Robust and efficient quantum communication based on decoherence-free subspace

英敏 熊谷

Peng Xue

Dylan H. Mahler, Lee A. Rozema, Ardavan Darabi +1 more

Characterizing a quantum process is the critical first step towards applying such a process in a quantum information protocol. Full process characterization is known to be extremely resource-intensive, motivating the search for more efficient ways to extract salient information about the process. An example is the identification of ``decoherence-free subspaces,'' in which computation or communications may be carried out, immune to the principal sources of decoherence in the system. Here we propose and demonstrate a protocol which enables one to directly identify a decoherence-free subspace (DFS) without carrying out a full reconstruction. Our protocol offers an up-to-quadratic speedup over standard process tomography. In this paper, we experimentally identify the DFS of a two-qubit process with 32 measurements rather than the usual 256, characterize the robustness and efficiency of the protocol, and discuss its extension to higher-dimensional systems.

Hidetoshi Kumagai, Takashi Yamamoto, Masato Koashi +1 more

We study distribution schemes for a polarization entangled photon pair based on a decoherence-free subspace over lossy quantum channels and propose an efficient scheme that is robust against not only collective phase noises but also general collective noises for two qubits. While the proposed scheme employs two photons to build the decoherence-free subspace, the success probability is proportional to the channel transmittance of a single photon with the aid of a counter-propagating weak coherent light pulse. The key ingredient in the scheme is found to be the reciprocity of the channel. The proposed scheme shares the rest of the properties with the previously proposed schemes; i.e., it can be realized by linear optical elements and it is robust against the fluctuations in the optical circuits used by the two parties.

Siyu Song, Chuan Xi Wang

Rikizo Ikuta, Yohei Ono, Toshiyuki Tashima +5 more

We propose and demonstrate a scheme for boosting up the efficiency of entanglement distribution based on a decoherence‐free subspace (DFS) over lossy quantum channels. Our scheme achieves an entanglement‐sharing rate that is proportional to the transmittance of the quantum channel in spite of encoding qubits in multipartite systems for the DFS.