Quantum key distribution (QKD) is a two step protocol. In one step, quantum states are exchanged between two parties, usually called Alice and Bob. Afterwards, quantum correlations and classical communication are used to generate a shared secret key. In this paper, we focus on the exchange of quantum states with a prototype setup and present estimated secret bit rates. The continuous-variable QKD protocol [1-3] employs binary encoding in optical coherent states and postselection. In our experiment, the protocol is adapted to a long range fibre-based setup at the telecommunication wavelength (1550nm). The system employs heterodyne detection, using free-space optics and exploiting the polarisation degree of freedom. This allows for measuring the Q-functions of the transmitted signal states and the estimation of the secret key rates for different fibre lengths.

© 2009 IEEE

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