Low cost, short range free space quantum cryptography for consumer applications
: pocket size for pocket change

  • David L D Lowndes

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)


A Quantum Key Distribution system has been demonstrated with a focus on applicability of the technology to a consumer use model. The optical devices were split into a large, expensive “Quantum ATM” (the Bob terminal) and a small, cheap handheld section (the Alice device).
Work was initially done to integrate the devices into a realistic demonstration system which was exhibited at several international conferences. Following this success, the devices constituent parts were isolated and improved upon. Work on the Alice device focused upon proposing a new scheme for light collimation and then investigating a method to enact this. In the Bob device the progress was directed towards a more effective single photon detection system utilizing active quenching.
An asymptotic secure key rate of 20kb/s was obtained at a bit error rate (BER) of 4% corresponding to a daylight operation scenario. A docking scheme was enacted to simplify the alignment of the optical channel which was shown to be repeatable over at least 50 cycles. The system was also shown to be stable over an extended period of time.
Date of Award11 Mar 2014
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorJohn G Rarity (Supervisor)

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