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Coherence time of over a second in a telecom-compatible quantum memory storage material


Quantum memories for light will be essential elements in future long-range quantum communication networks. These memories operate by reversibly mapping the quantum state of light onto the quantum transitions of a material system. For networks, the quantum coherence times of these transitions must be long compared to the network transmission times, approximately 100 ms for a global communication network. Due to a lack of a suitable storage material, a quantum memory that operates in the 1,550 nm optical fibre communication band with a storage time greater than 1 μs has not been demonstrated. Here we describe the spin dynamics of 167Er3+: Y2SiO5 in a high magnetic field and demonstrate that this material has the characteristics for a practical quantum memory in the 1,550 nm communication band. We observe a hyperfine coherence time of 1.3 s. We also demonstrate efficient spin pumping of the entire ensemble into a single hyperfine state, a requirement for broadband spin-wave storage. With an absorption of 70 dB cm−1 at 1,538 nm and Λ transitions enabling spin-wave storage, this material is the first candidate identified for an efficient, broadband quantum memory at telecommunication wavelengths.

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Figure 1: 1,538 nm optical transition of 167Er3+: Y2SiO5.
Figure 2: Absorption spectrum of 167Er3+: Y2SiO5 with 95% of the ensemble pumped into the |+7/2〉 hyperfine spin state (orange, vertical axis on left), obtained by AM spectroscopy.
Figure 3: The decay rate of 167Er3+ nuclear spin polarization as a function of temperature, for a field of 7 T.
Figure 4: The lifetime of spectral holes burnt into the ΔmI = +1 absorption band of 167Er3+: Y2SiO5 at 1.4 K, as a function of magnetic field along the D1 axis.
Figure 5: Raman echo measurement of 167Er coherence time.


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M.J.S. would like to thank C. Thiel for insightful discussions. This work was supported by the Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology (Grant No. CE110001027). M.J.S. was supported by an Australian Research Council Future Fellowship (Grant No. FT110100919).

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M.J.S. and M.P.H. conceived the initial project. M.J.S., M.P.H. and M.R. designed the experimental set-up. M.R. carried out the experiment. M.R. and R.L.A. analysed the results. All authors contributed to writing the manuscript.

Corresponding author

Correspondence to Miloš Rančić.

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The authors declare no competing financial interests.

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Rančić, M., Hedges, M., Ahlefeldt, R. et al. Coherence time of over a second in a telecom-compatible quantum memory storage material. Nature Phys 14, 50–54 (2018).

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