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Gain-assisted superluminal light propagation

Nature volume406,pages277–279 (2000)Cite this article

ACorrigendumto this article was published on 21 June 2001

Abstract

Einstein's theory of special relativity and the principle of causality1,2,3,4imply that the speed of any moving object cannot exceed that of light in a vacuum (c). Nevertheless, there exist various proposals5,6,7,8,9,10,11,12,13,14,15,16,17,18for observing faster-than-cpropagation of light pulses, using anomalous dispersion near an absorption line4,6,7,8,nonlinear9and linear gain lines10,11,12,13,14,15,16,17,18,or tunnelling barriers19.However, in all previous experimental demonstrations, the light pulses experienced either very large absorption7or severe reshaping9,19,resulting in controversies over the interpretation. Here we use gain-assisted linear anomalous dispersion to demonstrate superluminal light propagation in atomic caesium gas. The group velocity of a laser pulse in this region exceedscand can even become negative16,17,while the shape of the pulse is preserved. We measure a group-velocity index ofng= -310(±5); in practice, this means that a light pulse propagating through the atomic vapour cell appears at the exit side so much earlier than if it had propagated the same distance in a vacuum that the peak of the pulse appears to leave the cell before entering it. The observed superluminal light pulse propagation is not at odds with causality, being a direct consequence of classical interference between its different frequency components in an anomalous dispersion region.

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Figure 1: Gain-assisted anomalous dispersion.
Figure 2: Schematic experimental set-up.
Figure 3: Measured refractive index and gain coefficient.
Figure 4: Measured pulse advancement for a light pulse traversing through the caesium vapour in the gain-assisted superluminality state.

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References

  1. Einstein, A., Lorentz, H. A., Minkowski, H. & Weyl, H.The Principle of Relativity, Collected Papers(Dover, New York, 1952).

    MATH Google Scholar

  2. Born, M. & Wolf, E.Principle of Optics7th edn (Cambridge Univ. Press, Cambridge, 1997).

    Google Scholar

  3. Landau, L. D. & Lifshitz, E. M.Electrodynamics of Continuous Media(Pergamon, Oxford, 1960).

    MATH Google Scholar

  4. Brillouin, L.Wave Propagation and Group Velocity(Academic, New York, 1960).

    MATH Google Scholar

  5. Chiao, R. Y. inAmazing Light, a Volume Dedicated to C. H. Townes on His Eightieth Birthday(ed. Chiao, R. Y.) 91–108 (Springer, New York, 1996).

    Google Scholar

  6. Garrett, C. G. B. & McCumber, D. E. Propagation of a gaussian light pulse through an anomalous dispersion medium.Phys. Rev. A1,305–313 (1970).

    Article ADS Google Scholar

  7. Chu, S. & Wong, S. Linear pulse propagation in an absorbing medium.Phys. Rev. Lett.48,738– 741 (1982).

    Article ADS CAS Google Scholar

  8. Akulshin, A. M., Barreiro, S. & Lezama, A. Steep anomalous dispersion in coherently prepared Rb vapor.Phys. Rev. Lett.83,4277– 4280 (1999).

    Article ADS CAS Google Scholar

  9. Basov, N. G., Ambartsumyan, R. V., Zuev, V. S., Kryukov, P. G. & Letokhov, V. S. Nonlinear amplification of light pulses.Sov. Phys. JETP23,16– 22 (1966).

    ADS Google Scholar

  10. Casperson, L. & Yariv, A. Pulse propagation in a high-gain medium.Phys. Rev. Lett.26,293– 295 (1971).

    Article ADS Google Scholar

  11. Icsevgi, A. & Lamb, W. E. Propagation of light pulses in a laser amplifier.Phys. Rev.185,517– 545 (1969).

    Article ADS MathSciNet CAS Google Scholar

  12. Picholle, E., Montes, C., Leycuras, C., Legrand, O. & Botineau, J. Observation of dissipative superluminous solitons in a Brillouin fiber ring laser.Phys. Rev. Lett.66,1454–1457 (1991).

    Article ADS CAS Google Scholar

  13. Fisher, D. L. & Tajima, T. Superluminous laser pulse in an active medium.Phys. Rev. Lett.71,4338– 4341 (1993).

    Article ADS CAS Google Scholar

  14. Chiao, R. Y. Superluminal (but causal) propagation of wave packets in transparent media with inverted atomic populations.Phys. Rev. A48,R34–R37 (1993).

    Article ADS CAS Google Scholar

  15. Bolda, E. L., Chiao, R. Y. & Garrison, J. C. Two theorems for the group velocity in dispersive media.Phys. Rev. A48,3890– 3894 (1993).

    Article ADS CAS Google Scholar

  16. Steinberg, A. M. & Chiao, R. Y. Dispersionless, highly superluminal propagation in a medium with a gain doublet.Phys. Rev. A49,2071–2075 (1994).

    Article ADS CAS Google Scholar

  17. Mitchell, M. W. & Chiao, R. Y. Causality and negative group delays in a simple bandpass amplifier.Am. J. Phys.66,14–19 ( 1998).

    Article ADS Google Scholar

  18. Bolda, E., Garrison, J. C. & Chiao, R. Y. Optical pulse propagation at negative group velocities due to a nearby gain line.Phys. Rev. A49,2938–2947 (1994).

    Article ADS CAS Google Scholar

  19. Steinberg, A. M., Kwiat, P. G. & Chiao, R. Y. Measurement of the single-photon tunneling time.Phys. Rev. Lett.71,708– 711 (1993).

    Article ADS CAS Google Scholar

  20. Harris, S. E. Electromagnetically induced transparency.Phys. Today50,36–42 (1997).

    Article CAS Google Scholar

  21. Scully, M. O. & Zubairy, M. S.Quantum Optics(Cambridge Univ. Press, 1997).

    Book Google Scholar

  22. Xiao, M., Li, Y.-Q., Jin, S.-Z. & Gea-Banacloche, J. Measurement of dispersion properties of electromagnetically induced transparency in rubidium atoms.Phys. Rev. Lett.74,666– 669 (1995).

    Article ADS CAS Google Scholar

  23. Hau, L. V., Harris, S. E., Dutton, Z. & Behroozi, C. H. Light speed reduction to 17 meters per second in an untracold atomic gas.Nature397,594–598 (1999).

    Article ADS CAS Google Scholar

  24. Kash, M. M.et al.Ultraslow group velocity and enhanced nonlinear optical effects in a coherently driven hot atomic gas.Phys. Rev. Lett.82,5229–5232 (1999).

    Article ADS CAS Google Scholar

  25. Budker, D., Kimball, D. F., Rochester, S. M. & Yashchuk, V. V. Nonlinear magneto-optics and reduced group velocity of light in atomic vapor with slow ground state relaxation.Phys. Rev. Lett.83,1767–1770 (1999).

    Article ADS CAS Google Scholar

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Acknowledgements

We thank R. A. Linke for several stimulating discussions. We thank D. K. Walter, W. Happer, J. A. Giordmaine, D. J. Chadi, S. A. Solin, R. Y. Chiao, S. E. Harris and E. S. Polzik for helpful discussions. We thank E. B. Alexandrov and N. P. Bigelow for the use of the paraffin-coated caesium cells.

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  1. NEC Research Institute, 4 Independence Way, Princeton, 08540, New Jersey, USA

    L. J. Wang, A. Kuzmich & A. Dogariu

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  1. L. J. Wang
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Correspondence to L. J. Wang.

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Wang, L., Kuzmich, A. & Dogariu, A. Gain-assisted superluminal light propagation. Nature406,277–279 (2000). https://doi.org/10.1038/35018520

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