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The speed of information in a ‘fast-light’ optical medium

Nature volume 425, pages 695–698 (2003)Cite this article

Abstract

One consequence of the special theory of relativity is that no signal can cause an effect outside the source light cone, the space-time surface on which light rays emanate from the source1. Violation of this principle of relativistic causality leads to paradoxes, such as that of an effect preceding its cause2. Recent experiments on optical pulse propagation in so-called ‘fast-light’ media—which are characterized by a wave group velocity υg exceeding the vacuum speed of light c or taking on negative values3—have led to renewed debate about the definition of the information velocity υi. One view is that υi = υg (ref. 4), which would violate causality, while another is that υi = c in all situations5, which would preserve causality. Here we find that the time to detect information propagating through a fast-light medium is slightly longer than the time required to detect the same information travelling through a vacuum, even though υg in the medium vastly exceeds c. Our observations are therefore consistent with relativistic causality and help to resolve the controversies surrounding superluminal pulse propagation.

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Figure 1: Fast-light pulse propagation.
Figure 2: Transmitting information-encoded optical pulses through a fast-light medium.
Figure 3: Detecting the arrival of new information.

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Acknowledgements

M.D.S. and D.J.G. acknowledge discussions with M. Gehm and J. Thomas, the loan of an argon-ion pump laser from J. Thomas, and the financial support of the US National Science Foundation.

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Authors and Affiliations

  1. Department of Physics, and The Fitzpatrick Center for Photonics and Communication Systems, Duke University, Durham, North Carolina, 27708, USA

    Michael D. Stenner & Daniel J. Gauthier

  2. Department of Electrical and Computer Engineering, The Optical Sciences Center, University of Arizona, Tucson, Arizona, 85721, USA

    Mark A. Neifeld

Authors
  1. Michael D. Stenner
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  2. Daniel J. Gauthier
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  3. Mark A. Neifeld
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Correspondence to Daniel J. Gauthier.

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Stenner, M., Gauthier, D. & Neifeld, M. The speed of information in a ‘fast-light’ optical medium. Nature 425, 695–698 (2003). https://doi.org/10.1038/nature02016

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