Design and Testing of a Portable Interoperable Ground Station for Satellite Quantum Key Distribution

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Recently, Satellite-based Quantum Key Distribution (SatQKD) has been reported at distances
and rates well beyond what is feasible through fiber with current protocols and
technology. Satellite-based quantum communications require Optical Ground Stations
(OGSs) to receive or transmit quantum information. Mobile OGSs could provide weather-resilient
key services by moving sites to optimise conditions during communication and could also reactively
add to quantum receiving/transmitting capabilities within an area to match demand.
Portable ground stations can also enable flexible testing capabilities for air-, ground-, and seabased
QKD platforms.
In this thesis, I present the design and testing of the Portable Interoperable Ground Station
(PIGS) - the UK’s first receiver system for SatQKD. PIGS is designed for operation with two
planned UK-based SatQKD missions, and is able to interoperate with other existing/planned
missions. I highlight design trade-offs, and my analysis focuses on SatQKD-relevant metrics
including component Fields of View (FoVs), expected losses (internal and satellite-to-ground), and
expected key rates. I test QKD performance over a 520m free-space test range at the University of
Bristol’s Langford campus and measure a quantum bit error rate of 6.91%±1.04%; optical noise
is measured to be 0.44×1012 cps/sr · nm·m2 on a dark night, which is sufficient to perform QKD
despite proximity to the city of Bristol. I also analyse coarse satellite tracking performance and
find it to be fit for purpose. During testing and analysis, I found that the transmitted quantum
signals may be subject to arbitrary polarisation rotations during SatQKD operation. To correct
this, I have developed a novel method for measuring and compensating the expected rotations.
My method uses single-photon-level signals and requires the minimum necessary correction
optics added to a free-space BB84 measurement. Simulated performance indicates that PIGS
could successfully implement this method under the ∼ 40dB losses expected during operation,
though optical noise must be reduced from current levels.
Date of Award3 Oct 2023
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorSiddarth K Joshi (Supervisor) & John G Rarity (Supervisor)

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