Key reconciliation in quantum key distribution

Key reconciliation in quantum key distribution is studied in this report. After the transfer of single photons on the quantum channel there will inevitably be errors due to system imperfections and possibly eavesdropping. These errors must be removed for the final key to be useful. This is done with error correction over a classical channel. A potential eavesdropper can gain information about the key both from the quantum and the classical transmission. The eavesdropper´s information can be reduced to be arbitrary small in a final privacy-amplification step, where bits in the key are sacrificed to achieve the privacy. This report presents an extensive analysis of different error-correcting codes. Four protocols for error correction have been implemented: Cascade, Yamamura and Ishizuka´s, Low Density Parity-Check Codes and Winnow. Their performances have been evaluated by Monte-Carlo simulations. The number of final key bits after correction and privacy amplification, the probability of correcting all errors and the amount of information-exchange required to correct all errors have been analyzed for the different protocols. It is concluded that three of the different protocols each have characteristics that make them good choices in different setups. Only Yamamura and Ishizuka´s protocol is unsuitable for a real system.