A prototype of a free-space QKD scheme based on the B92 protocol

We describe the architecture of QuAKE (Quantum Advanced Key Exchanger), an experimental setup for quantum key distribution (QKD) over a free-space quantum channel based on the B92 protocol [1]. The system consists of a transmitter (Alice) and a receiver (Bob) that are connected through a free-space quantum channel over a distance of approximately 50 m, and are each driven by a field-programmable gate array (FPGA). The raw key shared by Alice and Bob is processed in four subsequent steps (i.e., sifting, channel estimation, key reconciliation and privacy amplification) which are implemented in Matlab. Finally, public discussion is implemented with the user datagram protocol (UDP) transport protocol running over the Internet protocol (IP) network protocol, while 802.11g underlies the physical layer transmission.