The faithful storage of a quantum bit (qubit) of light is essential for long-distance quantum communication, quantum networking and distributed quantum computing1. The required optical quantum memory must be able to receive and recreate the photonic qubit; additionally, it must store an unknown quantum state of light better than any classical device. So far, these two requirements have been met only by ensembles of material particles that store the information in collective excitations2,3,4,5,6,7. Recent developments, however, have paved the way for an approach in which the information exchange occurs between single quanta of light and matter8,9,10,11,12,13. This single-particle approach allows the material qubit to be addressed, which has fundamental advantages for realistic implementations. First, it enables a heralding mechanism that signals the successful storage of a photon by means of state detection14,15,16; this can be used to combat inevitable losses and finite efficiencies. Second, it allows for individual qubit manipulations, opening up avenues for in situ processing of the stored quantum information. Here we demonstrate the most fundamental implementation of such a quantum memory, by mapping arbitrary polarization states of light into and out of a single atom trapped inside an optical cavity. The memory performance is tested with weak coherent pulses and analysed using full quantum process tomography. The average fidelity is measured to be 93%, and low decoherence rates result in qubit coherence times exceeding 180 microseconds. This makes our system a versatile quantum node with excellent prospects for applications in optical quantum gates17 and quantum repeaters18.
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Lvovsky, A. I., Sanders, B. C. & Tittel, W. Optical quantum memory. Nature Photon. 3, 706–714 (2009)
Matsukevich, D. N. et al. Entanglement of remote atomic qubits. Phys. Rev. Lett. 96, 030405 (2006)
Choi, K. S., Deng, H., Laurat, J. & Kimble, H. J. Mapping photonic entanglement into and out of a quantum memory. Nature 452, 67–71 (2008)
Tanji, H., Ghosh, S., Simon, J., Bloom, B. & Vuletic´, V. Heralded single-magnon quantum memory for photon polarization states. Phys. Rev. Lett. 103, 043601 (2009)
Jin, X.-M. et al. Quantum interface between frequency-uncorrelated down-converted entanglement and atomic-ensemble quantum memory. Preprint at 〈http://arxiv.org/abs/1004.4691〉 (2010)
Saglamyurek, E. et al. Broadband waveguide quantum memory for entangled photons. Nature 469, 512–515 (2011)
Clausen, C. et al. Quantum storage of photonic entanglement in a crystal. Nature 469, 508–511 (2011)
Cirac, J. I., Zoller, P., Kimble, H. J. & Mabuchi, H. Quantum state transfer and entanglement distribution among distant nodes in a quantum network. Phys. Rev. Lett. 78, 3221–3224 (1997)
Blinov, B. B., Moehring, D. L., Duan, L.-M. & Monroe, C. Observation of entanglement between a single trapped atom and a single photon. Nature 428, 153–157 (2004)
Volz, J. et al. Observation of entanglement of a single photon with a trapped atom. Phys. Rev. Lett. 96, 030404 (2006)
Wilk, T., Webster, S. C., Kuhn, A. & Rempe, G. Single-atom single-photon quantum interface. Science 317, 488–490 (2007)
Boozer, A. D., Boca, A., Miller, R., Northup, T. E. & Kimble, H. J. Reversible state transfer between light and a single trapped atom. Phys. Rev. Lett. 98, 193601 (2007)
Togan, E. et al. Quantum entanglement between an optical photon and a solid-state spin qubit. Nature 466, 730–734 (2010)
Lloyd, S., Shahriar, M. S., Shapiro, J. H. & Hemmer, P. R. Long distance, unconditional teleportation of atomic states via complete Bell state measurements. Phys. Rev. Lett. 87, 167903 (2001)
Bochmann, J. et al. Lossless state detection of single neutral atoms. Phys. Rev. Lett. 104, 203601 (2010)
Piro, N. et al. Heralded single-photon absorption by a single atom. Nature Phys. 7, 17–20 (2011)
Jaksch, D. et al. Fast quantum gates for neutral atoms. Phys. Rev. Lett. 85, 2208–2211 (2000)
Briegel, H.-J., Dür, W., Cirac, J. I. & Zoller, P. Quantum repeaters: the role of imperfect local operations in quantum communication. Phys. Rev. Lett. 81, 5932–5935 (1998)
Mücke, M. et al. Electromagnetically induced transparency with single atoms in a cavity. Nature 465, 755–758 (2010)
Kampschulte, T. et al. Optical control of the refractive index of a single atom. Phys. Rev. Lett. 105, 153603 (2010)
Hennrich, M., Legero, T., Kuhn, A. & Rempe, G. Vacuum-stimulated Raman scattering based on adiabatic passage in a high-finesse optical cavity. Phys. Rev. Lett. 85, 4872–4875 (2000)
Keller, M., Lange, B., Hayasaka, K., Lange, W. & Walther, H. Continuous generation of single photons with controlled waveform in an ion-trap cavity system. Nature 431, 1075–1078 (2004)
Vasilev, G. S., Ljunggren, D. & Kuhn, A. Single photons made-to-measure. N. J. Phys. 12, 063024 (2010)
Gorshkov, A. V., André, A., Lukin, M. D. & Sørensen, A. S. Photon storage in Λ-type optically dense atomic media. I. Cavity model. Phys. Rev. A 76, 033804 (2007)
James, D. F. V., Kwiat, P. G., Munro, W. J. & White, A. G. Measurement of qubits. Phys. Rev. A 64, 052312 (2001)
Bowdrey, M. D., Oi, D. K. L., Short, A., Banaszek, K. & Jones, J. Fidelity of single qubit maps. Phys. Lett. A 294, 258–260 (2002)
Curty, M. & Lütkenhaus, N. Intercept-resend attacks in the Bennett-Brassard 1984 quantum-key-distribution protocol with weak coherent pulses. Phys. Rev. A 71, 062301 (2005)
Massar, S. & Popescu, S. Optimal extraction of information from finite quantum ensembles. Phys. Rev. Lett. 74, 1259–1263 (1995)
Nielsen, M. A. & Chuang, I. L. Quantum Computation and Quantum Information (Cambridge Univ. Press, 2000)
Zhao, B. et al. A millisecond quantum memory for scalable quantum networks. Nature Phys. 5, 95–99 (2009)
Zhao, R. et al. Long-lived quantum memory. Nature Phys. 5, 100–104 (2009)
Radnaev, A. G. et al. A quantum memory with telecom-wavelength conversion. Nature Phys. 6, 894–899 (2010)
We thank N. Kiesel for discussions and A. Neuzner for experimental assistance. This work was supported by the Deutsche Forschungsgemeinschaft (Research Unit 635), by the European Union (Collaborative Project AQUTE) and by the Bundesministerium für Bildung und Forschung via IKT 2020 (QK_QuOReP). E.F. acknowledges support from the Alexander von Humboldt Foundation.
The authors declare no competing financial interests.
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Specht, H., Nölleke, C., Reiserer, A. et al. A single-atom quantum memory. Nature 473, 190–193 (2011). https://doi.org/10.1038/nature09997
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