Inside a superconductor, electrons can bind together into so-called Cooper pairs. A new study has shown that a similar pairing between photons can occur in water and other transparent media. The researchers identified these photonic Cooper pairs through correlations in light that is scattered inelastically. The data matched a model in which the photons interact by an exchange of virtual molecular vibrations.
Normally, photons do not interact, and electrons are not attracted to each other. But in a material, effective forces can arise from interactions with the medium. In the Bardeen–Cooper–Schrieffer (BCS) model of superconductivity, electrons generate distortions in the surrounding lattice, and these distortions (or virtual phonons) can couple two electrons together. Researchers from the Federal University of Rio de Janeiro and the Federal University of Minas Gerais, Brazil, showed that a similar coupling could occur for photons.
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