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.
A. Lamas-Linares, J. C. Howell, and D. Bouwmeester, Stimulated Emission of Polarization-Entangled Photons, Nature 412(6850), 887-890.
This is a pre-copy-editing, author-produced PDF of an article accepted for publication in Nature, volume 412, issue 6850, in 2001 following peer review. The final publication may differ and is available at Springer via https://doi.org/10.1038/35091014.
A free-to-read copy of the final published article is available here.