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Nature Physics 4, 346–347 (1 May 2008) | doi:10.1038/nphys953

Cavity QED: Signs of anharmonicity

Howard Carmichael

A single photon confined to an optical cavity that is sufficiently small produces an electric field comparable to that of a standard household electrical socket. The field is strong enough to shift the energy levels of an atom trapped in the cavity by more than its emission linewidth, thus observably changing the frequencies at which light is absorbed and emitted.