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# Quantum nature of a strongly coupled single quantum dot–cavity system

## Abstract

Cavity quantum electrodynamics (QED) studies the interaction between a quantum emitter and a single radiation-field mode. When an atom is strongly coupled to a cavity mode1,2, it is possible to realize important quantum information processing tasks, such as controlled coherent coupling and entanglement of distinguishable quantum systems. Realizing these tasks in the solid state is clearly desirable, and coupling semiconductor self-assembled quantum dots to monolithic optical cavities is a promising route to this end. However, validating the efficacy of quantum dots in quantum information applications requires confirmation of the quantum nature of the quantum-dot–cavity system in the strong-coupling regime. Here we find such confirmation by observing quantum correlations in photoluminescence from a photonic crystal nanocavity3,4,5 interacting with one, and only one, quantum dot located precisely at the cavity electric field maximum. When off-resonance, photon emission from the cavity mode and quantum-dot excitons is anticorrelated at the level of single quanta, proving that the mode is driven solely by the quantum dot despite an energy mismatch between cavity and excitons. When tuned to resonance, the exciton and cavity enter the strong-coupling regime of cavity QED and the quantum-dot exciton lifetime reduces by a factor of 145. The generated photon stream becomes antibunched, proving that the strongly coupled exciton/photon system is in the quantum regime. Our observations unequivocally show that quantum information tasks are achievable in solid-state cavity QED.

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## References

1. Mabuchi, H. & Doherty, A. C. Cavity quantum electrodynamics: Coherence in context. Science 298, 1372–1377 (2002)

2. Raimond, J. M., Brune, M. & Haroche, S. Colloquium: Manipulating quantum entanglement with atoms and photons in a cavity. Rev. Mod. Phys. 73, 565–582 (2001)

3. Painter, O. et al. Two-dimensional photonic band-gap defect mode laser. Science 284, 1819–1821 (1999)

4. Strauf, S. et al. Self-tuned quantum dot gain in photonic crystal lasers. Phys. Rev. Lett. 96, 127404 (2006)

5. Akahane, Y., Asano, T., Song, B. S. & Noda, S. High-Q photonic nanocavity in a two-dimensional photonic crystal. Nature 425, 944–947 (2003)

6. Wallraff, A. et al. Strong coupling of a single photon to a superconducting qubit using circuit quantum electrodynamics. Nature 431, 162–167 (2004)

7. Peter, E. et al. Exciton-photon strong-coupling regime for a single quantum dot embedded in a microcavity. Phys. Rev. Lett. 95, 067401 (2005)

8. Yoshie, T. et al. Vacuum Rabi splitting with a single quantum dot in a photonic crystal nanocavity. Nature 432, 200–203 (2004)

9. Reithmaier, J. P. et al. Strong coupling in a single quantum dot-semiconductor microcavity system. Nature 432, 197–200 (2004)

10. Badolato, A. et al. Deterministic coupling of single quantum dots to single nanocavity modes. Science 308, 1158–1161 (2005)

11. Hennessy, K., Badolato, A., Petroff, P. M. & Hu, E. L. Positioning photonic crystal cavities to single InAs quantum dots. Photonics Nanostruct. Fund. Applic. 2, 65–72 (2004)

12. Strauf, S. et al. Frequency control of photonic crystal membrane resonators by monolayer deposition. Appl. Phys. Lett. 88, 043116 (2006)

13. Kiraz, A. et al. Photon correlation spectroscopy of a single quantum dot. Phys. Rev. B 65, 161303 (2002)

14. Childs, J. J., An, K., Otteson, M. S., Dasari, R. R. & Feld, M. S. Normal mode line shapes for atoms in standing-wave optical resonators. Phys. Rev. Lett. 77, 2901–2904 (1996)

15. Yablonovitch, E. Inhibited spontaneous emission in solid-state physics and electronics. Phys. Rev. Lett. 58, 2059–2062 (1987)

16. Purcell, E. M. Spontaneous emission probabilities at radio frequencies. Phys. Rev. 69, 681 (1946)

17. Englund, D. et al. Controlling the spontaneous emission rate of single quantum dots in a two-dimensional photonic crystal. Phys. Rev. Lett. 95, 013904 (2005)

18. Andreani, L. C., Panzarini, G. & Gerard, J. M. Strong-coupling regime for quantum boxes in pillar microcavities: Theory. Phys. Rev. B 60, 13276–13279 (1999)

19. Pau, S., Bjork, G., Jacobson, J., Cao, H. & Yamamoto, Y. Microcavity exciton-polariton splitting in the linear regime. Phys. Rev. B 51, 14437–14447 (1995)

20. Haroche, S. Fundamental Systems in Quantum Optics (Elsevier, New York, 1992)

21. Brune, M. et al. Quantum Rabi oscillation: A direct test of field quantization in a cavity. Phys. Rev. Lett. 76, 1800–1803 (1996)

22. Birnbaum, K. M. et al. Photon blockade in an optical cavity with one trapped atom. Nature 436, 87–90 (2005)

23. Imamoglu, A., Schmidt, H., Woods, G. & Deutsch, M. Strongly interacting photons in a nonlinear cavity. Phys. Rev. Lett. 79, 1467–1470 (1997)

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

## Acknowledgements

We acknowledge support by the Swiss National Research Foundation through the ‘Quantum Photonics NCCR’.

## Author information

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Correspondence to A. Imamoğlu.

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Reprints and permissions information is available at www.nature.com/reprints. The authors declare no competing financial interests.

## Supplementary information

### Supplementary figures

This file contains Supplementary figures S1-S2 with legends. (PDF 358 kb)

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Hennessy, K., Badolato, A., Winger, M. et al. Quantum nature of a strongly coupled single quantum dot–cavity system. Nature 445, 896–899 (2007). https://doi.org/10.1038/nature05586

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• DOI: https://doi.org/10.1038/nature05586

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