Collective Lamb Shift in Single-Photon Superradiance

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Science  13 May 2010:
DOI: 10.1126/science.1187770


Superradiance is the cooperative spontaneous emission of photons from an ensemble of identical atoms that provides valuable insights into the many-body physics of photons and atoms. We show that an ensemble of resonant atoms, embedded in the center of a planar cavity, can be collectively excited by synchrotron radiation into a purely superradiant state. The collective coupling of the atoms via the radiation field leads to a substantial radiative shift of the transition energy, the collective Lamb shift. We simultaneously measured the temporal evolution of the superradiant decay and the collective Lamb shift of resonant 57Fe nuclei excited with 14.4 keV synchrotron radiation. Our experimental technique provides a simple way for spectroscopic analysis of the superradiant emission.