An Exploration of the Physics of Entangled Photon States, and their Utility in Key Distribution Protocols

Abstract

In this experiment, a partial implementation of the BB84 protocol (Charles Bennett and Gilles Brassard, 1984) is conducted to study the nature of entangled photons. A 405 nm, 50 mW laser was used to shoot a beam of photons into a Barium Borate crystal This created two beams of IR, polarization entangled photons, which were detected using two single photon detectors and an Altera FPGA for coincidence counts. By changing the orientation of two half-wave plates, one at each detector, one can simulate the transfer of bits between two parties, Alice, and Bob. By introducing an eavesdropper in the form of a quartz plate on a rotating mount, we were able to show that the eavesdropper alters the state of the photons such that there is a roughly 50% reduction in coincidence counts, agreeing with our predictions.