High-fidelity transfer and storage of photon states in a single nuclear spin

Journal name:
Nature Photonics
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Long-distance quantum communication requires photons and quantum nodes that comprise qubits for interaction with light and good memory capabilities, as well as processing qubits for the storage and manipulation of photons. Owing to the unavoidable photon losses, robust quantum communication over lossy transmission channels requires quantum repeater networks1, 2. A necessary and highly demanding prerequisite for these networks is the existence of quantum memories with long coherence times to reliably store the incident photon states. Here we demonstrate the high-fidelity (∼98%) coherent transfer of a photon polarization state to a single solid-state nuclear spin that has a coherence time of over 10 s. The storage process is achieved by coherently transferring the polarization state of a photon to an entangled electron–nuclear spin state of a nitrogen–vacancy centre in diamond. The nuclear spin-based optical quantum memory demonstrated here paves the way towards an absorption-based quantum repeater network.

At a glance


  1. Quantum interface connecting light to a single nuclear spin in an NV centre.
    Figure 1: Quantum interface connecting light to a single nuclear spin in an NV centre.

    ac, Schematic diagram and pulse scheme of transferring a photon polarization state to a nuclear spin in three steps: Bell state preparation of the electron–nuclear spin system (a), optical transfer (b) and heralding (c). a, The Bell state is prepared from the |0〉e|0〉n initial state by two control NOT gate operations. Blue arrows correspond to the electron spin-controlled NOT gate operation whereas green arrows correspond to the nuclear spin-controlled NOT gate operations. Intertwining blue curves represent entanglement between the electron and nuclear spins. Here the MW frequency is 2.879 GHz and RF0 is 4.946 MHz. b, A photon excites an electron to the A1 state and transfers its polarization information to the nuclear spin. Red and orange arrrows represent σ+ and σ polarization-selective transitions. c, The excited state |A1〉 relaxes to the ground state |0〉e with the photon polarization state stored into the nuclear spin (black arrows). This is heralded by detecting the electron spin in states |0〉e (three substates enclosed in the red dashed circle) through a single-shot readout, which is performed by a continuous excitation of the cycling transition between |0〉e and |Ex〉 and the detection of the emitted photons (red arrows). d, Circuit diagram and the pulse sequence for storing a photon into the nuclear spin and its subsequent verification. After heralding, the nuclear spin state is in .

  2. Nuclear spin readout.
    Figure 2: Nuclear spin readout.

    a,b, Deterministic initialization of the 14N nuclear spin. a, Energy-level diagram and pulse sequence describing the initialization of the 14N nuclear spin. The colours used for the various transitions involved are same as those in Fig. 1. b, Nuclear spin population measurements before (green) and after (red) nuclear initialization. The two different scales shown correspond to the different methods involved in the measurement procedure. To measure the nuclear spin population in its thermal state (green) we use the optically detected magnetic resonance of the electron spin, and to measure the nuclear spin population after initialization (red) we perform a single-shot readout of the electron spin state |0〉e. Here the MW frequency is 2.879 GHz and RF1 frequency is 2.76 MHz. Data in the red/green curves are accumulated for 600 and 2,000 rounds, respectively. Error bars indicate the shot-noise errors. c, nuclear spin state measurement after storing the photonic state . We measure the electron spin Rabi oscillation conditioned on the nuclear spin states (green) and (red), to obtain the nuclear spin state populations pb and pd. The transferred phase is then found from the simple equation, , which in the present case is zero. Data are accumulated for 350 rounds. d, Reconstructed density matrix of the nuclear spin from data in c. The shaded areas in the plots mark 95% confidence intervals.

  3. Full phase-space measurement.
    Figure 3: Full phase-space measurement.

    a, Population difference between the dark and bright state of the nuclear spin state (defined in Fig. 2) for different input phases of the optical photons, which shows the cosϕ oscillation as expected. b, Comparison between the phase of the nuclear spin and the phase of optical photons. Shaded areas in the plots mark 95% confidence intervals. Error bars indicate the errors from fitting.

  4. Coherence of the nuclear spin memory.
    Figure 4: Coherence of the nuclear spin memory.

    a, Nuclear spin Hahn measurements for spin coherence between state |0〉e|+1〉n and state |0〉e|−1〉n. Data are accumulated for 200 rounds. b, Nuclear spin Hahn measurements for spin coherence between state and state |±1〉e|0〉n. Data are accumulated for 900 rounds. The shaded areas in the plots mark the 95% confidence intervals and the error bars indicate the shot-noise errors.


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Author information

  1. These authors contributed equally to this work

    • Sen Yang &
    • Ya Wang


  1. 3. Physikalisches Institut and Research Center SCOPE, University of Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany

    • Sen Yang,
    • Ya Wang,
    • D. D. Bhaktavatsala Rao,
    • Thai Hien Tran,
    • Ali S. Momenzadeh,
    • Rainer Stöhr,
    • Philipp Neumann &
    • Jörg Wrachtrup
  2. Max Planck Institute for Solid State Research, Heisenbergstraße, 1 70569 Stuttgart, Germany

    • D. D. Bhaktavatsala Rao &
    • Jörg Wrachtrup
  3. Global Innovation Centre, Element Six Ltd, Fermi Avenue, Harwell Oxford, Didcot, Oxfordshire OX11 0QR, UK

    • M. Markham
  4. Element Six Technologies US Corporation, 3901 Burton Drive, Santa Clara, California 95054, USA

    • D. J. Twitchen
  5. Beijing Computational Science Research Center, Beijing 100084, China

    • Ping Wang &
    • Wen Yang
  6. Institute for Quantum Computing, University of Waterloo, Waterloo N2L 3G1, Canada

    • Rainer Stöhr
  7. Department of Physics, Faculty of Engineering, Yokohama National University, Tokiwadai, Hodogayaku, Yokohama 240-8501, Japan

    • Hideo Kosaka


H.K. conceived the original idea, S.Y., Y.W. and P.N. designed the experiment, S.Y. and T.H.T. performed the experiment, S.Y., Y.W. and D.D.B. analysed data and wrote the paper, J.W. supervised the project and all authors commented on the manuscript.

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The authors declare no competing financial interests.

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