Its use of quantum mechanics to protect information makes QKD the best choice currently for next generation secure communication systems. The implementation of satellite-based QKD still has many challenges to overcome before it becomes a widely used method of secure communication. This thesis discusses some fundamentals of classic cryptography and why moving towards quantum-based security protocols is necessary. We introduce a range of considerations for establishing a reliable long-distance free-space satellite optical link, thus allowing QKD to occur. Since a substantial amount of research has already been conducted on optical fiber communication for terrestrial links, our focus is specifically directed towards free space quantum links. While we discuss the protocols used with current experiments, we further focus the discussion around how background noise present in these free-space satellite channels can contribute to lower Signal-to-Noise Ratios (SNRs). Additionally, we experimentally measure background noise and light pollution expected at three quantum ground station locations: The University of Calgary, Rothney Astrophysical Observatory, and the University of Waterloo. The experimental measurements were taken at periods during which high atmospheric background noise was predicted. These measurements aim to show the anticipated background light during a downlink QKD experiment, when the ground station is used as a receiver and the satellite as a transmitter of quantum signals. To measure the expected background noise of an uplink QKD experiment, one for which the satellite is the receiver, we use the Visible Infrared Imaging Radiometer Suite Day-Night Band (VIIRS-DNB) instrument onboard the Suomi National Polar-orbiting Partnership (NPP) satellite. This satellite gives a spectra for a requested day in the 500 nm to 900 nm bandwidth. As many QKD experiments of interest fall within the upper range of this bandwidth, this satellite data is an excellent candidate for our analysis. In this thesis we show a comprehensive analysis of background noise and help find the background noise limit for future satellite-based QKD experiments, such as the upcoming Quantum Encryption and Science Satellite (QEYSSat).