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A quantum gate between a flying optical photon and a single trapped atom

Nature volume 508, pages 237240 (10 April 2014) | Download Citation

Abstract

The steady increase in control over individual quantum systems supports the promotion of a quantum technology that could provide functionalities beyond those of any classical device. Two particularly promising applications have been explored during the past decade: photon-based quantum communication, which guarantees unbreakable encryption1 but which still has to be scaled to high rates over large distances, and quantum computation, which will fundamentally enhance computability2 if it can be scaled to a large number of quantum bits (qubits). It was realized early on that a hybrid system of light qubits and matter qubits3 could solve the scalability problem of each field—that of communication by use of quantum repeaters4, and that of computation by use of an optical interconnect between smaller quantum processors5,6. To this end, the development of a robust two-qubit gate that allows the linking of distant computational nodes is “a pressing challenge”6. Here we demonstrate such a quantum gate between the spin state of a single trapped atom and the polarization state of an optical photon contained in a faint laser pulse. The gate mechanism presented7,8 is deterministic and robust, and is expected to be applicable to almost any matter qubit. It is based on reflection of the photonic qubit from a cavity that provides strong light–matter coupling. To demonstrate its versatility, we use the quantum gate to create atom–photon, atom–photon–photon and photon–photon entangled states from separable input states. We expect our experiment to enable various applications, including the generation of atomic9 and photonic10 cluster states and Schrödinger-cat states11, deterministic photonic Bell-state measurements12, scalable quantum computation7 and quantum communication using a redundant quantum parity code13.

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Acknowledgements

This work was supported by the European Union (Collaborative Project SIQS) and by the Bundesministerium für Bildung und Forschung via IKT 2020 (QK_QuOReP).

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Affiliations

  1. Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Strasse 1, 85748 Garching, Germany

    • Andreas Reiserer
    • , Norbert Kalb
    • , Gerhard Rempe
    •  & Stephan Ritter

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Contributions

All authors contributed to the experiment, the analysis of the results and the writing of the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Gerhard Rempe.

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https://doi.org/10.1038/nature13177

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