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Towards high-speed optical quantum memories


Quantum memories, capable of controllably storing and releasing a photon, are a crucial component for quantum computers1 and quantum communications2. To date, quantum memories3,4,5,6 have operated with bandwidths that limit data rates to megahertz. Here we report the coherent storage and retrieval of sub-nanosecond low-intensity light pulses with spectral bandwidths exceeding 1 GHz in caesium vapour. The novel memory interaction takes place through a far off-resonant two-photon transition in which the memory bandwidth is dynamically generated by a strong control field7,8. This should allow data rates more than 100 times greater than those of existing quantum memories. The memory works with a total efficiency of 15%, and its coherence is demonstrated through direct interference of the stored and retrieved pulses. Coherence times in hot atomic vapours are on the order of microseconds9, the expected storage time limit for this memory.

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Figure 1: Raman memory.
Figure 2: Experimental data for storage and retrieval processes.
Figure 3: Dependence of memory efficiency on write/read pulse energy.
Figure 4: Raw interference of stored and retrieved signals.
Figure 5: Experimental set-up.


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We thank D. Stacey, P. Walther and M.G. Raymer for useful discussions. This work was supported by the Engineering and Physical Sciences Research Council of the UK through the QIP IRC (Quantum Information Processing Interdisciplinary Research Collaboration: GR/S82716/01) and project EP/C51933/01. K.F.R. and V.O.L. were supported by the Marie-Curie-Network EMALI (Engineering, Manipulation and Characterization of Quantum States of Matter and Light). B.J.S. gratefully acknowledges support from the Natural Sciences and Engineering Research Council of Canada and from the Royal Society. I.A.W. was supported in part by the European Commission under the Integrated Project Qubit Applications (QAP) funded by the Information Society Technologies directorate as contract no. 015848, and the Royal Society.

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K.F.R. built the experiment, with initial assistance from V.O.L., and collected the data. K.F.R., J.N. and B.J.S. contributed to the theoretical analysis. N.K.L. assisted with design and analysis of the coherence measurements. K.C.L., N.K.L. and D.J. added useful insights, and I.A.W. conceived the experiment. The manuscript was written by K.F.R. with input from B.J.S., J.N., N.K.L. and I.A.W.

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Correspondence to I. A. Walmsley.

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The authors declare no competing financial interests.

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Reim, K., Nunn, J., Lorenz, V. et al. Towards high-speed optical quantum memories. Nature Photon 4, 218–221 (2010).

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