Decoherence-protected memory for a single-photon qubit

Abstract

Distributed quantum computation in a quantum network1,2,3 is based on the idea that qubits can be preserved and efficiently exchanged between long-lived, stationary network nodes via photonic links4. Although long qubit lifetimes have been observed5,6,7,8,9,10, and non-qubit excitations have been memorized11,12,13,14, the long-lived storage and efficient retrieval of a photonic qubit by means of a light–matter interface15,16,17,18,19,20 remains an outstanding challenge. Here, we report on a qubit memory based on a single atom coupled to a high-finesse optical resonator. By mapping the qubit between an interface basis with strong light–matter coupling and a memory basis with low decoherence, we achieve a coherence time exceeding 100 ms with a time-independent storage-and-retrieval efficiency of 22%. The former constitutes an improvement by two orders of magnitude21,22 and thus implements an efficient photonic qubit memory with a coherence time that exceeds the lower bound needed for direct qubit teleportation in a global quantum internet.

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Fig. 1: Three different experimental protocols are employed for photonic qubit storage.
Fig. 2: Experimental set-up and level schemes for the single-atom quantum memory.
Fig. 3: Results for a memory experiment with mapping and remapping to and from the memory basis, respectively.
Fig. 4: Results for a memory experiment with the application of a spin-echo technique.

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Acknowledgements

We thank B. Wang for the development of the hardware and S. Dürr, L. Li and M. Uphoff for discussion. This work was supported by the Bundesministerium für Bildung und Forschung via the Verbund Q.comand by the Deutsche Forschungsgemeinschaft via the excellence cluster Nanosystems Initiative Munich (NIM).

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M.K., O.M., A.N., S.R. and G.R. conceived the experiment. M.K., O.M. and S.L. performed the experiment. M.K., O.M., S.L., S.R. and G.R. evaluated the data. All authors contributed to the writing of the manuscript.

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Correspondence to M. Körber.

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Körber, M., Morin, O., Langenfeld, S. et al. Decoherence-protected memory for a single-photon qubit. Nature Photon 12, 18–21 (2018). https://doi.org/10.1038/s41566-017-0050-y

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