This thesis describes the deployment of a free-space quantum keydistribution system across the University of Waterloo campus. Thequantum key distribution system has the ability to provideunconditionally secure communication between two parties: Alice andBob. The system exploits the quantum mechanical property ofentanglement in order to generate a key. Security is then guaranteedby the No-Cloning theorem and the laws of quantum mechanics whichprevent a quantum system from being measured without disturbing it.Polarization-entangled photon pairs are created using the non-linearoptical process of type-II spontaneous parametric down-conversion. Afree-space link of approximately $mathrm{580~m}$ is used todistribute one-half of the pairs to Alice at a distant location,while the other half of the pairs are locally detected by Bob. Thedetails of the detection apparatus necessary to measure thepolarization of the photons and the software used to process themeasurement data according to the BBM92 protocol are described. Anexperimental violation of the CHSH inequality (a derivative of theoriginal Bell inequality) is demonstrated to show thatpolarization-entangled photon pairs are in fact being distributed tothe two parties. Finally, the full BBM92 protocol is performed usingthe entangled photon pairs to generate a secure key and transmit anencrypted message between Alice and Bob. Currently, the system canonly be operated at night because background light saturates thedetectors during the day; however, future work will focus on makingdaylight operation feasible.
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On Free Space Quantum Key Distribution and its Implementation with a Polarization-Entangled Parametric Down Conversion Source
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