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Dipole-dipole interactions between Rydberg atoms cause the optical response of a single atom to be strongly modified by its nearest neighbour. This gives rise to a cooperative non-linearity which depends not only on the light intensity but also the density of the sample. To explore this effect we use electromagnetically induced transparency to map the interacting Rydberg state onto a strong optical transition from the ground state in cold atoms [1]. The dipole-dipole interaction is observed by a suppression of the transparency on the two-photon resonance, giving a cooperative enhancement of the nonlinearity.
A new experiment is being developed to enhance the cooperative non-linear effect by confining many atoms within a single blockade sphere. This system will be used to explore single photon non-linearities and non-classical states of light [2]. [1] J. D. Pritchard et al., arXiv:0911.3523 [2] L. H. Pedersen et al., Phys Rev. A 79, 012320 (2009). |
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