Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Letter
  • Published:

Gain without inversion in semiconductor nanostructures

Abstract

When Einstein showed that light amplification needed a collection of atoms in ‘population inversion’ (that is, where more than half the atoms are in an excited state, ready to emit light rather than absorb it) he was using thermodynamic arguments1. Later on, quantum theory predicted2,3 that matter–wave interference effects inside the atoms could, in principle, allow gain without inversion (GWI). The coherent conditions needed to observe this strange effect have been generated in atomic vapours4, but here we show that semiconductor nanostructures can be tailored to have ‘artificial atom’ electron states which, for the first time in a solid, also show GWI. In atomic experiments, the coherent conditions, typically generated either by coupling two electron levels to a third with a strong light beam2,3 or by tunnel coupling both levels to the same continuum (Fano effect5), are also responsible for the observation of ‘electromagnetically induced transparency’ (EIT)6. In turn, this has allowed observations of markedly slowed7 and even frozen8 light propagation. Our ‘artificial atom’ GWI effects are rooted in the same phenomena and, from an analysis of the absorption changes, we infer that the light slows to c/40 over the spectral range where the optical gain appears.

This is a preview of subscription content, access via your institution

Access options

Buy this article

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Schematic of the ‘dressing’ of electron energy levels by a strong coupling beam9.
Figure 2: The ‘artificial atom’ layered semiconductor nanostructure and the prism-shaped sample.
Figure 3: Optical absorption/gain spectra for the |1〉–|2〉 transition in the presence of various coupling fields.
Figure 4: Dispersion characteristics in the region of the GWI feature.

Similar content being viewed by others

References

  1. Einstein, A. The quantum theory of radiation. Phys. Z. 18, 121–128 (1917).

    Google Scholar 

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

    Book  Google Scholar 

  3. Mandel, L. & Wolf, E. Optical Coherence and Quantum Optics (Cambridge Univ. Press, Cambridge, 1995).

    Book  Google Scholar 

  4. Mompart, J. & Corbalan, R. Lasing without inversion. J. Opt. B 2, R7–R24 (2000).

    Article  Google Scholar 

  5. Harris, S. E. Lasers without inversion: Interference of lifetime broadened resonances. Phys. Rev. Lett. 62, 1033–1036 (1989).

    Article  Google Scholar 

  6. Boller, K.-J., Imamoǧlu, A. & Harris, S. E. Observation of electromagnetically induced transparency. Phys. Rev. Lett. 66, 2954–2956 (1991).

    Article  Google Scholar 

  7. Hau, L. W., Harris, S. E., Dutton, Z. & Behroozi, C. H. Light speed reduction to 17 metres per second in an ultracold atomic gas. Nature 397, 594–598 (1999).

    Article  Google Scholar 

  8. Bajcsy, M., Zibrov, A. S. & Lukin, M. D. Stationary pulses of light in an atomic medium. Nature 426, 638–641 (2003).

    Article  Google Scholar 

  9. Berman, P. R. & Salomaa, R. Comparison between dressed-atom and bare-atom pictures in laser spectroscopy. Phys. Rev. A 25, 2667–2692 (1982).

    Article  Google Scholar 

  10. Wu, F. Y., Ezekiel, E., Ducloy, M. & Mollow, B. R. Observation of amplification in a strongly driven two-level atomic system at optical frequencies. Phys. Rev. Lett. 38, 1077–1080 (1977).

    Article  Google Scholar 

  11. Luo, C. W. et al. Phase resolved non-linear response of a two dimensional electron gas under femtosecond intersubband excitation. Phys. Rev. Lett. 92, 047402 (2004).

    Article  Google Scholar 

  12. Dynes, J. F., Frogley, M. D., Beck, M., Faist, J. & Phillips, C. C. AC stark splitting and quantum interference with intersubband transitions in quantum wells. Phys. Rev. Lett. 94, 157403 (2005).

    Article  Google Scholar 

  13. Turukhin, A. V. et al. Observation of ultraslow and stored light pulses in a solid. Phys. Rev. Lett. 88, 023602 (2002).

    Article  Google Scholar 

  14. Bigelow, M. S., Lepeshkin, N. N. & Boyd, R. W. Superluminal and slow light propagation in a room-temperature solid. Science 301, 200–202 (2003).

    Article  Google Scholar 

  15. Bigelow, M. S., Lepeshkin, N. N. & Boyd, R. W. Observation of ultraslow light propagation in ruby crystals at room temperature. Phys. Rev. Lett. 90, 113903 (2003).

    Article  Google Scholar 

  16. Schültzgen, A. et al. Direct observation of excitonic Rabi oscillations in semiconductors. Phys. Rev. Lett. 82, 2346–2349 (1999).

    Article  Google Scholar 

  17. Shimano, R. & Kuwata-Gonokami, M. Observation of Autler-Townes splitting of biexcitons in CuCl. Phys. Rev. Lett. 72, 530–533 (1994).

    Article  Google Scholar 

  18. Faist, J., Capasso, F., Sirtori, C., West, K. W. & Pfeiffer, L. N. Controlling the sign of quantum interference by tunnelling from quantum wells. Nature 390, 589–591 (1997).

    Article  Google Scholar 

  19. Serapiglia, G. B., Paspalakis, E., Sirtori, C., Vodopyanov, K. L. & Phillips, C. C. Observation of laser-induced quantum coherence in a semiconductor quantum well. Phys. Rev. Lett. 84, 1019–1022 (2000).

    Article  Google Scholar 

Download references

Acknowledgements

We are grateful to the UK Engineering and Physical Sciences Research Council for funding this project.

Author information

Authors and Affiliations

Authors

Corresponding author

Correspondence to C. C. Phillips.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Rights and permissions

Reprints and permissions

About this article

Cite this article

Frogley, M., Dynes, J., Beck, M. et al. Gain without inversion in semiconductor nanostructures. Nature Mater 5, 175–178 (2006). https://doi.org/10.1038/nmat1586

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nmat1586

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing