Robustness of quantum communication based on a decoherence-free subspace using a counter-propagating weak coherent light pulse

摘要

We study distribution schemes for a polarization entangled photon pair basedon a decoherence-free subspace over lossy quantum channels and propose anefficient scheme that is robust against not only collective phase noises butalso general collective noises for two qubits. While the proposed schemeemploys two photons to build the decoherence-free subspace, the successprobability is proportional to the channel transmittance of a single photonwith the aid of a counter-propagating weak coherent light pulse. The keyingredient in the scheme is found to be the reciprocity of the channel. Theproposed scheme shares the rest of the properties with the previously proposedschemes, i.e., it can be realized by linear optical elements and it is robustagainst the fluctuations in the optical circuits used by the two parties.