title: Implementation of a quantum controlled-SWAP gate with photonic circuits.
abstract: Quantum information science addresses how the processing and transmission of information are affected by uniquely quantum mechanical phenomena. Combination of two-qubit gates has been used to realize quantum circuits, however, scalability is becoming a critical problem. The use of three-qubit gates may simplify the structure of quantum circuits dramatically. Among them, the controlled-SWAP (Fredkin) gates are essential since they can be directly applied to important protocols, e.g., error correction, fingerprinting, and optimal cloning. Here we report a realization of the Fredkin gate for photonic qubits. We achieve a fidelity of 0.85 in the computational basis and an output state fidelity of 0.81 for a 3-photon Greenberger-Horne-Zeilinger state. The estimated process fidelity of 0.77 indicates that our Fredkin gate can be applied to various quantum tasks.
authors.affiliation: Research Institute for Electronic Science, Hokkaido University, Sapporo 001-0020, Japan.|The Institute of Scientific and Industrial Research, Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan.
authors.forename: Takafumi
authors.initials: T
authors.lastname: Ono
authors.affiliation: Research Institute for Electronic Science, Hokkaido University, Sapporo 001-0020, Japan.|The Institute of Scientific and Industrial Research, Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan.|Kyoto University, Department of Electronic Science and Engineering, Kyoto Daigaku-Katsura, Nishikyo-ku, Kyoto 615-8510, Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Okamoto
authors.affiliation: Research Institute for Electronic Science, Hokkaido University, Sapporo 001-0020, Japan.|The Institute of Scientific and Industrial Research, Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan.
authors.forename: Masato
authors.initials: M
authors.lastname: Tanida
authors.affiliation: Graduate School of Advanced Sciences of Matter, Hiroshima University, Kagamiyama 1-3-1, Higashi Hiroshima 739-8530, Japan.
authors.forename: Holger F
authors.initials: HF
authors.lastname: Hofmann
authors.affiliation: Research Institute for Electronic Science, Hokkaido University, Sapporo 001-0020, Japan.|The Institute of Scientific and Industrial Research, Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan.|Kyoto University, Department of Electronic Science and Engineering, Kyoto Daigaku-Katsura, Nishikyo-ku, Kyoto 615-8510, Japan.
authors.forename: Shigeki
authors.initials: S
authors.lastname: Takeuchi