Quantum key distribution: defeating collective noise without reducing efficiency (pp0845-0856)
          Song Lin, Gong-De Guo, Fei Gao, and Xiao-Fen Liu
          doi: https://doi.org/10.26421/QIC14.9-10-9
Abstracts: Decoherence-free subspace (DFS) is a valid solution to realize quantum communication over a collective noise channel, and has been widely studied. Generally speaking, replacing a qubit with a DFS state will cause the reduction of communication efficiency. However, in this letter, it is shown that some kinds of noises may not lower the transmission rate of quantum key distribution. To illustrate it, we propose two quantum key distribution protocols based on Bell states. Here, two nonorthogonal and unbiased sets in a DFS are constructed by linear combination of particles at different positions. Since n − 1 classical bits are distributed by using 2n qubits in our protocols, the transmission rate is close to that of noiseless BB84 protocol. Furthermore, when considering the cost of transmitting classical bits, the efficiencies of these protocols are even higher than that of BB84 protocol.
Key words:  quantum key distribution, decoherence-free subspace, Bell states