The Singapore protocol [for quantum cryptography]

The qubit protocol for quantum key distribution presented in this talk is fully tomographic and more efficient than other tomographic protocols. Under ideal circumstances the efficiency is log2(4/3) = 0.415 key bits per qubit sent, which is 25% more than the efficiency of 1/3 = 0.333 for the standard 6-state protocol. One can extract 0.4 key bits per qubit by a simple two-way communication scheme, and can so get close to the information-theoretical limit. The noise thresholds for secure key bit generation in the presence of unbiased noise will be reported and discussed. (author)