Skip to main content

Thank you for visiting 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.

Stimulated emission of polarization-entangled photons


Entangled photon pairs—discrete light quanta that exhibit non-classical correlations—play a crucial role in quantum information science (for example, in demonstrations of quantum non-locality1,2,3,4,5,6,7, quantum teleportation8,9 and quantum cryptography10,11,12,31). At the macroscopic optical-field level non-classical correlations can also be important, as in the case of squeezed light13, entangled light beams14,15 and teleportation of continuous quantum variables16. Here we use stimulated parametric down-conversion to study entangled states of light that bridge the gap between discrete and macroscopic optical quantum correlations. We demonstrate experimentally the onset of laser-like action for entangled photons, through the creation and amplification of the spin-1/2 and spin-1 singlet states consisting of two and four photons, respectively. This entanglement structure holds great promise in quantum information science where there is a strong demand for entangled states of increasing complexity.

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

Relevant articles

Open Access articles citing this article.

Access options

Rent or buy this article

Get just this article for as long as you need it


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

Figure 1: The photon number (pair) distribution, P(n), arising from stimulated parametric down-conversion shifts its peak and broadens as the mean number of photons increases.
Figure 2: Experimental set-up.
Figure 3: Experimental demonstration of stimulated entanglement.
Figure 4: Two- and four-photon interference due to stimulated emission.


  1. Clauser, J. F. & Shimony, A. Bell's theorem: experimental tests and implications. Rep. Prog. Phys. 41, 1881–1927 (1978).

    Article  CAS  Google Scholar 

  2. Aspect, A., Dalibard, J. & Roger, G. Experimental test of Bell's inequalities using time-varying analyzers. Phys. Rev. Lett. 49, 1804–1807 (1982).

    Article  MathSciNet  Google Scholar 

  3. Ou, Z. Y. & Mandel, L. Violation of Bell's inequality and classical probability in a two-photon correlation experiment. Phys. Rev. Lett. 61, 50–53 (1988).

    Article  MathSciNet  CAS  Google Scholar 

  4. Shih, Y. H. & Alley, C. O. New type of Einstein-Podolski-Rosen experiment using pairs of quanta produced by optical parametric down-conversion. Phys. Rev. Lett. 61, 2921–2924 (1988).

    Article  CAS  Google Scholar 

  5. Tittel, W., Brendel, J., Zbinden, H. & Gisin, N. Violation of Bell inequalities by photons more than 10 km apart. Phys. Rev. Lett. 81, 3563–3566 (1998).

    Article  CAS  Google Scholar 

  6. Weihs, G., Jennewein, T., Simon, C., Weinfurter, H. & Zeilinger, A. Violation of Bell's inequality under strict locality conditions. Phys. Rev. Lett. 81, 5039–5043 (1998).

    Article  MathSciNet  CAS  Google Scholar 

  7. Pan, J.-W. et al. Experimental test of non-locality in three-photon Greenberger-Horne-Zeilinger entanglement. Nature 403, 515–519 (2000).

    Article  CAS  Google Scholar 

  8. Boumeester, D. et al. Experimental quantum teleportation. Nature 390, 575–579 (1997).

    Article  Google Scholar 

  9. Boschi, D. et al. Experimental realization of teleporting an unknown pure quantum state via dual classical and Einstein-Podolski-Rosen channels. Phys. Rev. Lett. 80, 1121–1125 (1998).

    Article  MathSciNet  CAS  Google Scholar 

  10. Ekert, A., Rarity, J. G., Tapster, P. R. & Palma, G. M. Practical quantum cryptography based on two-photon interferometry. Phys. Rev. Lett. 69, 1293–1295 (1992).

    Article  CAS  Google Scholar 

  11. Jennewein, T., Simons, C., Weihs, G., Weinfurter, H. & Zeilinger, A. Quantum cryptography with entangled photons. Phys. Rev. Lett. 84, 4729–4732 (2000).

    Article  CAS  Google Scholar 

  12. Tittel, W., Brendel, J., Zbinden, H. & Gisin, N. Quantum cryptography using entangled photons and energy-time Bell states. Phys. Rev. Lett. 84, 4737–4736 (2000).

    Article  CAS  Google Scholar 

  13. Slusher, R. E. et al. Observation of squeezed states generated by four-wave mixing in an optical cavity. Phys. Rev. Lett. 55, 2409–2412 (1985).

