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Observation of entanglement between a quantum dot spin and a single photon


Entanglement has a central role in fundamental tests of quantum mechanics1 as well as in the burgeoning field of quantum information processing. Particularly in the context of quantum networks and communication, a main challenge is the efficient generation of entanglement between stationary (spin) and propagating (photon) quantum bits2. Here we report the observation of quantum entanglement between a semiconductor quantum dot spin and the colour of a propagating optical photon. The demonstration of entanglement relies on the use of fast, single-photon detection, which allows us to project the photon into a superposition of red and blue frequency components. Our results extend the previous demonstrations of single-spin/single-photon entanglement in trapped ions3, neutral atoms4,5 and nitrogen–vacancy centres6 to the domain of artificial atoms in semiconductor nanostructures that allow for on-chip integration of electronic and photonic elements7,8. As a result of its fast optical transitions and favourable selection rules, the scheme we implement could in principle generate nearly deterministic entangled spin–photon pairs at a rate determined ultimately by the high spontaneous emission rate. Our observation constitutes a first step towards implementation of a quantum network with nodes9 consisting of semiconductor spin quantum bits10,11,12.

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Figure 1: Quantum dot transitions and experimental set-up.
Figure 2: Measurement of classical spin–photon correlations.
Figure 3: Demonstration of quantum correlation between the electron spin and the emitted single-photon pulse.


  1. Aspect, A., Grangier, P. & Roger, G. Experimental realization of Einstein-Podolsky-Rosen-Bohm gedanken experiment: a new violation of Bell’s inequalities. Phys. Rev. Lett. 49, 91–94 (1982)

    Article  ADS  Google Scholar 

  2. DiVincenzo, D. P. The physical implementation of quantum computation. Fortschr. Phys. 48, 771–783 (2000)

    Article  Google Scholar 

  3. Blinov, B., Moehring, D. & Duan, L. Observation of entanglement between a single trapped atom and a single photon. Nature 428, 153–157 (2004)

    Article  ADS  CAS  Google Scholar 

  4. Volz, J. et al. Observation of entanglement of a single photon with a trapped atom. Phys. Rev. Lett. 96, 030404 (2006)

    Article  ADS  Google Scholar 

  5. Wilk, T., Webster, S. C., Kuhn, A. & Rempe, G. Single-atom single-photon quantum interface. Science 317, 488–490 (2007)

    Article  ADS  CAS  Google Scholar 

  6. Togan, E. et al. Quantum entanglement between an optical photon and a solid-state spin qubit. Nature 466, 730–734 (2010)

    Article  ADS  CAS  Google Scholar 

  7. Hennessy, K. et al. Quantum nature of a strongly coupled single quantum dot-cavity system. Nature 445, 896–899 (2007)

    Article  ADS  CAS  Google Scholar 

  8. Faraon, A. et al. Coupling of nitrogen-vacancy centers to photonic crystal cavities in monocrystalline diamond. Phys. Rev. Lett 109, 033604 (2012)

    Article  ADS  Google Scholar 

  9. Yuan, Z.-S. et al. Experimental demonstration of a BDCZ quantum repeater node. Nature 454, 1098–1101 (2008)

    Article  ADS  CAS  Google Scholar 

  10. Loss, D. & DiVincenzo, D. P. Quantum computation with quantum dots. Phys. Rev. A 57, 120–126 (1998)

    Article  ADS  CAS  Google Scholar 

  11. Imamoğlu, A. et al. Quantum information processing using quantum dot spins and cavity QED. Phys. Rev. Lett. 83, 4204–4207 (1999)

    Article  ADS  Google Scholar 

  12. Hanson, R. et al. Spins in few-electron quantum dots. Rev. Mod. Phys. 79, 1217–1265 (2007)

    Article  ADS  CAS  Google Scholar 

  13. Press, D., Ladd, T. D., Zhang, B. & Yamamoto, Y. Complete quantum control of a single quantum dot spin using ultrafast optical pulses. Nature 456, 218–221 (2008)

