Combining quantum key distribution and internetworking over a 12 km real-world fibre link

Quantum key distribution (QKD) is the only technique currently known that provides cryptographic key exchange over an untrusted public communication channel with information theoretic security [1]. We present the current status of our QKD system, which allows encoding of quantum bits into polarization states of light. The system includes decoy states to remove the threat of eavesdropping attacks based on photon-number-splitting in an efficient way [2], low-density parity-check-matrix based error correction [3], and is implemented on a 12 km fibre link between the University of Calgary and the Southern Alberta Institute of Technology. Two home-made circuits based on FPGAs are used to control the key distribution process and acquire the raw key bits. At the same time they allow the implementation of fast error correction and privacy amplification. Our system also allows sending of classical framing information via sequences of strong laser pulses, inspired by the Ethernet protocol, whose purpose comprise synchronization, sender and receiver identification, and assessment and compensation of time-varying birefringence in the communication channel.