    Article  CAS  Google Scholar 

  14. Wu, L. A., Kimble, H. J., Hall, J. L. & Wu, H. Generating squeezed states by parametric down-conversion. Phys. Rev. Lett. 57, 2520–2523 (1986).

    Article  CAS  Google Scholar 

  15. Ou, Z. Y., Pereira, S. F., Kimble, H. J. & Peng, K. C. Realization of the Einstein-Podolski-Rosen paradox for continuous variables. Phys. Rev. Lett. 68, 3663–3666 (1992).

    Article  CAS  Google Scholar 

  16. Furusawa, A. et al. Unconditional quantum teleportation. Science 282, 706–709 (1998).

    Article  CAS  Google Scholar 

  17. Kwiat, P. G. et al. New high-intensity source of polarization-entangled photon pairs. Phys. Rev. Lett. 75, 4337–4341 (1995).

    Article  CAS  Google Scholar 

  18. Kok, P. & Braunstein, S. L. Postselected versus non-postselected quantum teleportation using parametric down-conversion. Phys. Rev. A 61, 042304-1–042304-10 (2000).

    Article  Google Scholar 

  19. Simon, C., Weihs, G. & Zeilinger, A. Optical quantum cloning via stimulated emission. Phys. Rev. Lett. 84, 2993–2996 (2000).

    Article  CAS  Google Scholar 

  20. Ou, Z. Y., Rhee, J.-K. & Wang, L. J. Observation of four-photon interference with a beam splitter by pulsed parametric down-conversion. Phys. Rev. Lett. 83, 959–962 (1999).

    Article  CAS  Google Scholar 

  21. Bouwmeester, D. et al. Observation of three-photon Greenberger-Horne-Zeilinger entanglement. Phys. Rev. Lett. 82, 1345–1349 (1999).

    Article  MathSciNet  CAS  Google Scholar 

  22. De Martini, F., Mussi, V. & Bovino, F. Schroedinger cat states and optimum universal quantum cloning by entangled parametric amplification. Opt. Commun. 179, 581–589 (2000).

    Article  CAS  Google Scholar 

  23. DeMartini, F. & Di Giuseppe, G. Multiparticle quantum superposition and stimulated entanglement by parity selective amplification of entangled states. Z. Naturforsch. 56, 61–66 (2001).

    CAS  Google Scholar 

  24. Weinfurter, H. & Zukowski, M. Four photon entanglement from down conversion. Preprint quant-ph/0103049 at 〈〉 (2001).

  25. Knill, E., Laflamme, R. & Milburn, G. J. A scheme for efficient quantum computation with linear optics. Nature 409, 46–52 (2001).

    Article  CAS  Google Scholar 

  26. Atature, M. et al. Partial distinguishability in femtosecond optical spontaneous parametric down-conversion. Phys. Rev. Lett. 83, 1323–1326 (1999).

    Article  CAS  Google Scholar 

  27. Herzog, T. J., Rarity, J. G., Weinfurter, H. & Zeilinger, A. Frustrated two-photon creation via interference. Phys. Rev. Lett. 72, 629–632 (1994).

    Article  CAS  Google Scholar 

  28. Milonni, P. W., Fearn, H. & Zeilinger, A. Theory of two-photon down-conversion in the presence of mirrors. Phys. Rev. A 53, 4556–4566 (1996).

    Article  CAS  Google Scholar 

  29. Cregan, R. F. et al. Single-mode photonic band gap guidance of light in air. Science 285, 1537–1539 (1999).

    Article  CAS  Google Scholar 

  30. Kim, J., Takeuchi, S. & Yamamoto, Y. Multiphoton detector using visible light photon counter. Appl. Phys. Lett. 74, 902–904 (1999).

    Article  CAS  Google Scholar 

  31. Naik, D. S., Peterson, C. G., White, A. G., Berglund, A. J. & Kwiat, P. G. Entangled state quantum cryptography: eavesdropping on the Ekert protocol. Phys. Rev. Lett. 84, 4733–4736 (2000).

    Article  CAS  Google Scholar 

Download references


We thank C. Mikkelsen, P. Varisco, W. Irvine, A. Ekert and J. Rarity for suggestions and experimental support. This work was supported by the EPSRC, the UK Defence Evaluation and Research Agency, and the European QuComm project.

Author information

Authors and Affiliations


Corresponding author

Correspondence to D. Bouwmeester.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Lamas-Linares, A., Howell, J. & Bouwmeester, D. Stimulated emission of polarization-entangled photons. Nature 412, 887–890 (2001).

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI:

This article is cited by


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


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