    Article  ADS  CAS  Google Scholar 

  14. Greilich, A. et al. Ultrafast optical rotations of electron spins in quantum dots. Nature Phys. 5, 262–266 (2009)

    Article  ADS  CAS  Google Scholar 

  15. Poem, E. et al. Accessing the dark exciton with light. Nature Phys. 6, 993–997 (2010)

    Article  ADS  CAS  Google Scholar 

  16. Kim, D. et al. Ultrafast optical control of entanglement between two quantum-dot spins. Nature Phys. 7, 223–229 (2011)

    Article  ADS  CAS  Google Scholar 

  17. Shulman, M. D. et al. Demonstration of entanglement of electrostatically coupled singlet-triplet qubits. Science 336, 202–205 (2012)

    Article  ADS  CAS  Google Scholar 

  18. Cirac, J., Ekert, A. & Huelga, S. Distributed quantum computation over noisy channels. Phys. Rev. A 59, 4249–4254 (1999)

    Article  ADS  MathSciNet  CAS  Google Scholar 

  19. Xu, X. et al. Fast spin state initialization in a singly charged InAs-GaAs quantum dot by optical cooling. Phys. Rev. Lett. 99, 097401 (2007)

    Article  ADS  Google Scholar 

  20. Muller, A. et al. Resonance fluorescence from a coherently driven semiconductor quantum dot in a cavity. Phys. Rev. Lett. 99, 187402 (2007)

    Article  ADS  CAS  Google Scholar 

  21. Vamivakas, A. N., Zhao, Y., Lu, C.-Y. & Atature, M. Spin-resolved quantum-dot resonance fluorescence. Nature Phys. 5, 198–202 (2009); corrigendum. 5, 925 (2009)

    Article  ADS  Google Scholar 

  22. Yılmaz, S. T., Fallahi, P. & Imamoglu, A. Quantum-dot-spin single-photon interface. Phys. Rev. Lett. 105, 033601 (2010)

    Article  ADS  Google Scholar 

  23. Gol’tsman, G. N. et al. Picosecond superconducting single-photon detector. Appl. Phys. Lett. 79, 705–707 (2001)

    Article  ADS  Google Scholar 

  24. Press, D. et al. Ultrafast optical spin echo in a single quantum dot. Nature Photon. 4, 367–370 (2010)

    Article  ADS  CAS  Google Scholar 

  25. Claudon, J. et al. A highly efficient single-photon source based on a quantum dot in a photonic nanowire. Nature Photon. 4, 174–177 (2010)

    Article  ADS  CAS  Google Scholar 

  26. Dousse, A. et al. Ultrabright source of entangled photon pairs. Nature 466, 217–220 (2010)

    Article  ADS  CAS  Google Scholar 

  27. Xu, X. et al. Optically controlled locking of the nuclear field via coherent dark-state spectroscopy. Nature 459, 1105–1109 (2009)

    Article  ADS  CAS  Google Scholar 

  28. Flagg, E. B. et al. Interference of single photons from two separate semiconductor quantum dots. Phys. Rev. Lett. 104, 137401 (2010)

    Article  ADS  Google Scholar 

  29. Patel, R. et al. Two-photon interference of the emission from electrically tunable remote quantum dots. Nature Photon. 4, 632–635 (2010)

    Article  ADS  CAS  Google Scholar 

  30. Moehring, D. L. et al. Entanglement of single-atom quantum bits at a distance. Nature 449, 68–71 (2007)

    Article  ADS  CAS  Google Scholar 

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We acknowledge discussions with W. Chin, M. Kroner, A. Srivastava, J. Elzerman, A. Reinhard, T. Volz, P. Maletinsky and D. Gershoni. This work is supported by NCCR Quantum Science and Technology, a research instrument of the Swiss National Science Foundation; the Swiss NSF (grant no. 200021-140818); an ERC Advanced Investigator Grant (A.I.); and a Marie Curie International Incoming Fellowship within FP7 (W.B.G.).

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Correspondence to W. B. Gao or A. Imamoglu.

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Gao, W., Fallahi, P., Togan, E. et al. Observation of entanglement between a quantum dot spin and a single photon. Nature 491, 426–430 (2012).

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