Raman quantum memory of photonic polarized entanglement

Journal name:
Nature Photonics
Year published:
Published online


The storage of photonic entanglement is central to the achievement of long-distance quantum communication based on quantum repeaters and scalable linear optical quantum computation. Among the memory protocols reported to date, the Raman scheme has the advantages of being broadband and high-speed, resulting in a huge potential in quantum networks. To date there have been no reports on the storage of photonic polarized entanglement using the Raman protocol. Here, two storage experiments using the Raman scheme are reported: (1) heralded single-photon entanglement of the path and polarization storage in a cold atomic ensemble, and (2) polarization entanglement storage in two cold atomic ensembles. The experimental data clearly show that the quantum entanglement is preserved in this memory platform. Our work shows great promise for the establishment of quantum networks in high-speed communications.

At a glance


  1. Energy diagram and experimental set-up.
    Figure 1: Energy diagram and experimental set-up.

    a, Simplified energy level diagram and time sequence for the generation, storage and retrieval of polarization entanglement. H and V are the horizontal and vertical polarizations, respectively. P1 and P2 are modulated pulses with 25 ns (Δt) and 160 ns pulse widths, respectively, from two acoustic optic modulators. b, Simplified set-up. L and R refer to two SRS paths in MOT A. MOT, magneto-optical trap. PBS, polarization beamsplitter. λ/2, half-wave plate. λ/4, quarter-wave plate. S, Stokes photon. AS, anti-Stokes photon. D1, D2 and D3 are single-photon detectors 1, 2 and 3, respectively (PerkinElmer SPCM-AQR-15-FC). PD, home-made photoelectric detector. PZT, piezoelectric transducer. U and D are up and down optical modes input into MOT B, respectively. P, half-wave plate. θ, phase of the inserted phase plate.

  2. Interference of single photon for input and output.
    Figure 2: Interference of single photon for input and output.

    a,b, Coincidence between the Stokes photon detected by detector D3 and the anti-Stokes photon detected by detector D1 (circles) and detector D2 (triangles), respectively, with a different phase before (a) and after (b) storage. Solid curves are fitted lines. All experimental data are raw data without error corrections. Error bars are ±1 standard deviation.

  3. Density matrices for input and output.
    Figure 3: Density matrices for input and output.

    a,b, Density matrices of the input state before storage (a) and the output state after storage (b). All experimental data are raw data without any error corrections.

  4. Reconstructed density matrix before and after storage.
    Figure 4: Reconstructed density matrix before and after storage.

    ad, Reconstructed real (a,c) and imaginary (b,d) parts of the input (a,b) and output (c,d) density matrices, respectively. The density matrices were reconstructed with losses. All experimental data are raw data without error corrections.

  5. Two-photon interference before and after storage.
    Figure 5: Two-photon interference before and after storage.

    The red and blue curves represent the coincidence rates for detectors D2 and D3, respectively, with the Stokes photons projected in the base: |H〉((|H〉 − |V〉)/21/2). a,b, Interference before (a) and after (b) storage. Data are all raw data without any corrections. Error bars are ±1 standard deviation.


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Author information

  1. These authors contributed equally to this work

    • Dong-Sheng Ding &
    • Wei Zhang


  1. Key Laboratory of Quantum Information, University of Science and Technology of China, Hefei, Anhui 230026, China

    • Dong-Sheng Ding,
    • Wei Zhang,
    • Zhi-Yuan Zhou,
    • Shuai Shi,
    • Bao-Sen Shi &
    • Guang-Can Guo
  2. Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China

    • Dong-Sheng Ding,
    • Wei Zhang,
    • Zhi-Yuan Zhou,
    • Shuai Shi,
    • Bao-Sen Shi &
    • Guang-Can Guo


B.S.S. conceived the idea and experiment. W.Z. and D.S.D. designed and carried out the experiments with assistance from Z.Y.Z. and S.S. D.S.D. and W.Z. carried out data analysis. D.S.D. wrote the manuscript. B.S.S. and G.C.G. supervised the project.

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The authors declare no competing financial interests.

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